OEM Carbs? Post your setup

ya for sure the mileage is all highway driving and staying out of the vboost. in town is more in the 30's.....
the stock plugs work great aand there are a few guys on the forum that do carb overhauls that will do wonders for the bike..

tugla said:

the 1420 I'm sure drinks the juice but should be ableoto get better mpg a bit

Click to expand...

I did a pure highway number test this last weekend. Having filled up and made a uninterrupted run across Houston at 75-85 mph.

The bike did 31 mpg on a 1540cc, 13:1 CR stroker motor. Still running OEM carbs.

That's with the venture 5th, turns 4000rpm at 80 mph

Not finished tuning yet though.

Old setup was easy 37-39 mpg on a pure highway run at 75-85 mph, and low 30's when beating the crap out if it.

Rusty McNeil said:

I did a pure highway number test this last weekend. Having filled up and made a uninterrupted run across Houston at 75-85 mph.

The bike did 31 mpg on a 1540cc, 13:1 CR stroker motor. Still running OEM carbs.

That's with the venture 5th, turns 4000rpm at 80 mph

Not finished tuning yet though.

Old setup was easy 37-39 mpg on a pure highway run at 75-85 mph, and low 30's when beating the crap out if it.

Click to expand...

that's awsome for that size of motor.....what did u chg that your bringing it back up the mpg.

I don't know my carb setup, but my first two refills at around 80 mikes and just over 100, have yielded 44 and 46 mpg respectively. Mixture of some hard acceleration (with v-boost) and cruising at 80-85

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Altitude 550ft
Airbox lid modified to hold a flat panel K&N
Air correctors
170 Main (Mikuni)
#40 Pilot fuel jet
Stock PAJ 1&2
Slides Drilled, Stock springs I think
UFO StreetPro 4-2 w/slash cuts
Needles on 2nd notch from blunt end
Screws out 2.5 turns
Functional Vboost
Mileage 32-37

I know there's room for improvement and its been suggested to drop to a 150 or 155 main jet (Mikuni) and move the clip to the 3rd notch.

No Altitude
VooDoo 4-1 Exhaust w/ Supertrapp (8 discs)
Airbox Lid Replaced With Air Filter (air correctors)
165 Dynojet Main
Stock PAJ 1 & 2 (Mikuni 100 & 175)
Stage 1 Needles clipped on 1st Groove
Stage 1 Springs
Slides Drilled
Brisk BR12ZC Plugs
Vboost Stock
A/F Screws out 2 1/2

Getting 32-35 MPG

from experience I'd chg back to stock needles shimmed and get mileage higher....better yet seans set up.....dj stg 1 needles seem to be just more of a pain to set up vs other needles....just my 2cents....

tugla said:

from experience I'd chg back to stock needles shimmed and get mileage higher....better yet seans set up.....dj stg 1 needles seem to be just more of a pain to set up vs other needles....just my 2cents....

Click to expand...

Stage 1 Needles were installed by the previous owner of the bike so I have been trying to make them work. It has been running good since I dropped the main and moved to the 1st groove but still rich at the idle. I am going to fuss with it a little more and then I might have to make that change. Thanks

Here's where I am right now, with a minor bobble in the 2500-3500 rpm range, and the main yet to be verified. More on that in a second....

Alt. 700' with average Temp of 80* and humidity of 70%
Stock 2003 V-max
Stock air box with the Y removed and a K&N filter of OE shape
UFO Dragstar with the slash cut muffler, huge core
Dynojet Stage 1 jet kit with extras

Main jet - DJ 175
Needles - DJ stage 1, 5th clip position from top
Pilot air jet - DJ 165
Pilot air screws - 2.75 turns out

