carb sync screw all the way in

[vladthedog]

I've been looking around the forums for about an hour, because I know my question has been asked before. I'm sure I'm just not using the right search terms.. so sorry for the repeat

I am syncing my carbs for the first time. I am using the weber sync tool that sits on top of the carb (bike has stage 7 done by previous owner, no vboost). I bumped up the idle a bit, and then looked at each cylinder, and it was out of sync. I start moving the screws in and out to just see how it all worked. Then I started actually sycing. I got it pretty well synced up, but noticed that the screw syncing cylinders 1 and 2 is all the way in and it barely gets synced. Carb 2 is sitting at 7, and bringing in that first screw all the way in tight, carb one is sitting at around 6.9. carbs 3 and 4 are synced to right at 7.

My question is simply, since its in all the way, what do I do to get it "more" synced? Do I have to adjust the linkage between the screws, and if so, how do I get it "balanced" again?

Thanks

 

[davesax36]

Do you have a vacuum leak somewhere in the system?

 

[ninjaneer]

when you say "no vboost" do you mean to say that it's been disabled? it's a common thing for folks to disable the servo when the butterfly valves open. however, by doing so, it makes synching very difficult, if not impossible.

 

[tugla]

could have the sync tabs bent ....they bend easy....adj them a bit so each of the three scews are doing something when you turn them.

 

[Rusty McNeil]

If I'm following you correctly then I'd say maybe bend the tabs between carb 1 & 2 to change range of adjustment ( Although I've never heard of anyone having to do this.

A second possibility is that the connecting linkage between carb pairs was not assembled right.

Vacuum leaks can be an issue as well and is something to be eliminated first before you go bending stuff.

If you have to bend them I would guess your going to have to remove the whole rack and do a mechanical synch to adjust those tabs.

I've never used the Weber, does it work on Vacuum above the carb or just air flow measurement into the carb?

And either way I'm not sure how that is effected by vacuum leaks as opposed to how vacuum leaks will definitely screw up readings on a motion pro tool.

I would think with open Vboost a vacuum leak would effect carbs 1 & 2, or 3 & 4 equally since both carbs would have equal access to that leak, making a vacuum leak not have as much effect on carb balance for that pair?

As for Vboost disabled, are the replacement cross over tubes from DJ installed or has the Vboost just been disabled and left in the open position?

If the Vboost butterfly's are still there but disabled you should be able to figure a way to close them and then synch it.

I don't know why anyone installs those replacement crossovers, making synching a huge pain in the ***.

Trapping or wiring the stock Vboost permanently open works just as well and leaves you the option of closing them for synching.

On mine, when I ran it open all the time, I removed the controller and servo and used a throttle stop pinch screw on the cable to hold it open, easily letting it be closed for synching. I put it back to normal on my new motor, it didn't like open Vboost at all.

On the Weber how significant is the difference your seeing, I think you said 5.9 versus 6.0?
What's the full scale from 0-?
Maybe your imbalance isn't that significant depending on the scaling of the tool?

 

[SFCMcGan]

when you say "no vboost" do you mean to say that it's been disabled? it's a common thing for folks to disable the servo when the butterfly valves open. however, by doing so, it makes synching very difficult, if not impossible.

.

 

[dannymax]

It isn't all that unusual to find a bottomed out sync screw, I've run across it several times. Side impacts, or even just a fall off the side stand can cause this, I've always felt Yamaha built this 'gross adjustment' into the carbs to allow for variances in production but that's JMO.

Yes a tab probly needs to be tweaked....figuring out which tab, how to access it and what tool to use to bend it is another story tho, you will have to study the sync mechanism to figure it out.

Usually the carbs don't need removal and the 'tweakage' can be performed with them on the bike.

If you can provide a good clear pic I might be able to point you in the right direction.



EDIT: A couple tips tho....it will be the tab that the bottomed out screw pushes against that will need bending.....remove that screw completely before doing any bending, that will give you a little more room to work. Also, opening the throttle wide open may rotate the tab to a more favorable position....good luck.

 

[vladthedog]

Sorry, bit more info. I'm a new owner of a 2000 vmax (bought it a month ago). in very good condition. Previous owner did some mods (I think mark's exhaust, plus stage 7). didn't have any leftover parts, so I am stuck with whats on the bike, until I get around replacing it.

- vboost was completely eliminated. no butterfly valves, etc. Has the replacement crossover tubes.

- the weber sync tool is one that sits right on top of the carb intake, and measures actual air input.

