does anyone had any live comparison of this in the same engine??? i am sure many of us would like to know what works best.
FLATSIDE 39mm 41 mm OR EFI WIL BROS ON A 1300cc ENGINE?
Help Support VMAX Forum:
does anybody have used any of this ?? vgas or pcw flatside carbs or wild bros efi system ??? which works best ? ?
I have the vgas and had pcw flats...I can tell you brother if u are not into adjusting carbs on a regular basis stay away..the carbs are very sensitive ,,,awesome,,but very sensitive and I adjust about a few times a month,,,sometimes I have to adjust when humidity rolls around...go for the FI,,but make sure your electrical system has the r1 conversion and is running at top voltage otherwise that FI system tends to run funky..
Oh and on the 1300cc motor its borderline but id prob go with 41..
Oh and on the 1300cc motor its borderline but id prob go with 41..
electrical system r1 conversion ? ? can you give me some info aobut that. it's the first time i hear about something like that
between ufo vgas and pcw which one makes the diferrence ?
Don't waste your $$$$ or time with any of them on a 1300. Stock carbs will work best. If you like you can try the Stage 7.
IMHO
but both companys tested them on a 1260 engine and produces a lot more power than stock ,why do you say that ?
do you believe everything you read?
I believe the dyno's my friend. I have spent here in greece more than 35.000 eyros in my vmax. I have read lots of post's. I know that yamaha invented the v-boost cause in that age there werent flatside's . Cv carbs have problem with the air mixture . Not much air. Fcr doesnt. More fuel more air more hp. I am not a mechanic but at least for the v-max i think what you must do to raise the hp. And one of the things are fcr or efi. I ve seen on a dyno instant increase 18 hp without tunning in a stock engine. Do you have some proof for what you are saying. I will be glad showing to me . Maybe you will open my eyes. Maybe you know something i dont share it with me my friend. I am going to iinvest some more serious money on my vmax. And i want to be 99% sure for what is the best to raise my hp.
For example, Jim R's 1400+ cc engine dyno'd better with modified stock carbs than flat slides.
When you say modified you mean stage 7 ? Can you tell me the numbers?
KJShover
Proud Vmax lover
Stg 7 or Sean's kit. Jim's 1428 motor dynoed higher with Sean's kit than with flatslides.
I am going to be posting my dyno sheet next week, but I wanted to tell you gents my numbers.
1428cc PCW engine, stock cams/heads, Morley Muscle jet kit:
154.7 RWHP
109.9 ft/lbs of torque (the highest torque was 110.8 ft/lbs, but that run only had 153.9 RWHP.)
This is a new record for the 1428cc "stocker" that PCW builds. Another one was built alongside of mine, but had Vgas carbs..... I got him by almost 5 hp and over 4 ft/lbs of torque according to PCW. I will say that John Gainey has given all the credit for the exceptional numbers this engine produced to Sean's jet kit!!unk: John has said that he will be recommending Sean's kit to all who are buying engines of this type from him from now on. BTW this also beat out the PCW flatslide numbers as well so this isnt a bash on UFO:biglaugh:
Will post the dyno sheet soon,
Jim Rodgers
VMOA# 4046
Western Ontario Chapter Leader:rocket bike:
Well it sounds like you are set on Flat slides. But before you buy them remember you have to tune them.
For your reading pleasure..good luck:ummm:
Before you do anything, MAKE SURE THE CARBS ARE CLEAN. Tear them completely apart (don't forget to remove the idle mixture screws), blast everything with carb cleaner, and blow out all passages and jets with compressed air. If you neglect this critical step, don't be surprised when, after fourteen jet changes, you find that a shred of fuel line or bits of rust from the gas tank (yes, even on YOUR bike, even with a fuel filter) had gotten lodged in some passage or another, causing the 'jetting' problem you were trying to solve.
If you're running a ram-air setup, and the carbs don't sit inside the airbox, you'd better route the float bowl vents to the inside of the airbox or you'll never in a million years get the thing working properly.
If you're not running a fuel pump, and are relying on gravity to move the fuel from the fuel tank to the carbs, you'd better route the fuel tank vent to the inside of the airbox or you'll wonder why it keeps sputtering at the end of long straights.
And I'm not kidding about the float valve seat sizes. Scroll down to the bottom of the page to get the scoop.
Keep in mind that you will spend much less time tuning the carburetion in following order:
1. Main fuel jet and main air jet (must be selected first since they feed the emulsion tube, which feeds the needle jet and jet needle).
2. Needle: a. root diameter b. taper c. clip position (which includes the L1 measurement)
3. Slow fuel and air jets.
4. Fuel screw
5. Accelerator pump (It helps to leave this disconnected during dyno testing so as not to create a momentary artificially rich condition which may lead to misleading exhaust gas analyzer readings. However, it's surprisingly time consuming to remove or install the pump connecting rod. If I had all the time in the world and were doing development work, I'd disconnect it. If I were at all in a rush, I'd leave it connected and just hold the test point a little longer to let the EGA get a solid reading.)
You may find that if you change the taper of the needle a great amount, you may have to go back and reselect the main fuel and air jets since the tip of the needle can affect the full throttle mixture.
