Engine revs to 4K when warm randomly

[Guest]

Hello first post here.
I recently purchased a 81 gs850 for 200 bucks... Craigslist find has a title and runs. Got the bike put together the previous owner cut the exhaust off and it now has four straight pipes ( currently making a 4-1) stock air box was destroyed when it was layed down so ape pods are installed. So far I have done jets shimmed the needles and got it driving ok. However when it's warm the bike will randomly idle at 4K rpms when this happens it's as if the throttle is stuck shut the bike off and restart it the idle stays at 4K. The bike will idle great when cold with no choke and has great low end power higher Rpms flames shoot out all four pipes. Any advice on the extremely high idle? Btw carbs are sealed to the head.

[Oldman99]

Welcome to the forums!
I would think a random vacuum leak. Get her running and spray around the carbs to see if it changes how it runs.

[JTGS850GL]

Could be sticking carbs or throttle cable. Does the idle drop if you snap the throttle open/closed?

[TxGSrider]

Does it do it when the handlers are turned? If the throttle cable is routed wrong or adjusted too tight they can "randomly" idle like that.
Also, if you're going to run pods you'll need to go up allot on the main jets.. and with a "cut off" exhaust, I have a feeling you'll be going even bigger. I'd "guess" 150 or 155 mains would be a good starting point. (this wont effect your idle issue)

[Steve]

You say the "carbs are sealed to the heads", but did you remove the intake boots and actually change the o-rings?

.

[steve murdoch]

Carb o-ring kit for your bike.

http://www.cycleorings.com/

Intake o-ring kit for your bike.

http://www.cycleorings.com/intake.html

[Chriskrueger89]

50 degree weather the bike started without choke and idled for about a min and I took off to the gas station about 2 miles away ran great lots of power shut the bike down ran in and out bike started and idled for about ten min while I had a smoke took off and turned after a block engine revved to 4K and stayed there even after shutting it down and restarting about 4 times. This happens every time it's ridden can I rings cause that?

[Nessism]

50 degree weather the bike started without choke and idled for about a min and I took off to the gas station about 2 miles away ran great lots of power shut the bike down ran in and out bike started and idled for about ten min while I had a smoke took off and turned after a block engine revved to 4K and stayed there even after shutting it down and restarting about 4 times. This happens every time it's ridden can I rings cause that?

As already mentioned in this thread, the intake boot O-rings are the most likely cause. That detail and more explained in the Newbie Mistakes thread as linked in my signature.

[steve murdoch]

It is not good to let your bike idle for 10 minutes. Too much heat.
If you are working on a carb synch then have a fan blowing on the engine.

IF the rev rise did not happen until after a sharp turn then maybe there is something wrong with the throttle cable routing as mentioned by TxGS.

[Chriskrueger89]

Update.
New orings from boots to head checked throttle cable and that's good removed carbs from bike and checked diaphragms and needles since that was the last thing I changed and they check out good. I think I may need to sync the carbs next but when the bike revved today after reassemble I shut it down and saw a spit come out around the throttle rod on right side inboard carb can this cause the issue or should I not be concerned about that?

[Spyder]

Sounds to me that your floats are too low. Not shutting fuel off when the bowls are full. DUMPING fuel into the engine. Check your oil, if it smells like gas I would tell you to check your floats, and float valves.

Did you do a full tear down and dip on these carbs? All new O-rings and seals? Did you check the float height?

[Chriskrueger89]

I did not do a full tear down I bought the bike after the guy wrecked it pulled the tops and bottoms of the carbs and they are spotless previous owner had slips from a local shop showing full rebuild on carbs.... may have been for another bike since he had 5 gs850s sitting there. How do you adjust float height?

[cowboyup3371]

Chris, go to http://members.dslextreme.com/users/bikecliff and download Nessism's Carb Rebuild Tutorial that tells you how to adjust the float height. Do this after properly cleaning them as there are passages you cannot see. Trying to say they are clean by the tops being spotless is just like saying there can't be anything blocking up the sink if it's clean on top (hair stuck in trap).