- weber sync tool measures from 1-30. so 6.9 vs 7 is not too big a deal.

- I don't *think* I have any vacuum leaks. Even before the sync the bike ran very well, and the little i ran it last night after the sync, it runs great. What can I look for for vacuum leaks?

- I'm not concerned with making it more in "sync" right now. Just worried over time since I've already tightened the 1&2 screw, it will just get more and more out of sync.

Is there a diagram somewhere for how the linkage is supposed to be set up? I've flipped through my book (forget brand, but one of those thick books with pictures), as well as online.

I will get some pictures shortly.

And BTW dannymax, love your quote in your sig

EDIT: Attached are two pics. i know they aren't the best, but don't think I can get better without taking more off (and about to go for a ride). in the first (taken from the side), if i understand correct, the tab you are talking about is the "back" one (if starting at the head of the screw, its what is on the opposite end, behind the middle tab with a spring in between it and the middle tab?)

EDIT 2: actually, re-reading your last post, it sounds like you are saying its the middle tab that is potentially the problem? if thats the case, would it need to be bent slightly towards the head of the screw?

 

[dannymax]

EDIT 2: actually, re-reading your last post, it sounds like you are saying its the middle tab that is potentially the problem? if thats the case, would it need to be bent slightly towards the head of the screw?

This is correct, the middle tab....the one (and only tab) going to #2 carb (the rear carb)

Remove the screw, open the throttle (hopefully that places the tab in a better spot to access it) and bend the tab towards the screw you removed.

 

[vladthedog]

Before I start bending things, is there anything else I should look at/be aware of that could potentially be causing my issue? I've never done this syncing thing before, so not sure all the details. I would assume that if all 4 carbs are pulling same amount of air, sheen they are in the "right"spot (I.e. it's not like if I backed out all 3 screws X amount of turns I would still be in sync, but have more wiggle room)?

 

[naughtyG]

All the sync does is make sure the butterfly valves in each carb open and close exactly together.

So, you should be able to set them pretty close on the bench just by looking down the carbs and making sure they're close. That should help you see if there's a way to get them close without the sync screws being all the way in - if you can't then the tabs need bending.

 

[bumper]

I use to use a business card and set it just so it slipped through at the same pull. You have to turn the idle screw up when doing this and then when done back down. It gets them pretty close.

 

[Fire-medic]

I use to use a business card and set it just so it slipped through at the same pull. You have to turn the idle screw up when doing this and then when done back down. It gets them pretty close.

I recall some two-strokes used to spec a certain drill size (yes, a very small drill size) to be between the butterfly & the body for a set-up. I also was shown the trick of using needles or toothpicks inserted the same-distance into the butterfly/carb body space, and then comparing the angle each needle assumed, as a way to synch w/o a Carb Tune or other fluid-medium. A crude method, but it would get you into the ballpark.

How-many of us have used a cellophane from a pack of cigarettes to set the release (opening) point when setting a set of points (or two)? How-many even have owned something having points? I still have a small flexible hex wrench for setting the points dwell thru the slide-up window on a GM distributor cap, and an offset distributor nut wrench.

 

[m-cman]

How-many of us have used a cellophane from a pack of cigarettes to set the release (opening) point when setting a set of points (or two)? How-many even have owned something having points? I still have a small flexible hex wrench for setting the points dwell thru the slide-up window on a GM distributor cap, and an offset distributor nut wrench.

Just finished doing that on a friends 1971 XS650 getting it ready for the Mid-Ohio event in July. Did all the old stuff, new points, plugs, condensers, coils, set timing and dwell, etc. Been a long time since I had done any of that. Had to use something besides cig wrapper though. Nobody I know smokes anymore. Was kinda fun... :clapping:

 

[dannymax]

Just finished doing that on a friends 1971 XS650 getting it ready for the Mid-Ohio event in July. Did all the old stuff, new points, plugs, condensers, coils, set timing and dwell, etc. Been a long time since I had done any of that. Had to use something besides cig wrapper though. Nobody I know smokes anymore. Was kinda fun... :clapping:

Hearing some terms I haven't run across in quite awhile! unk:

 

[Traumahawk]

Hearing some terms I haven't run across in quite awhile! unk:

My old 71 Plymouth satellite sebring, had a 318 with points. 18 thousandths if I remember right, or a matchbook cover, which ever one you had.

 

[tugla]

paper clip used to set point gap....match book also...bush tools are the best lol..