Looks like I need some more help - high idle sporatically

I finished my carb rebuild - after setting the valve clearances. I put in new butterfly shaft seals, new idle mixture screw o-rings, set the idle mixture screws at 2 1/2 turns out on each carb. thoroughly cleaned the fuel enrichment passages in the bottom of the float bowls. put new o-rings on the fuel passages between the carbs. cleaned the plungers and needles - clunk test done plungers move extremely freely. I put new intake manifold gaskets in but didn't purchase, cut out my own from Intake manifold gasket material. bench synced the carbs. everything moves freely in and out of the bike - set the float levels to specifications (that was a pain but finally got all 4 floats set). Ok so here's my problem. I put the carbs on the bike, opened the choke, and it starts right up - choke works like it should - I keep turning the choke down as the bike warms up and finally with the choke completely off the bike is idling fine. Then if you blip the throttle the bike revs up but won't come back down - sticking at around 4000 rpm's but I can use the idle screw to bring the idle down, but then it continues to idle down too far and dies. Even if I don't blip the throttle, and wait for 10 or 15 seconds after I have the choke completely off, the RPM's will take off on it's own - going up to 4000 RPM's and staying but again, I can use the Idle screw to bring it back down. (of course after everything cools down I have to turn the idle screw to increase idle speed to get the bike to idle correctly again.)

Sounds goofy to me and I can't figure it out but maybe it makes perfect sense to one of you guys. It's almost like there's a vacuum leak that doesn't occur until the engine is warmed up or the RPM's start to go up (perhaps higher vaccum causing a leak to open that isn't there when the idle is lower?) - in which case I suspect my home made intake manifold gaskets - Anyway, let me know what you guys think. Any help is appreciated.

Dan

 

Did you apply a little sealer to those gaskets? I don't bead them, but I do spread a thin layer over the whole surface, both sides.

Tried spraying anything around them while it's idling high, see if it reacts yet?

Go back to my thread where you told me about the wiring, see if any of what I said sounds familiar...I had a similar issue, and it resolved itself last time apart, but I'm not sure why. Anyway, I talked about what I did on that last round of carb-off...

 

I went back and read your post but it seems like I have a bit of a different problem - My choke seems to be working as it should - bike starts easy regardless of whether its hot or cold - if it's cold, put the choke on and starts right up and I gradually have to decrease the amount of choke as the bike warms up as the rpm's keep building. if it's already warm, leave the choke off and it starts right up. I don't know much about these carbs either so I'm willing to look into whatever. I can certainly pull the carbs back off and look into the enrichment circuits again and make sure everything's clear.

I tried spraying a little carb cleaner right at the edge of the intake manifold boots - no response on any of the carbs - haven't tried the propane thing yet though.

 

P.s. I did apply some High Tack on the boot side of the gaskets so that they wouldn't move as I installed the carbs - but nothing on the motor side.

 

Can you see if any of the carb linkage is binding and holding one or the butterflies open? Also just push down on all the linkage to see if anything is sticking.
Check for vacuum leaks with propane.
If that is all good then you need to block the YICS passage and vacuum sync. Make sure you have a couple of box fans running on the engine so it does not get too hot.

MN

 

That's likely all it is; you're just out of sync. A bench sync is the starting point; now it's running vac sync time.

Be sure you don't have rock-hard vacuum spigot boots too.

 

Just for kicks, since you still got the aixbox boots off, stick your fingers in there and feel if one slide is raised more than the others when it runs away....

 

I'm pretty confident that the carb linkage isn't binding - I have tried pushing down on all the linkages after it starts to rev up with zero affect. Plus it seems if the linkage was binding, the idle screw wouldn't work when I tried to idle it down?

I'll definitely try the propane test tonight and let you know how that works.

I'll work on doing the sync tonight also - I have the YICS tool from Chacal already.

 

I hope you're right, and that's all it is - will get it synced tonight and report back.

 

I'll do that - that would be interesting if that is what's happening.

 

Yeah might give you some direction as to the nature of the problem.

When mine was revved up, all four were reacting equally.

I remember something....but not quite enough to be positive...seemed like on my XJ650 when I first had trouble with the intake gaskets leaking, I was fooling around trying different things and I'm pretty sure when I'd cover up the smaller openings in the carb throats, the ones on top that go to the diaphragms, when I'd cover the one for the cylinder that was sucking air the rpms would shoot WAY up, OR it didn't react and all the OTHERS made it jump up when you covered them...one way or the other, there was a difference in how the tract sucking air made the motor react when I did that....