Now before anyone says "throw away that stage 1 kit", save it. I've been tuning my own bikes for 27 years and I know how to use a jet kit. In my assessment, folks that make that remark have either never used every option in the kit, or they have concocted their own answer (like me). My reasons for keeping the kit is that I have an affinity for the stock air-box. I do, however, think that Dynojet dropped the ball on this kit by not exploring more aggressive options with the stock air-box. Plain and simple, they designed it for a paper filter and moderate pipe, then they did a leap frog move to the stage 7 kit for all out performance. I'm that guy that tech support won't talk to because I want to be in the middle.
I have been tuning in 60*-70* air, with very low humidity because I do ride in winter and want to make sure I don't lean out into a dangerous place when it's 28* outside with 10% humidity. I will pay a penalty on a hot summer day, but who doesn't? Right?
My experience in this tuning session, with the Dragstar and K&N, in the conditions above, is that I was too lean with any of the provided main jets, and only started getting where I wanted to be when I lifted the needles WAY up to the 5th clip position. On a clear, dry night, this thing was screaming with the 170 main jet, but still too lean according to the spark plugs (ethanol complicates this). I also found a flaw in the Jet Kit note that advised installing the DJ 150 pilot air jet to deal with a hesitation going to WOT after a steady cruise. It was very much overkill. FYI, the DJ 150 PAJ is a great deal smaller than OE. Also, note that the PAJ is the same type of jet used for the main jet.
My answer was to order an assortment of jets from Dynojet so I could continue to richen the main and have more options on the PAJ. The kit included DJ 150, 160, 165 & 170 jets. I ordered DJ 155, 175, 180, 185, & 190. This gives me the same jets provided in the stage 7 kit, plus the DJ155, 180 & 185. I also ordered the air corrector jets from the stage 7 kit. Dynojet won't sell the stage 7 needles, but I don't think I will need them anyway. The assortment is a bargain from DJ, $50 shipped (about $2 a jet).
While I was waiting for my order, I did some testing with what I had. With the DJ170 main (slightly lean on top) and the DJ needle in the 5th position, I had a really strong pulling bike, but a terrible hesitation. If you compare the OE PAJ to a Dynojet jet, it is very close to a DJ170 or DJ175, and the kit advised dropping to a DJ150 for that hesitation. This resulted in a terrible sputtering bobble instead (too rich at the transition near 3500 rpm). Looking at a comparison of DJ jets and Mikuni jets on a chart, the DJ165 that I had already discarded from the main was a mid-point for the PAJ. Now running the DJ170 main, DJ needle on the 5th, and DJ 165 PAJ I was pulling really hard with only a slight lean condition on top and a minor bobble when cruising at 2500-3500 rpm, and that hesitation going WOT from cruise became a very brief pop/bang hiccup.
When my extra jets came in, I made a classic mistake of changing more than one thing at a time, over confident that I could predict the outcome. I tried to return to the OE PAJ, raise the needle to the 4th and up the main to the DJ175. That was dumb. Too lean in the middle, crap idle, sounded like ****, yada, yada. There was really only one known change needed. I was slightly lean on top, so I kept the DJ175 main to address that, and reverted the PAJ to the DJ165 and needle clip to the 5th position. That is where I am now. I am rained out for a few days, so validation of the main jet awaits, and then I will be looking closer at the PAJ. I am undecided on the need for the air correctors, but doubt they come into play with the air-box installed.
Moral of my story? Remember not to put the cart before the horse (tune the main first, needles second, pilot circuit third), and a jet kit is not junk just because I go out of the bounds of it's original design parameters (with care, it can be augmented to work very nicely).

I do intend to get some dyno time after I settle everything to validate my A/F ratio across the powerband. It's possible that I am overly optimistic about the cool air in Central Texas and all this is one shade too rich. (I suspect I will be shimming the needle to a mid-point between the 4th & 5th clip positions) If that's the case, I may well find that DJ170 is correct. The V-max does like to run lean! By the way, I sent my buddy out on a country loop around my shop where he could wind her up. He was nearing 140mph on the longest straight with only cows and corn in the 3/4 mile between that stretch and my shop. It sounded like a cup car at Texas Motor Speedway! I'm diggin' it!
To be continued....