Synchronizing:
I've had pretty good luck synchronizing the carbs off the bike. Using the shank of a very small drill bit, adjust the idle speed screw until you can barely fit the base of the drill bit under one of the slides as you would a feeler gauge. You may have to remove the idle speed screw from the carbs and temporarily remove its locking spring to be able to thread the screw in far enough to slide a drill bit in unless you have some pretty small bits. Do this from the engine side of the slide as opposed to the intake side, and make sure the carbs are oriented such that the slides are moving vertically, so their weight takes up any slack in the throttle linkage. Remove the top of the carbs as you would to access the needles. On the throttle shaft in each carb there is an arm which controls slide movement. It is secured by a screw and nut. The nut is used for adjustments, the screw is to lock the adjusting nut in position. Loosen the lock screw of the slide you are trying to adjust, turn the adjusting nut to set the slide so the drill bit just scrapes under, and tighten the lock screw. Repeat for each slide. Be prepared to spend about five times as long as you think it should take, going back and forth between slides to get everything just right. Replace idle speed screw locking spring. Because the carbs must be disassembled to access the adjusting mechanisms, I recommend using the above procedure. You could use manometers to synchronize the carbs as you would a set of CVs, but you'd have to start and warm the bike, check vacuum levels, shut the bike off, disassemble the carbs, adjust, reassemble, restart the bike, and recheck vacuum levels. You may very well kill the battery (or your bump start helpers) before you finished synching the carbs this way. It has been my, and others', experience that the lock screws tend to work loose with time no matter how surely you tighten them. To remedy this, after the slides are synchronized, clean the adjusters with brake or contact cleaner, blow them dry, and put a drop of silicone over their tops. You can also use Loctite 290, but it tends to make future adjustments a bit difficult. Once the bike is up and running, if manometers show that the synchronization is off by a considerable amount at idle speed, but even out as the throttle is opened, it's entirely possible that the cylinders want different idle mixtures. This is not at all uncommon, especially on V-twin engines where the intake tracts are dissimilar such as Ducati 2 valve 750s and 900s. But you'd better go and check your valve clearances first to make sure a valve isn't hanging open. If the vacuum levels are off and you're working on a V engine of some sort, make sure you didn't botch up the cam timing on one bank.
Fuel screw:
With the carbs synched, the engine warmed up to operating temperature, and the idle speed set, adjust the fuel screws so that when you rev the bike in neutral and release the throttle, the revs quickly drop to exactly idle speed again. If, when you release the throttle, the revs hang up a few hundred rpm above idle speed, then drop to idle, the idle mixture is probably a bit too lean. Turn the fuel screws out. Use a minimum of half turn increments until you know you've just about nailed it. You'll drive yourself up the wall trying to tune the thing in eighth or quarter turn increments if you're a mile off. In extremely lean cases the idle will hunt between the proper speed and something above it. If, when you release the throttle, the revs drop below idle speed then pick up, the idle mixture is probably a little bit too rich. Turn the fuel screws in. In extremely rich cases the engine will die after revving the bike and releasing the throttle, unless you've turned the idle speed screw way in, in which case it may act like the idle mixture is a little bit too lean. In slightly rich cases, the engine will respond well to throttle blips when cold, but will die or dip slightly below idle speed when hot. While having an exhaust gas analyzer is almost mandatory during tuning of main and needle circuits, do not rely totally on them to set idle mixture. Use an accurate tachometer (like your ear) and adjust the fuel screws to find the highest vacuum for each cylinder or highest idle speed, which will often be the same setting.
Slow fuel jet:
After setting the fuel screws, if you end up having to turn them in closer than 1 turn out from bottomed, select smaller slow jets. If you end up with the fuel screws turned out further than 2 turns from bottomed, select larger slow jets. Go back and repeat the fuel screw adjustment procedure. You have the correct slow jets when your engine passes the fuel screw adjustment procedure (settles to a steady idle after throttle blip) with a fuel screw setting between one and two turns out from lightly bottomed. A good way to see if the slow fuel jet is too large is to slowly turn the fuel screw closed and see if the bike still idles. If you get the fuel screw down to something like half a turn out, or closed, and that cylinder is still firing, the slow fuel jet is probably too big.
Slow air jet:
With the correct slow fuel jets installed and the fuel screws adjusted as above, when you are operating the engine at higher revs and closed to 1/10th throttle (say, while transitioning from trailing to neutral throttle or running with no load at some mid rpm), if the mixture is too rich, use a larger slow air jet. If the mixture is too lean, use a smaller slow air jet. It is rather easy to confuse this circuit with the needle’s root diameter since they overlap quite a bit. If the needle’s root diameter is very far from perfect, you will be trying to make up for problems created by that instead of dialing in the slow speed circuit. Conversely, if the slow air jet is a mile out, you’ll have a hard job of selecting a needle root diameter. To help resolve problems with this, be conscious of the fact that the slow air jet will tend to have a more pronounced effect at lesser throttle openings, and the needle's root diameter, very slightly greater.
I should point out here how the air jets and fuel jets interact. I can do this most easily with a little graph.
This graph is 100% a figment of my fevered imagination, and is only to be used as a general guide, not an absolute definitive end all be all word of truth. That said..
1. air jet way too small
2. air jet a little bit too small
3. air jet just right
4. air jet a little bit too big
5. air jet way too big
So basically what happens is if you have the mixture right at low rpm, and it's too rich at high rpm, the air jet is too small and you need a bigger one. Or if you have it just right at high rpm and it's too lean at low rpm, you have an air jet that's too small and you need a bigger one. Or if you have the mixture just right at low rpm and it's too lean at high rpm, the air jet is too big and you need a smaller one. Do I really need to type the fourth combination? When you put in a bigger air jet, it leans things out everywhere, but more at higher engine speeds. And when you put in a smaller air jet, it richens things up everywhere, but more at higher engine speeds. Then when you get the right air jet, it might be too rich or too lean everywhere, so now you have to go and put in a smaller or bigger fuel jet to fix things up again. So you control the shape of the graph with the air jet, and move it up and down with the fuel jet. The same thing is supposed to apply when working with the main air jet and main fuel jet, but it doesn't on FCRs, for reasons which I'll get into further down. But it's supposed to, damn it.
