HELP needed.....Engine Idle races after bike warms up

[Firewalker]

As in the title.......I replaced the idle spring as it seemed like the adjuster was vibrating and self adjusting.  I like an independent throttle as much as the next guy......but this is not all that enjoyable.

The spring replacement did not fix the problem and I now have no clue what would cause this.  

The bike starts/runs fine and idles fine for about 5 minutes.  Then it will race to 4-5k rpm.  Unable to correct by snapping throttle or pushing it closed.  I thought it may have been staying partially open.

Called the MC shop and he suggested it may be an "air leak"  

Does this sound like a vaccuum leak/gasket bad......carbs need cleaning?

It is a 99 with around 9k miles on it.  

Any advise would be appreciated.  

Thanks in advance.

Scott

[finmac]

I have a similar problem with my 02. On my bike the choke control has 2 effective positions: engine quits, or engine barely idles. After about 5 min of barely idling, giving it throttle causes it to race, like a stuck throttle at around 4-5k rpm. Moving the choke slightly towards the full off position immediately brings the rpms back down to idle. To me this suggests a sticky choke, tho I'm no expert... I work around it, and as soon as it starts to race I know it's full warmed up!

Fin

[Riggsy]

I'm no expert on the GS (yet - Pick it up Saturday :mrgreen: ) but I've worked on hundreds of bikes in the last 20years:

The choke also lifts the throttle butterfly to raise the engine rpm a bit while its on.
Check the linkages are clean and free, could be binding on slightly.

Firewalker : Called the MC shop and he suggested it may be an "air leak"

Possibly,
When the bikes warm does it pop (backfire) on the overrun? If so an airleak (running lean) is likely. Check your plugs !
(I kinda like it when it does that - shits people behind you with flames licking thier front tyres )

[Chris_B]

My 99 does this to. It will idle nice and everything for the first 10 minutes of my ride and then when i stop at a light it wont drop below 3000rpm. Mine actually idles a little bit low, the stock idle is supposed to be 1200 (?). but when i turn the idle up any higher than 800 or so and give it throttle the engine races and wont calm down past 4000. It really is a problem. Im going to check the vaccuum hose coming off the left carb. Whats the mixture screw supposed to be at stock?

[Firewalker]

My 99 does this to. It will idle nice and everything for the first 10 minutes of my ride and then when i stop at a light it wont drop below 3000rpm. Mine actually idles a little bit low, the stock idle is supposed to be 1200 (?). but when i turn the idle up any higher than 800 or so and give it throttle the engine races and wont calm down past 4000. It really is a problem. Im going to check the vaccuum hose coming off the left carb. Whats the mixture screw supposed to be at stock?

This is EXACTLY what mine does.  It doesn't change if it's choked or not.  The choke works fine and I turn it off after warm up ...... it idles around 1k.  About 5 minutes later......like you say at a light or something....it will race around 4k rpms.  The only way to correct it is to let the idle screw out ........ but then when you kill the bike and go back to start it again after it has cooled.........it won't idle por caca!

[Jace009gs]

I would say 80% possibility of an air leak...Those rubber boots that atach the carbs to the inteak are probably dry-rotted from all the heat and weather elements...plus gas will deteriorate rubbe anyways...check them out see if they are cracked and what not...

ok other 19.99% probability is that the throttle cable is catching some where...Have you lubed it recently? is it set up right with the 10mm nut at the base of the carbs? A little *I MEAN A VERY LITTLE* slack in the cabel is good. Should be a little play in the grip

This is assuming the plugs are correct, and nothing is floating around inside the carb bowls that might be blocking up a jet......Also the little o-ring near the sliders is in place as well. Double check all of the above and report back....

[Jace009gs]

also you might need a colder plug....


edit* sry about the spelling it's 1:00A.M. and I have not life

[ratz]

a couple of problems may be the o-rings in your float assemble, as well as your float needle being cracked, or dented. This allows a small amount of gas to seep by, and feed the engine.
I also found that part of the choke plunger stop, was slightly unseated, and was causing my choke to not shut off completely. It was affecting one carb more then the other. I will take a picture of it when I get back from my vacation, and post it.

[AprilIan]

I bought a 95 and had the racing problem (not high hot idle). the bike would accelerate on it's own.   After cleaning and refreshing the carb it still did it.  I took it to guy who used to race GS's and he said the the problem turned out to be combination of a tight exhaust valve, misadjusted floats and misadjusted air bleed screws.  Bike no longer does it.

[The Buddha]

OK I cant believe I didn't see this thread ...
Y'all may have vacuum leak ... wd40 around the carbs when running ... see if idle goes up ... however ... air leak will misfire and pop and falter in addition to being high ... and it will be a bit more erratic than steady ...
So ... Y'all might need rejet ... lean as hell ... down low especially ... its jetted to be lean like ... like Hillary Duff ... (Thanks davipu for the Lindsay Lohan comment few weeks ago) You need to buff it up ... yea ... 40 pilots, 125 mains and a #4 under needle ...
Cool.
Srinath.

[Firewalker]

will try that srinath......I remember doing a similar trick when I used to mess around with chevy small blocks.  

BTW how much would you expect to pay for the rubber boots going to the carbs?

any links?

Thanks in advance.

Scott