Scotty,

I am not at elevation so that changes everything. I had a Stage 1 DJ kit installed in my bike when I purchased it. The owner had DJ170 mains and Needles clipped at the second groove. He had 20 discs on the Supertrapps. This bike was so Rich, the entire back of the bike was covered with black soot.

I dropped the mains to DJ160 and moved the clip to the first groove making the needle as long as possible and she is running strong but still cant get rid of the slightly rich condition. Just as TUGLA stated above, I have concluded that the flaw with the Stage 1 kit lies with the needle. If you compare the needle to all others (stock, Stage 7, FP), they are very short so you are never completely on the needle which results in the bike running rich at the low end. To actually make the Stage 1 needles work, I think a small main is required such as DJ155. However, I bet you would end up lean on the top end with a DJ155 so a Rich idle it is for now. That's kind of my experience.

Without knowing every detail of your combination, it's hard too get to specific about any opinion on your tune, but I think I can lay out some relationships that most folks miss (including Dynojet, to some extent).

To say that a bike is running rich, you must qualify with further specifics. What rpm? Cruising around town? Most folks that see lots of soot in the pipe are not getting it on the main jet, but on the idle screws or the needle.
Here's the deal I have uncovered: Freeing up air flow with a filter and pipe (plus low altitude, dense air) created a need for more fuel. I was able to add enough fuel to make a difference with the smaller jets in the kit, and by raising the needle way up. It was possibe to tune the idle and mid to make it feel great, but reading plugs still said I was lean. Here's what was really happening....
I bought the bike all stock. The only mod I found was that the plugs had been removed in order to tune the screws. It started well when cold, at most any temp. Ran good, but my buddy commented he could smell my exhaust when we were cruising at lower rpms. I found that the screws were 6 turns out, on a stock bike! The previous owner lives nearby, at a still lower altitude. I suspect that they wanted it to start off-choke even when cold on warmish days, so they enriched the heck out of it. Why does this matter? Because when I started modding exhaust and intake, I started adding more fuel to this really rich idle. (The main jet does add fuel at the bottom, it just doesn't have primary control.) The larger the main jet got, the less turns out on the screw I needed. Now, the reveal came when I was trying to fix a lean pop in the middle. I followed-the note in the DJ kit to switch the PAJ down to the DJ150. Here's the deal with that. It took more air away from the idle, further enriching things to where I was down to one turn on the screw. As the main went up, what the idle really needed was more air, placing me back in the middle of the adjustment range on the screw. Today I found that a near stock PAJ was very close with the DJ175 main. Confirmation of this is in the stage 7 kit where they suggest a DJ190 PAJ, noteably larger than stock (adding more idle air for the very large main, the stg 7 kit comes with a DJ175 main...)
To simplify what I'm saying, you can only go so big on the main before the idle air is insufficient. Most folks interpret this low end rich condition as excessive main jet. They compensate by leaning the screws and the needles, as your bike had, never exposing the lean condition up high. The Vmax really likes to run lean. It is very tolerant of lean conditions in small doses. How many people do you know that will hold 8500 rpm for several minutes? I know pro road racers and drag racers that won't see that. If you have masked this lean condition with compensation tuning on the bottom/mid range, then even in a drag race you will pull from 4k-5k on up, shifting at 7k-9k, falling back onto the upper mid-range with each shift. That lean condition is hard to detect. You cruise the return road or around town with the richer bottom end and soot up the pipe and plugs to hide it. Properly tuning the PAJ is key to matching the low end air to your top end tune. Both Dynojet kits skip over this with a mere band-aid, probably because few of their users are really getting the max out of their combination, and fewer still actually tune to the highest degree. (daily drivers must compromise for season to season use)
I believe frustration and lack of knowledge lead most to scrap the kit., and these are the things behind that frustration.