Slow air screw:
Some FCRs are equipped with a slow speed air screw in place of the slow air jet. They rock. Buy some, from Sudco, because they rock. You need the screw plus a little locking spring. The part numbers are 012-230 for the screw, and 021-235 for the spring. It'll probably cost about $60 after shipping to get four of each (um, I'm assuming you're tuning a four cylinder there). Yeah, I know that's a lot of money for four jets. But look at it like this, the jet and spring together cost something like $12. One slow air jet costs something like $4.50. If you think for one second that you're going to get the right jet size on the first try, you've obviously never done this before. If you think you're going to get it on the second try, you're Merlyn Plumlee (Is Merlyn not the coolest name for a mechanic or what?). So just buy the adjustable jet and be done with it. Aside from not having to buy a bunch of different jets, it also allows much faster changes in calibration as you need only to turn a screw as opposed to changing a jet, and you can do it with the engine running in many installations, so you can _listen_ for the change in mixture. Some air filter adapters have a 4mm passage leading to the slow air jet, some a 6mm passage. If your carbs have slow air screws and the 4mm adapters, drill the adapters' slow air passage to 6mm. This will allow you to access the air screw with a screwdriver big enough to actually turn it, but will leave a hole small enough that the jet can't fall out and get sucked into the engine if it for some oddball reason works loose (that's probably never happened in the history of the world, but it makes me feel better knowing it can't). The following number of turns out are shown with the slow air jet size they are approximately equal to. Note that the change in jet number is not linear with the number of turns out. The screw adjusters are much more sensitive at lesser openings since the screw is still moving linearly at a constant distance per turn, but the flow area is changing more or less as a function of distance open, so half a turn out is two times as rich as one turn out, but one and a half turns out is only fifty percent leaner than one turn out. Or something like that. And don't e-mail me to say look dude half a turn out is a 65 and one is a 100 and one and a half is a 125, go and find the area of the aperture of each one of those jets first then hit yourself over the head with the calculator. Like this even matters...
Number of turns out
on air screw
Approximately equal
to this slow air jet
1/4
45
3/8
55
1/2
65
5/8
75
3/4
85
7/8
95
1
100
1 1/8
110
1 1/4
120
1 1/2
125
1 3/4
130
2
135
2 1/4
140
2 1/2
145
2 3/4
150
3
155
Main fuel jet:
The proper main fuel jet will give best full throttle performance, but also affects mixture as far down as 1/8 throttle. I know you don't believe this second part, because I didn't believe it until I saw it happen while tuning an extensively instrumented test engine. Suspend your beliefs about the main fuel jet only affecting mixture when the slide is all the way up & the needle is all the way out of the needle jet and think for a minute. The main fuel and air jets feed the emulsion tube which feeds the needle jet and jet needle. When a more fuel rich emulsion is bled past the same restriction (needle jet area minus jet needle area), the engine gets more fuel. You must select the full throttle jetting first. If you go and find a needle that works with the wrong main jets, it won't work with the right ones, and you'll have to go through the needle selection process all over again when the main jets are correct. Trust me.
Main air jet:
If you find that the engine runs perfectly at WOT near the torque peak, but becomes lean toward redline, select smaller main air jets. Conversely, if the engine runs perfectly near the torque peak but richens toward redline, select larger main air jets. Changes in air jets may require changing the main fuel jet. Say you have good performance at engine speeds leading to the torque peak under wide open throttle with a 150 main fuel jet and 200 main air jet. Should you need to richen the mixture at full revs and full throttle and select a 180 main air jet, you may need to go down to a 145 or 140 main fuel jet to keep the lower rpm mixture the same as with the 150/200 combination. Generally (there are always exceptions), once the main air jets are properly selected for the intended application, they need not be changed again unless you change the intake restriction (modify the airbox or use different filter) or change engine or exhaust specification. Varying atmospheric conditions can usually be dealt with by fuel jet, fuel screw, and needle changes.
The part that really sucks about FCR carburetors is that they come with primary type emulsion tubes as opposed to the bleed type emulsion tubes every other four stroke carb in the whole universe ever used. What this means, essentially, is that the above paragraph doesn't actually have any connection to reality. It has been my experience that if you for whatever reason have something like a 200 main air jet in the carbs, and the mixture goes lean at high rpm, and you manage to get the mixture sorted out by putting in different (smaller) main air jets and main fuel jets, then the carbon monoxide numbers might be really pretty and even from mid rpm through redline, BUT THE ENGINE ISN'T MAKING AS MUCH POWER AS IT DID WITH THE BIG MAIN AIR JETS. I think this has something to do with a bigger air jet allowing the fuel coming up through the needle jet to get emulsified more before going up into the venturi, therefore allowing better atomization, and more complete burning of the fuel supplied into the cylinder, since lots of little bitty fuel droplets have more surface area per unit of volume and burn more completely, as opposed to a few big fuel droplets having less surface area per unit volume and not only burning less completely, but because they burn less completely you need to have more of them to burn the oxygen available, which means the CO and hydrocarbon numbers go up because lots of unburned fuel is hanging around throughout the combustion process, soaking up heat and getting pumped out the exhaust port. Or something.
When using a carbon monoxide meter to track exhaust gas readings, do not fall into the trap of aiming for the same CO reading at every rpm. It is quite rare for an engine to make best power at every rpm with the same CO reading. You must determine what the engine wants at each rpm, then tailor the fuel curve accordingly.
Okay, here's a good place to put the CO and O2 graph, so you know why CO is a good indicator of rich or lean conditions in gasoline burning engines being tuned for maximum power.
So the little red box is where you're aiming. It has been my experience that best power is usually had with a CO reading somewhere between 2% and 6%. That'll give you an air fuel ratio somewhere in the neighborhood of 12:1 to maybe 13.5:1. These numbers are not absolutes, don't call the SAE on me here. I don't even really know for sure that the CO and O2 graphs cross at 14.7:1, but I put it there because what the hell good is an air fuel ratio graph without having 14.7:1 on there somewhere? I think it's a tradition or something. But the deal is, if you look at the graphs, the CO graph is relatively steep compared to the O2 graph in this range of air fuel ratios, so for a small change in air fuel ratio, there's a relatively large change in CO reading, which is good, because then you have a clue what just happened when you changed jets. If you try to use O2 as an indicator in this range, what you end up with is a small change in O2 value for a large change in air fuel ratio, so you need super duper accurate equipment which is hideously expensive, so bike tuners don't have it, so you can't use it anyway, never mind that it's dumb in the first place. You won't need a CO reading to tell you when it's above about 10% or below about 1%, because you'll be able to hear the engine misfiring. But it's still nice to know which way you need to go, because it's not always immediately obvious. And one thing about using CO as an indicator is that if you get anywhere on the low side of about 1%, you're super duper lean. 0.5% is way way leaner than 1%, and 0.2% is way way way way way leaner than 0.5%. And if you look at the graph of CO above, you'll see why that's true. So what I'm saying is if you see 0.5%, don't even bother making some little change like one jet size or half a turn on a mixture screw or air jet. You need to make a big change in the rich direction.
