High idle after warm up.

[dburdick]

I have recently balanced the carbs and the bike runs fine except that, after riding for several miles, the engine revs to high between shifts, and the idle takes a long (several seconds!) time to return to normal idle speed when I come to a stop. I go of the bike yesterday while the idle was still running high, and pushed against the cable track on the right side carb pair, to make sure the throttle had returned to the idle position, which it had. But the idle remained high. So I now know for certain it isn't a stuck throttle, or throttle cable. Any Thoughts? I just Added a bottle of Sea foam to the tank yesterday, so I'll see what that does, as I was thinking maybe one or more needle valves might be sticking open after warm up for some reason.

[MiCarl]

There are several things that can cause the situation you have. Assuming the carburetors are properly synched your most likely cause is lean idle fuel mixture. This can be caused by air leaks into the intake, dirty idle circuits in the carburetors or mis-adjusted idle mixtures.

 

Another thing that can cause that is low compression on one or more cylinders. Not likely on an '08 unless its been abused or neglected.

[Marcarl]

I got a sneaky suspicion that the sync is off a little. Try it again, just for kicks.

[Condor]

Your sync is not right. Everything balances to carb#2 (left front). I have a sneaking hunch you have carb #4 sync screw dialed in too much and it's overriding the idle setting on #2 . That's what's causing all the problems.

[cowpuc]

Gotta totally agree with all the advice so far. Some things you didnt mention was how far out you found your sync, whether or not your scoot was doing this before you did the sync, the type and condition of the sync tool you used and - if gauges, what kind of vac readings you may have been seeing. Another area of interest IMHO would be making absolute sure your throttle cables have measurable slack in them - if they are even slightly tight what you describe is common. Another area of concern would be slide diaphram condition and possibly a sticky slide ESPECIALLY if the machine has sat for any length of time and not been run. If it doesn't come around on a re-sync (and I am with these guys - my money is on it will) I would check the above and double check the slide's for stickiness right in the bottom of their throw - always seems like that is where I have noticed the most common area for stickiness.. Hope this made sense? Its been said that I am kind of hard to follow and you may need some expert interpretation of what I am trying to say

 

Another possibility is you may have caused a vacuum leak - check around closely - look at the area where you hooked up your gauges,, vacuum leaks (hoses not connected right, crack in sync nipple) can also do exactly what we are talking..

[dburdick]

Gotta totally agree with all the advice so far. Some things you didnt mention was how far out you found your sync, whether or not your scoot was doing this before you did the sync, the type and condition of the sync tool you used and - if gauges, what kind of vac readings you may have been seeing. Another area of interest IMHO would be making absolute sure your throttle cables have measurable slack in them - if they are even slightly tight what you describe is common. Another area of concern would be slide diaphram condition and possibly a sticky slide ESPECIALLY if the machine has sat for any length of time and not been run. If it doesn't come around on a re-sync (and I am with these guys - my money is on it will) I would check the above and double check the slide's for stickiness right in the bottom of their throw - always seems like that is where I have noticed the most common area for stickiness.. Hope this made sense? Its been said that I am kind of hard to follow and you may need some expert interpretation of what I am trying to say

 

Another possibility is you may have caused a vacuum leak - check around closely - look at the area where you hooked up your gauges,, vacuum leaks (hoses not connected right, crack in sync nipple) can also do exactly what we are talking..

I can't say how long it sat before I got it. I'm betting the slides are sticking as the carbs warm up. The bike revs fine w

hile cool. The throttle cable has slack after warmup.

[dburdick]

I can't say how long it sat before I got it. I'm betting the slides are sticking as the carbs warm up. The bike revs fine w

hile cool. The throttle cable has slack after warmup.

Well, the bike has sat for a few days with Seafoam in it. Ill be taking it for a ride later today, and hopefully, the Seafoam will have worked it's magic and disolved any gunk in the carbs. I opened the drain on the carbs last week before adding Seafoam and a tank of Premium gas, hope this helps.

[dburdick]

Well, it must have been crud in the carbs, as it has been more than a week since I added Seafoam, and the idle is responding better today. It's in the low seventys here in South Carolina, so the wife and I are leaving for a ride in just a few minutes. Merry Christmas to all!