Now I did get more testing in today after the weather cleared out. It was about 10* warmer than what I had been working in, so that would mean I am a little richer than my last outing. I also upped the main to the DJ175, richer everywhere... It was obvious because it started loading up, not at high rpm, but at idle, as I decelerated to stop at a light. This was my queue to add more idle air by bumping the PAJ from the DJ165, to a DJ180. That's a shade smaller than OE. The next test ride was marvelous! For the first time I was able to pull every gear from 2000 rpm, to redline without a hiccup, and it was smooth around town. Cruising at 3500 has the slightest suggestion of a rich bobble, and the idle mixture needed to be leaned out. I dropped from 3 turns to 2.25 turns.
This is making me think I am flirting with a slight rich condition at warmer temps. I need to get a plug reading at 8k-9k in warmish air to check the main. If it's good, I need a little more air in the PAJ, so I'll go to a DJ185 (DJ190 was the suggested size with a stage 7 kit), and fine tune the needle with a shim to sit between the 4th and 5th grooves (4th groove is the start for the stage 7 kit). If the main jet is slightly rich, I'll drop back to the DJ170 and reassess the needle and PAJ after. (I realize the stage 7 needle is different from my stage 1, but not by much. The stg 1 needle is pretty thin already.
I have tuned and raced bikes for years (aside from the last few where my wife was fretting), and I have had great success with factory air boxes. My buddy that used to race F1 superbikes used pod filters on his 1978 GS1000 and was competitive in 1984 with newer bikes, but by 1990 he wouldn't take an air box off his 1340cc GSXR for anything. Designs improved. I think I am getting better air, if not more, from the stock air box on my 1200 Vmax. This is because the K&N (that Dynojet advised against with stg 1) flows so much better than stock elements, and the OE velocity stacks make for smooth, and therefore denser intake air. Do the math on the filter pods surface area vs. the OE filter area. (only a concern at max rpm) I think there is little difference, so with a gauze media filter, my penalty is limited to the Y on top of the air box (the one Dynojet blamed for my mid-range air concern). I ignored them and left it off. Now I am tuning in the same vicinity as the stage 7 kit. The science says that if I am burning the same fuel as a stg 7 kit, at redline and with a proper A/F ratio confirmed by plug reading, then I must be moving a similar amount of air at redline.
Instead of dropping the main and needle, try adding more air down low with a larger PAJ. This would be further appropriate at higher altitudes where air is less dense. I bet you have room for a larger main jet and the power that comes with it.

My revised tune.....

Alt. 700' with average Temp of 80* and humidity of 70%
Stock 2003 V-max
Stock air box with the Y removed and a K&N filter of OE shape
UFO Dragstar with the slash cut muffler, huge core
Dynojet Stage 1 jet kit with extras

Main jet - DJ 175 (slightly rich?)
Needles - DJ stage 1, 5th clip position from top (slightly rich)
Pilot air jet - DJ 180
Pilot air screws - 2.25 turns out

I ran as lean as 147.5 mikuni's at sea level. Woke the bike up a lot.

I made that decision after leaning it out for Utah-Wyoming altitude, installing 145's
When I got it home (Houston, elev. 15-25') from that project and unloaded from the trailer and took it for a spin it was was unbelievable how great it ran with the 145's in it. So I bumped it up to 147.5's in light of the new low altitude and never looked back.

That was with the stock airbox, K&N filter, and stage 1 needles on what clip I don't remember any longer.

Its pretty difficult to go too lean with the commonly available jets in my opinion.

I'm on the home stretch now. The DJ175 proved to be the correct main jet in 75* weather with low humidity. That left things a bit rich with the clip in the 5th groove and the DJ180 pilot air jet. It was loading up and trying to fuel foul the plugs anywhere under 4k rpm, but was showing signs of being too rich anywhere below 6.5k (verified by plugs), so I dropped the needle a half notch by putting the clip in the 4th groove and a shim below the clip. I also took a big step to the DJ190 to see if I could make the bottom end too lean on purpose. Mission accomplished. The mid-range smoothed out beautifully with the change on the needle, and I had a lean flat spot just off idle, to about 3k rpm. Any bobble between 3500 and 6500 was gone and a roll-on from steady 3k-4k was hesitation free. I am splitting the difference on the PAJ now with a DJ185, which is maybe one Mikuni size above (leaner) stock.