Needle code:
1st letter indicates taper. Letters toward the beginning of the alphabet are leaner (more gradual taper), letters toward the end of the alphabet are richer (more drastic taper).
2nd letter indicates the L1 measurement. This is the distance from the top adjustment clip to a portion of the needle where the diameter is 2.515 millimeters. Letters toward the beginning of the alphabet are richer (shorter measurement), letters toward the end of the alphabet are leaner (longer measurement).
3rd letter indicates starting dimension or root diameter of needle. Letters toward the beginning of the alphabet are richer (thinner diameter), letters toward the end of the alphabet are leaner (thicker diameter).
Needle codes for 28-33mm (90xxx) and
35-41mm (OCxxx) FCRs are listed below.
Code
Taper
L1mm for
28-33mm
L1mm for
35-41mm
Diameter mm
A
L1mm for
28-33mm
L1mm for
35-41mm
Diameter mm
A
56.25
72.20
2.605
B
72.20
2.605
B
56.70
72.65
2.615
C
72.65
2.615
C
57.15
73.10
2.625
D
0d 45"
57.60
73.55
2.635
E
1d 00"
58.05
74.00
2.645
F
1d 15"
58.50
74.45
2.655
G
1d 30"
58.95
74.90
2.665
H
1d 45"
59.40
75.35
2.675
J
2d 00"
59.85
75.80
2.685
K
2d 15"
60.30
76.25
2.695
L
2d 30"
60.76
76.70
2.705
M
2d 45"
61.20
77.15
2.715
N
3d 00"
61.65
77.60
2.725
P
73.10
2.625
D
0d 45"
57.60
73.55
2.635
E
1d 00"
58.05
74.00
2.645
F
1d 15"
58.50
74.45
2.655
G
1d 30"
58.95
74.90
2.665
H
1d 45"
59.40
75.35
2.675
J
2d 00"
59.85
75.80
2.685
K
2d 15"
60.30
76.25
2.695
L
2d 30"
60.76
76.70
2.705
M
2d 45"
61.20
77.15
2.715
N
3d 00"
61.65
77.60
2.725
P
62.10
78.05
2.735
Q
78.05
2.735
Q
62.55
78.50
2.745
R
78.50
2.745
R
63.00
78.95
2.755
S
78.95
2.755
S
63.45
79.40
2.765
T
79.40
2.765
T
63.90
79.85
2.775
U
79.85
2.775
U
64.35
80.30
2.785
V
80.30
2.785
V
64.80
80.75
2.795
W
80.75
2.795
W
65.25
81.20
2.805
X
81.20
2.805
X
65.70
81.65
2.815
Y
81.65
2.815
Y
66.15
82.10
2.825
Z
82.10
2.825
Z
66.60
82.55
2.835
82.55
2.835
Example 1: A 90FTV needle would have a taper of 1degree 15", an L1 dimension of 63.90mm, a root diameter of 2.795mm, and be intended for use in the small FCRs.
Example 2: An OCEMR needle would have a taper of 1 degree 00", an L1 dimension of 77.15mm, a root diameter of 2.755mm, and be intended for use in the large FCRs.
Needle selection:
1st letter: This portion of the needle controls mixture between approximately 1/3 and full throttle. If the engine fails to respond to main jet changes, you may be too lean on this, causing the tip of the needle to be very large. This would tend to artificially limit fuel flow at full throttle, taking control of WOT fuel delivery away from the main jet. Selecting this is much easier than many believe. If you find that mixture is good at 1/4 throttle, but too rich at 3/4, you probably have a needle with too great a taper angle. If the mixture is good at 1/4 throttle, but too lean at 3/4, you probably have a needle with too small a taper angle. I know you went and made sure the main jets were sorted out before testing the needle taper, right?
2nd letter: This generally doesn't need to be played with much. If, when adjusting the clip, you find that you are at the 1st groove and still need to start the taper later, you may need to select a needle with a longer L1 dimension. If you find yourself at the 7th groove and needing to start the taper earlier, you may need to select a needle with a shorter L1 dimension.
3rd letter: This portion of the needle has the greatest effect on mixture between closed and 1/4 throttle. If the engine is too rich while gradually accelerating through 1/8 throttle, select a needle with a larger root diameter. If the engine is too lean when gradually accelerating through 1/8 throttle, select a needle with a smaller root diameter. You will drive yourself completely batty trying to sort out this if the slow fuel and air jets aren't right. Conversely, you will drive yourself completely batty if you try to sort out the slow fuel and air jets if the needle root diameter isn't right. So you're pretty much screwed either way here. And if you didn't set the float level to 9mm, just go jump off a cliff right now and get it over with because that will have a fairly large effect on how much fuel spurts up through the needle jet when the slide's only open a little bit.
Clip position: This controls mixture between approximately 1/8 to 7/8 throttle. Higher clip position for leaner, lower for richer. Unlike taper, this setting will change mixture (approximately) evenly throughout the throttle position range, with a slight tendency to affect the lesser throttle positions more than greater. You should work to find a needle which allows you to run the clip on the 3rd, 4th (middle), or 5th position. If you find that mixture at 1/3 through 3/4 throttle is too lean, raise the needle!
Float level: Higher float levels richen mixture at full throttle low rpm, and part throttle high rpm, lower leans it, but do not change it more than two millimeters in either direction of 9mm. I have caused myself more headaches playing with float level on FCRs than any other adjustment of the carburetor. If you can possibly run the floats at 9mm, do so. To set float level, with the carbs off the bike and the float bowls removed, hold the carbs in such a manner that the float pivots are above the floats. Tilt the carbs until the float you are adjusting just kisses its float valve needle, but doesn't compress the float needle's internal spring. Measure from the float bowl sealing surface to the highest (lowest with the carbs mounted to the bike) point of the float at a 90 degree angle to the sealing surface. Bend the float tab that touches the little nub on the needle to change the float height.
Float valve size: These should be sized according to horsepower which will be fed by each carb, and whether the fuel bowls will be supplied via gravity feed or a fuel pump (I suggest using a max pressure of 3.0 psi, since when I tried using 3.5 psi, I kept pumping the cylinders full of gasoline with the engine off...). Do not use 2.8mm or 3.2mm valves with pressure feed, as the increased area of the float valve will allow fuel pressure to overpower the float needle's little internal spring, pushing it down, letting fuel in, and flooding the fuel bowl.
