Stage 7 carb sync question

[Daremo]

So I bought an awesome, lightly modded 85 Vmax last summer for something to work on. I will preface that I didn't really know anything about it other than it put a huge grin on my face the first time I rode it and I had to have it. From browsing the forum over the winter/spring and the process of elimination I have discovered that it has a Stage 7 jet kit and a 4 into 1 custom exhaust(no emblem but it looks for all the world like a Yoshimura can). I cleaned it up, threw some new paint on the bodywork, cleaned the air filters and oxidized electrical connections, changed the oil and battery, etc and have been riding it around and enjoying the hell out of it while at the same time dealing with the little gremlins that pop up on a 24 year old bike(this forum is a lifesaver I will say). It starts right up most of the time, idles well and pulls pretty hard at around 70-80 degrees. Runs crappy if it's colder than that and runs ~fantastic~ if it's above 90. On sustained freeway cruising it seems to have a flat spot where it falters and hesitates at around 75/80 mph(between 4 and 5K) and will not stay steady. Under this it seems okay, over it pulls hard again but still seems to be choked off/starving. This is less noticable when it's hot out and gets a lot worse when it's colder. Before I start ripping things apart(not a carb guy but I can learn and I have another bike that runs anyway)I thought I would try simple things like checking for leaks, pea shooting it and also syncing the carbs.

Sorry for the long preamble but my actual question is this: How do I sync the carbs with the Stage 7? I searched fairly exhaustively and it sounds like since the v-boost appears to be gone(I have nothing with a round connector on it under the left air scoop) that the carbs are linked and draw(?) together and thus can't really be separately synced. Can this be done with a Carbtune? Any help anyone can offer would be greatly appreciated!

 

[naughtyG]

What you want to find out is, had your actual Vboost been completely removed, or have the Vboost butteflies just been stuck in the open position? If they are still there and you can just manually close them, then you're good for syncing.

If you remove the H covers on each side of the carbs, you should just about be able to see the Vboost below the carbs, and whether the butterfly valves are still there. If not, removing the carbs isn't that hard, and once they're off you can tick your fingers in and feel for those valves.

Check out the carbs/and tuning subforum as it's got lots of good info on all things carb.

Not sure about the temp thing, but our carb gurus will chime in for sure

 

[gamorg02]

bike will run richer as the ambient temp gets hotter. sounds to me that a shim in your needle would do the trick or depending on the stumble, moving the eclip a notch.

But before u do that, does it stumble there if u do a full WOT, or cruising, or both?

 

[Daremo]

Interesting, will pull the covers off and check that. So is the missing piece under the cover just a solenoid then? Thanks for the info!

On the stumbling thing I primarily notice it while at a steady cruise but in cooler weather it definitely starves out at WOT.

Forums like this rock, thanks guys!

 

[one2dmax]

The normal stage seven install has v-boost eliminators that replace the crossover valves. They are silver in color. The original valve system would be connected to both sides by bracketry that lets the cable pull the valves open with the servo motor.

It does sounds like it may be a bit lean and the needles you have should be adjustable so they could be changed just a bit by adding a washer or moving it one clip setting.

Sean

 

[gamorg02]

to get rid of the cruise stumble, i'd shim one washer and try it out. if it doesn't completely solve it move it an eclip

u said it stumbles at WOT in the cold. what RPM range?

 

[Daremo]

Sweet, will try that out. So the consensus appears to be that it is likely a tuning issue and not necassarily a sync issue? Just for my own info and since I wasn't able to find the answer can the carbs go out of sync when the v-boost is disconnected or since they are linked(as I understand it there are two carbs feeding a single cylinder every time it fires with the stage 7)is it not as big of an issue? Stil going to sync them mind you, just curious.

Thanks again for all the replies and suggestions!

 

[gamorg02]

well syncing never hurt anything! i like to do mine every 1k or so.

i'm pretty sure it doesn't help to synch them when they're linked, did u ever find out if vboost is just disconnected in the open stage or if the whole assembly has been removed?