Rusty, I started this misadventure with the Dynojet provided sizes and was very definitely too lean in 60* weather. It was causing lean misfire and blistering the plugs using the DJ160 and DJ165 with the needle in the recommended 3rd groove. It only improved when the needles were raised to the 5th groove. That is indicative (now proven) of a lean condition on top, with the overly rich needle position masking the problem. It is essential that the main jet be dialed in before anything else. The Vmax is an odd duck with it's Jekyll & Hyde personality. The fuel curve gets so steep that tuning the pilot air jet is necessary to blend the transition from it's very mild low end. As usual, every scenario is different, but I hope someone finds my details useful.


Alt. 700'
Stock 2003 V-max
Stock air box with the Y removed and a K&N filter of OE shape
UFO Dragstar with the slash cut muffler, huge core
Dynojet Stage 1 jet kit with extras

Main jet - DJ 175
Needles - DJ stage 1, 4.5 from top (clip in 4th w/ shim below clip)
Pilot air jet - DJ 185
Pilot air screws - 2.5 turns out

One more test ride to confirm the pilot air jet.....

EDIT: Yee Haw! Chester is dead! I think I'm done!
The tune above is just nearly as seamless as stock (if you plug your ears and ignore the loud noise from the pipe).
With a few hours cooling off, and a new set of plugs, I had to start it on the choke with a cold motor, got off the choke in under a minute, still idling low since it was cold. Pulled away with no hiccups. Warmed to operating temp on the way out of the neighborhood, cruising at 3k rpm. No surging, no spitting. Turned onto the highway access road and pulled off to let traffic clear. When I had the road to myself, I executed a WOT pull in each gear, from 2k to redline. No issues, and only normal lugging in 4th & 5th starting from such a low rolling speed. Next I performed a WOT roll-on from a steady cruise at 3k, up to redline, in 2nd & 4th. No hesitation, No pop-bang launch. Nice and smooth acceleration. After I turned back the other way to have a couple of miles to myself, I launched from a near stop, WOT through every gear, shifting 8k, up to a blink past 140 mph (kinda harry with a 10-15 mph wind coming from a little left of head on). Finally, I coasted back down into legal territory and got hard on the brakes with full downshifts like I was about to miss the last exit for a Frito Pie. I was expecting a lean stall as soon as I came to a stop, but it didn't happen. I repeated most of this a couple of times, then took the long way back to the shop at 45 mph, 3k in 5th, a little more in 4th. Nothing but a stable hum under a very light throttle cruise. More of the same when I dropped a couple of gears to hold closer to about 4500 rpm. I rolled up to the shop and turned it off, then tapped the starter for a quick restart. I pushed it inside and pulled the plugs. Nice hint of tan on the ceramic insulator, nice heat zone on the electrode, only a hint of black around the outside wall. Excellent!
I am going to leave it alone and put some miles on it to see how it behaves at different temps. Tonight's test ride was at 62* and 53% humidity. I expect this will be a great tune for anything 30* higher or lower. We'll have to wait and see how it does on a truly hot day. Fortunately, my air density calculator says it will need to be VERY hot to matter....

I'll report back after I get some dyno time to check the A/F curve.

scottybaccus said:

As usual, every scenario is different, but I hope someone finds my details useful.

Click to expand...

I did find ScottyB posts useful:

I was planning on going with a smaller main (going to go to a Mikuni 147.5 from the DJ160). However, after reading the posts from ScottyB, I decided to try a larger PAJ2. So I ordered a set of Mikuni 175s and 147.5s (just in case)

I replaced the 170 PAJ2 with a 175 and of course everything is different. I was actually lean low thru midrange. However this was a nice change from always being rich.