Float valve size
in millimeters
HP per carb
gravity feed
HP per carb
3psi feed
2.0
20-28
29-37
2.4
24-34
37-50
2.8
33-41
Not recommended
3.2
39-50
Not recommended
[FONT="]Don't bother with the test where you shift through the gears. That test was[/FONT][FONT="]really designed as a way to quantify changes in slide damping in CV carbs. It[/FONT][FONT="]will show you how the engine picks up after a shift, so you may be able to find[/FONT][FONT="]a problem if the accelerator pump isn't adjusted correctly or if the needles[/FONT][FONT="]are really a mile off, but the accelerator pump is the last thing you're going[/FONT][FONT="]to play with since the jetting has to be finalized before you can get any[/FONT][FONT="]meaningful feedback with accelerator pump changes, and there are better ways to[/FONT][FONT="]test the needle taper and position. So you'll be doing roll-on tests. Don't[/FONT][FONT="]bother fiddling around with 4th gear; put the bike in top gear for testing. You[/FONT][FONT="]want to load the engine as much as possible, and have it spin through the rev[/FONT][FONT="]range as slowly as possible, to have any hope at all of getting an idea why[/FONT][FONT="]it's running badly. If you run the bike in a low gear and it just goes[/FONT][FONT="]"WOOOOIIIIP" through the revs, then you won't have enough time to listen to the[/FONT][FONT="]engine at various speeds. If it does something funky, you'll have nothing to go[/FONT][FONT="]on but one squiggly power output line on the graph. One of the neat things[/FONT][FONT="]about a brake dyno is you can just run the bike at one speed and listen to it[/FONT][FONT="]as long as you like. So try to make the inertial dyno as much like a brake dyno[/FONT][FONT="]as possible by running with as little mechanical advantage as possible, which[/FONT][FONT="]is top gear. On your 400, it won't be spinning fast enough at the top of sixth[/FONT][FONT="]to hurt anything (guys spin their R1s and XXs up to the top of top gear on the[/FONT][FONT="]all gear test, so…). If the dyno has a brake to slow the drum down after a run,[/FONT][FONT="]that'd be nice so you don't have to let the 400 bring it back down with engine[/FONT][FONT="]braking and its little bitty rear brake, but if that's what it takes, then… you[/FONT][FONT="]might be buying some brake pads.
[/FONT][FONT="]I forget if you're running 32mm or 33mm FCRs on that thing, and I haven't any[/FONT][FONT="]idea if it's a 400 with kit cams or a 560 with stock 400 cams, or what, but[/FONT][FONT="]even a crazy 400 with big carbs and cams and stuff (within reason) should be[/FONT][FONT="]able to take full throttle before 9k rpm, unless you've got an exhaust system[/FONT][FONT="]from hell that's creating a really nasty reversion problem in the midrange. The[/FONT][FONT="]engine might be a slug under 9k, but it should at least run without bucking and[/FONT][FONT="]misfiring at full throttle and, say 6k rpm or so. [/FONT][FONT="]If the mixture is a little bit rich or lean, the engine will be down on power[/FONT][FONT="]compared to perfect jetting. That's pretty obvious. What might not be obvious[/FONT][FONT="]is that if it's a little more rich or lean, it'll misfire a bit, which you'll[/FONT][FONT="]be able to hear as a bit of roughness, and feel as hiccups in power delivery[/FONT][FONT="](with some experience, you might be able to put your hand on the bike's frame[/FONT][FONT="]during the run and actually _feel_ the misfires). If it's _really_ rich or[/FONT][FONT="]lean, it'll be obviously popping, sputtering, and maybe even bucking around a[/FONT][FONT="]bit.[/FONT][FONT="]So if the bike is misfiring at WOT in the mid revs, but runs pretty cleanly up[/FONT][FONT="]top, then the main air jet is probably wrong, which means the air:fuel ratio[/FONT][FONT="]isn't remaining sort of constant through the rev range. For example, if it's[/FONT][FONT="]too small, the high rev range and full throttle might be okay with little main[/FONT][FONT="]fuel jets, but in the midrange at full throttle it's too lean, which would[/FONT][FONT="]delay when you could open the throttle, so you'd have to go bigger on the main[/FONT][FONT="]fuel jets to richen things up across the board then go bigger on the main air[/FONT][FONT="]jets to lean things out as the revs rise. That's all in my little tuning guide,[/FONT][FONT="]but I wanted to reiterate it since it strikes me that this may be the case with[/FONT][FONT="]your bike.[/FONT][FONT="]One thing that's not in the tuning manual is, unfortunately, the FCR main air[/FONT][FONT="]correction circuit really sucks. It doesn't respond at all well to changes in[/FONT][FONT="]the air jet. While some carbs will noticeably change the fuel curve with only a[/FONT][FONT="]5% or 10% change in the main air jet, FCRs need a big kick in the ass before[/FONT][FONT="]the WOT fuel _curve_ (think of WOT air:fuel ratio plotted against rpm) changes[/FONT][FONT="]instead of sort of changing things across the board like the main fuel jet[/FONT][FONT="]does. So you might have to go from a 100 main air jet all the way up to a 200[/FONT][FONT="]to get the effect you want, and if you're already at a 200, you might have to[/FONT][FONT="]pull the main air jet right out and run the air correction circuit with no[/FONT][FONT="]restrictor. And one thing I've noticed with the big body FCRs is that _most_[/FONT][FONT="]bikes run better with bigger air jets regardless of whether the fuel curve is[/FONT][FONT="]right or not. I think it might have something to do with atomizing the fuel so[/FONT][FONT="]it doesn't emerge from the needle jet into the venturi in a bunch of big[/FONT][FONT="]incombustible blobs, but I'm not really sure. Anyway, I'm getting off-track.[/FONT][FONT="]So let's go through setting the bike up on the dyno. Adjust the front wheel[/FONT][FONT="]chock such that the rear axle is a bit forward of the dyno roller's axle, but[/FONT][FONT="]not so much that when the bike's making power and the forks are compressed the[/FONT][FONT="]tire hits the deck of the dyno. What you're trying to do is get the bike to[/FONT][FONT="]'wedge' itself into the dyno roller under power. If a bike is too far back, it[/FONT][FONT="]may spin the tire and start to hop on the roller, though a 400 in top gear[/FONT][FONT="]probably doesn't spin the tire hard enough to do that. Run whatever the max[/FONT][FONT="]rated pressure for the tire casing is to reduce carcass flexing and heat[/FONT][FONT="]buildup. I _seriously_ doubt an FZR400 on an inertial dyno will put enough[/FONT][FONT="]stress into a tire to do any heat damage, but there's no sense in not taking[/FONT][FONT="]such an easy precaution as setting the tire pressure. Strap the bike down and[/FONT][FONT="]cinch it down just enough that the tire doesn't creep too much on the roller.[/FONT][FONT="]Cinching it down just a bit more than the rider's weight should be plenty. Make[/FONT][FONT="]sure the rear wheel is perpendicular to the roller, because if it's not, the[/FONT][FONT="]bike will push to one side when you start putting some power down. I hope you[/FONT][FONT="]have a starter in the engine or the dyno has a starter, because bump starting a[/FONT][FONT="]bike every time you have to make a dyno run is a pain in the ass. Take the fuel[/FONT][FONT="]pump off the tank, hook it up to fuel supply bottle that you can hang from[/FONT][FONT="]something in the room, and run the bike without the tank cover or gas tank in[/FONT][FONT="]place. FZR400 gas tanks, as you're probably well aware, are a royal pain in the[/FONT][FONT="]ass to take out and put in and take out and put in when you're trying to pull[/FONT][FONT="]the carbs apart after every test. So anything you can do to speed up the[/FONT][FONT="]process is good. Don't worry too much about how the tank cover might change[/FONT][FONT="]airflow to the carbs or anything like that. The effect is so minimal that it's[/FONT][FONT="]not worth the effort of running the bike like that when you're hacking away at[/FONT][FONT="]big problems like you've got. If you're running a carbon fibre can and you can[/FONT][FONT="]put fans on the radiator _and_ the exhaust system near the muffler, that'd be[/FONT][FONT="]nice so you don't burn it up. Anyway, so the bike's on the dyno and running.[/FONT][FONT="]Get it spinning up into top gear, then adjust the idle stop in until the bike[/FONT][FONT="]is 'idling' at some speed above which it wants to jump around like it's going[/FONT][FONT="]to jerk itself out of the wheel chock and kill someone. With FCRs, you might[/FONT][FONT="]have to take that little idle screw lock spring and washer off to screw it in[/FONT][FONT="]that far. I'm not really sure about that one though. Let it warm up mostly to[/FONT][FONT="]operating temp before trying to get any meaningful data. When you're really a[/FONT][FONT="]mile off on the jetting, keeping the operating temperature a constant isn't too[/FONT][FONT="]important, but when you start getting close to nailing it, you've got to keep[/FONT][FONT="]the engine at the same temp for each test or you might fool yourself into[/FONT][FONT="]thinking the extra 0.3hp you got was due to something besides the fact that the[/FONT][FONT="]thing was running 160 deg F for the first test and 190 for the second, and it[/FONT][FONT="]just happens to turn out that the bike makes more power at 190. Or whatever.[/FONT][FONT="]Marc has this really nifty Raytek infrared thermometer to check the temp of the[/FONT][FONT="]top of the radiator and maybe the oil filter, just to keep things comparable[/FONT][FONT="]between tests, but the stock temp gauge should suffice. Just try to keep the[/FONT][FONT="]bike running up around the temp you see when racing, while you're testing. If[/FONT][FONT="]that means you have to throw a few runs away until the bike heats up, or let[/FONT][FONT="]the bike idle for five minutes with the dyno fans going, so be it. Anyway, keep[/FONT][FONT="]an eye on the temp gauge. [/FONT][FONT="]DISCONNECT THE ACCELERATOR PUMP ROD from the throttle linkage during dyno testing. You don't want the extra fuel injected while you're opening the[/FONT][FONT="]throttle to mask a lean condition or make it seem rich when it's not, and[/FONT][FONT="]confuse you. It's a big hassle to pull that rod off then reinstall it, I know.[/FONT][FONT="]But do it.[/FONT][FONT="]When you start the test, open the throttle as soon as the revs allow. If it[/FONT][FONT="]will accept full throttle by 5k rpm without acting like you just flipped the[/FONT][FONT="]kill switch or bucking around like crazy, have the throttle open by then, even[/FONT][FONT="]if it sputters a bit. Don't bother running all the way to the rev limiter[/FONT][FONT="]during the 'getting it close' stages of testing unless you've got a big problem[/FONT][FONT="]right near the shift point that has to be sorted out, since it's not strictly[/FONT][FONT="]necessary to get data for the last 1k rpm or so while you're just hacking away[/FONT][FONT="]at a problem in the midrange.[/FONT][FONT="]Trying to tune an engine with a Dynojet is, as you've found, incredibly[/FONT][FONT="]frustrating. That equipment really doesn't provide enough information from[/FONT][FONT="]which to make an informed decision when changing jetting. I have a lot of[/FONT][FONT="]respect for the guys who can get a bike running well on one of those things,[/FONT][FONT="]because doing so requires ingenuity, a near mystical ability to listen to and[/FONT][FONT="]feel a bike run and tell if it's still not perfect, and persistence, because[/FONT][FONT="]they've got to really work for the information and then pull the bike apart a[/FONT][FONT="]whole bunch of times to make changes that bracket the settings they're trying[/FONT][FONT="]to find. What you've got to do (here's the ingenuity part) is find a way to[/FONT][FONT="]artificially richen and lean the mixture on the fly, so you can run a test, let[/FONT][FONT="]the roller spin back down, quickly change the mixture, then immediately make[/FONT][FONT="]another run to see if the bike runs better or worse. You're not really[/FONT][FONT="]fine-tuning so much as just finding a direction to go with the next jet change.[/FONT][FONT="]A nifty way to do this is gather up all the float bowl vent tubes into a small[/FONT][FONT="]manifold in which you control the ambient pressure. In English, that means[/FONT][FONT="]buying three T or Y vacuum hose fittings and a few feet of vacuum line, running[/FONT][FONT="]carb float vents 1 and 2, and 3 and 4 together, then left and right together,[/FONT][FONT="]and then either getting fancy and using some sort of hand pump with a[/FONT][FONT="]pressure/vacuum gauge like maybe a Mighty-vac if you've got one, or maybe[/FONT][FONT="]running one more T fitting in the line and hooking up some sort of pressure[/FONT][FONT="]gauge like an automotive fuel pressure gauge and using some sort of syringe or[/FONT][FONT="]pressure bulb or something to control the pressure in the float bowls. You're[/FONT][FONT="]not going to be pumping 2psi of air in there (the stock fuel pump only puts out[/FONT][FONT="]something like 3.5 psi); it'll be more like a quarter psi or something like[/FONT][FONT="]that, just a few inches of mercury, however that works out. You could just blow[/FONT][FONT="]or suck on the hose to get the proper effect, but I never told you that. So[/FONT][FONT="]when you increase the pressure in the float bowls, more fuel will squirt[/FONT][FONT="]through the jets, so the mixture will richen, just like with ram-air bikes.