I shortened the Stage 1 needle by moving to the 2nd groove (I was on 1st groove no shim). Then I was able to use the A/F screw to richen the idle and we are very close. I might still lower the main to 147.5, but with 175 PAJ2, I am tuned the best I have been. The bike rips 2000+ RPM's.

No Altitude
VooDoo 4-1 Exhaust w/ Supertrapp (8 discs)
Airbox Lid Replaced With Air Filter (air correctors)
165 Dynojet Main
Stock PAJ 1 & 2 (Mikuni 100 & 175)
Stage 1 Needles clipped on 1st Groove
Stage 1 Springs
Slides Drilled
Brisk BR12ZC Plugs
Vboost Stock
A/F Screws out 2 1/2

I had the chance to connect an Innovate LM1 (with LM3 box, vacuum and RPM curves) to the Max, so realised that the Stage7 installed on my bike was not a good idea :

1995 Vmax
Stock headers with Strapps (10 discs) mufflers
Dyna3k ignition Box (cuve 5)
Carb set up, :
Dynojet stage 7 with 3" velocity stacks, Vboost alwayw opened.
-Main fuel jets, 147.5 MK (before it was 175 DJ!!)
-Stage7 needles, second groove from top
-Stage7 springs.
-Slide drilled.
-Factory Pro HDR Needle jets
-170 MK PAJ2
-Stock French PAJ 1 : 95
-Stock French idle fuel jet : 42.5
-Fuel mixture screws at 3 turns.
-DJ air restrictors.

Before Wideband tests, main jets were 175 DJ and needles were on third groove.
Bike was running good at high RPM, WOT was lazy at midle RPM.
Sure it was at 9.5 AFR at 4000 rpm and 10.5 at 8500 !!

With 150 MK Mains jets it was about 12.8 at 9000 and 12 at 4000.
I have no more the innovate unit but with 147.5 it should be around 13 AFR at high RPM and 12.5 at middle.
Engine response is crisper everywhere now!

Finally it seems that Stage7 with stock headers is not a good idea using only DJ parts...

Ok folks, i have almost the equipment that scottyb has listed 3 posts up (UFO Streetpro 4-2 & Morleys style air box being the differences in equipment). My question is would his carb tuning thats listed above work for me? Im also at 600' elevation instead of the 700' hes at so i dont know how much that would change things if at all. Any help would be greatly appreciated!!

Edit: Talked with ScottyB and got some great advise and help with my tuning, got me damn close! Just did some final adjustments to things and now she's running like an elephant ***** ape! If only I could find a dyno in my area to get some numbers and see if there's any room for improvement...

Here's the current setup:

UFO StreetPro 4-2 w/slash cuts
Morley style airbox
Air correctors
PAJ2: 177.5
PAJ1: Stock
PFJ: Stock
Main Jet: 162.5
Slides drilled
Stage 7 needles on 4th clip
AFR screws: 2.5 turns out
Elevation: around 600'

(Jet sizes are all Mikuni, all adjustments made and work peformed with the aid of Arrogant ******* and Double ******* ales, no apes were harmed in the process.)

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This isn't final........but is anyone's?

Sea level

UFO headers, triumph Daytona carbon mufflers
Morleys muscle kit
Slides not drilled
Stage 7 springs and needles.
157.5 mains
5th clip from blunt
3 turns out
Vboost opened

I

G`day All from Australia,

Firstly, all the evidence points to losing 10Hp with the VMax & Cobras combo... I get that, so, moving on..... I like the look and the sound and would like to persevere with them regardless.....

Anybody like to share your past experiences (preferably as found on the track or Dyno) trying to improve the Cobras??

Certainly there seems to be plenty of Dyno proof that they loose power, BUT, does anyone out there have any positive (sensible) Dyno or Track proof of changes made to improve the Cobras (even by a small amount....) for instance carb tuning etc...

Many Thanks in advance of any and all contributions.....

Best Wishes from Australia....