[/FONT][FONT="]Well, they pressurize the float bowls to keep the mixture constant when the[/FONT][FONT="]pressure in the airbox increases, but you get the idea. Then if the bike runs[/FONT][FONT="]better, you know you've got to pull the carbs apart and put bigger jets in it.[/FONT][FONT="]If you manage to hold a steady pressure for the whole test, and power gets[/FONT][FONT="]better in the middle but worse on top, then you know you've got to find a way[/FONT][FONT="]to richen the middle without richening the top, so you'd put in bigger main[/FONT][FONT="]fuel jets _and_ bigger main air jets during the change. If it got better[/FONT][FONT="]everywhere, then you'd just put in bigger main fuel jets.[/FONT][FONT="]The other way to richen things up is to just tape over the mouths of the[/FONT][FONT="]velocity stacks or tape up a bunch of the air filters (I'm assuming you're[/FONT][FONT="]running open stacks or indvidual filters, not an airbox, but if you are, then[/FONT][FONT="]you'd just tape up the airbox entry). With the tape deal, you've got to make[/FONT][FONT="]big changes. If you want to make things richer, don't tape up 10% of the area[/FONT][FONT="]and expect to be able to tell the difference on the next run; tape up half or[/FONT][FONT="]two thirds of the area then run another test. Unfortunately, the tape-things-up[/FONT][FONT="]method doesn't allow you to lean the mixture, it's not linear through the rev[/FONT][FONT="]range (more effect at higher revs), and it's pretty useless for part throttle[/FONT][FONT="]tests, so you have to sort of extrapolate that if the bike runs poorly and you[/FONT][FONT="]tape things up and it runs even worse that it's probably already too rich and[/FONT][FONT="]needs to be leaned out, but you'd have to use a whole lot of tape for a 1/4[/FONT][FONT="]throttle test to choke off the air supply enough to make a difference. But you[/FONT][FONT="]can be pretty damned sure that if it runs badly at full throttle, you tape up a[/FONT][FONT="]bunch of the air intake area, and it makes _more_ power, then it's _got_ to be[/FONT][FONT="]lean.[/FONT][FONT="]Once you've got the full throttle jetting nailed, it's time to figure out stuff[/FONT][FONT="]with the needles. Use a felt tip marker like a Sharpie to mark closed, 1/4,[/FONT][FONT="]1/2, 3/4, and full throttle on the throttle grip right by the housing. The way[/FONT][FONT="]I do it is to twist the grip enough to take up the slack in the pull cable,[/FONT][FONT="]then put a mark on the grip right next to the parting line for the upper and[/FONT][FONT="]lower halves of the throttle housing, then go to full throttle and mark that,[/FONT][FONT="]then just eyeball 1/2 throttle, then 1/4 and 3/4. So now just go back and make[/FONT][FONT="]pulls at 3/4, 1/2, and 1/4, doing the same thing as you did with the full[/FONT][FONT="]throttle testing until the bike pulls smoothly and cleanly at each throttle[/FONT][FONT="]position through the whole rev range. Yes, do pulls at 1/4 throttle, even[/FONT][FONT="]though it takes forever and a day to spin up. If you get the thing running well[/FONT][FONT="]at 3/4 throttle, but have to use a different needle clip position to get it to[/FONT][FONT="]run well at 1/4 throttle, then you know you need a needle with a different[/FONT][FONT="]taper. Of course, it helps to have a whole bunch of needles handy.[/FONT][FONT="]Once you've got the needles sorted out, it's time to play around with the slow[/FONT][FONT="]fuel and air jets. If you're buying jetting parts, call up Sudco and get the[/FONT][FONT="]screw in slow air jets. They're worth their weight in gold (which is a good[/FONT][FONT="]thing, because I think that's how Sudco figures their price) in the time they[/FONT][FONT="]save trying to get that circuit sorted out. Run the thing up to whatever rpm[/FONT][FONT="]you think you're going to use while just cracking the throttle open mid-turn,[/FONT][FONT="]and work around there. Spin it up over that rpm, then let the roller spin down[/FONT][FONT="]to speed, then crack the throttle open and slowly roll through the closed to[/FONT][FONT="]just barely cracked open area, listening and feeling for the bike to pop or die[/FONT][FONT="]or sputter or whatever. Do what you have to to get that part right, which is a[/FONT][FONT="]REAL bitch, because the needle root diameter, start of taper, slow air jet,[/FONT][FONT="]slow fuel jet, and fuel mixture screw all mix it up there, and it's super easy[/FONT][FONT="]to really botch things up with everything being a band-aid for the next. If[/FONT][FONT="]you're running open stacks, you might try peeking in there while the bike is[/FONT][FONT="]running and seeing where the straight part of the needle starts changing to the[/FONT][FONT="]taper as you pull the slides up and the needle comes up through the needle jet,[/FONT][FONT="]to get an idea where the problem might be. If you have a problem at, say, 4k[/FONT][FONT="]rpm with the throttle just cracked open, but it's different as you run at the[/FONT][FONT="]same throttle position and 9k rpm, then fiddle with the air jet. If it pops and[/FONT][FONT="]stuff on closed throttle decel, then play with the mixture screw and slow fuel[/FONT][FONT="]jet.[/FONT][FONT="]And beg, borrow, or steal a filter mask with hydrocarbon filters. And spend the[/FONT][FONT="]~$25 on some Howard Leight Thunder 29 hearing protectors, or whatever the[/FONT][FONT="]spiffy headphone looking things are that MSC has. Don't skimp on those. Then[/FONT][FONT="]wear earplugs under them. At the end of the day, you'll be glad you did.[/FONT][FONT="]And take notes. Write down your thoughts. Write down 'sputters' or 'bogs' or[/FONT][FONT="]whatever you want, as long as you put your ideas down right then and there.[/FONT][FONT="]Don't try to remember what it did five runs ago. If nothing else, they'll look[/FONT] cool in your notebook when you go to the racetrack.Jetting Your Slide Valve Carburetors
All Keihin carburetors are pre-jetted for bolt-on operation. Carburetors are jetted using stock motorcycles and watercrafts. Any major engine modifications like higher compression pistons and racing exhaust systems may require minor jetting adjustments. The following is a guideline for jetting Keihin carburetors. Perform the jetting in the order given below.
1) Correct Float Height
Before changing any jetting parts, check the carburetor floats for correct height. Measure the height from the bottom of the float to the Throttle Opening. carburetor-body gasket surface. Correct height can be found on the chart. When checking the float height, the float should be resting, but not depressing, the spring-loaded float valve pin. This can be done by tilting the carburetor until the float tab just makes contact with the valve pin. If adjustment is needed, bend the metal tab on the float arm until correct height is obtained.--see example #1
Float Height
FCR
CR
PWK
ALL
ALL
28
35-39
PWK
ALL
ALL
28
35-39
NOTE:(See Jetting instruction #1)
for correct pressure
2) Idle
Set idle speed to proper r.p.m, by adjusting the IDLE SPEED SCREW. Turn the IDLE MIXTURE SCREW or the AIR SCREW to for correct procedure, achieve highest speed and best response. The IDLE MIXTURE SCREW (FCR) controls fuel delivery to the idle port and the SCREW is located on the engine side of the carburetor slide. Turning the IDLE MIXTURE SCREW out will make idle and off-idle richer. Turning IDLE MIXTURE SCREW (CR, PWK, PJ, PE) controls the amount of air to the IDLE and SLOW CIRCUIT. This SCREW is located on the air cleaner side of the throttle slide and turning the SCREW out will lean the mixture and turning the SCREW in (clockwise) will richen the mixture.
3) Off Idle To 1/4 Throttle
The SLOW JET and SLOW AIR JET are most effective in this range. When you want a richer mixture in this range, use a larger SLOW JET or a smaller SLOW AIR JET. The opposite holds true for a leaner mixture.
General Jet Needle Changes
4) 1/4 TO 3/4 Throttle
The JET NEEDLE is the most effective component in the range. Changing the STRAIGHT DIAMETER (D) will change the calibration in the transition range from the SLOW circuit to the MAIN circuit (1/8 to 1/4) throttle. A smaller diameter will make this range richer and a larger diameter will lean this range. TAPER (A) changes are only made if there is a problem balancing the calibration between 1/4 and 3/4 throttle. If the mixture is rich at 1/4 throttle and lean at 3/4 throttle, a JET NEEDLE with a larger taper is needed. If mixture is lean at 1/4 throttle and rich at 3/4 throttle, change to smaller taper. If the calibration is lean from 1/4 to 3/4 throttle, raise the JET NEEDLE by lowering clip position, or use JET NEEDLE with shorter length (L1). If the calibration is rich, lower the JET NEEDLE with a longer (L1).
5) Wide Open Throttle
Changing the MAIN JET affects this range. Select the size of MAIN JET which offers the best W.O.T. performance, then install one size larger MAIN JET for ideal engine durability.
6) Accelerator Pump (for FCR)
In normal applications, the ACCELERATOR PUMP should not require any adjustment. If a rich stumble occurs as the throttles are opened, the ACCELERATOR PUMP timing can be delayed by widening the gap on the ACCELERATOR PUMP linkage where it makes contact with the plastic lever. Reducing the gap will cause the ACCELERATOR PUMP to deliver fuel earlier.
7) Throttle Valve Cut-Away
(FOR CR, PWK, PJ, & PE) THROTTLE VALVE CUT-AWAY will influence the calibration in the area of 1/8 to 1/4 throttle. What the CUT-AWAY does is change the air velocity over the MAIN NEEDLE JET which changes when the MAIN SYSTEM begins delivering fuel. If the transition is lean change the throttle valve to a valve which has less CUT-AWAY (lower number). If this range is rich use a throttle valve with more valve CUT-AWAY (higher number).
Jet Needle Changesfor FCR Needles
35-41mm
Contribution of Jet Needle
Note:
Simply change the clip position, lowering or raising will allow you to make adjustments. A shorter needle will be richer and longer needle will be leaner. The mixture richens when the jet needle is raised and leans when lowered.
:confused2:
Last edited by a moderator:
Rick52
Well-Known Member
I suppose a good tuner can make anything work properly and work well. I ran the PCW 39mm FCR on my 1200, 1260 and 1500 and never had to do any tuning and adjustments. Each Spring I took my bike to a race tuner and each year the carbs were dead on. The carbs were dead on out of the box. I checked the A/F on the PCW 39mm out of the box and they ran 12.8 to 13.2. I have had to change the needle positions when changing exhaust systems. Stay away from anything bigger than the 39mm, your torque loss will be Significant. I dont care what carbs or EFI throttlebodies you use. The 41mm 43mm and 45mm are just too big. EFI is way too expensive for a self management system. Yes, a properly tuned 35mm Mikuni carb set willgive you all you could use. The stock heads cannot flow enough to justify any serious carb mods. Stage 7 is all you need and a good tuning. imho rick rash
