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High rev after warm up

  • Thread starter Thread starter StinkiestBink
  • Start date Start date
S

StinkiestBink

Guest
Greetings all,
I have read many threads about similar issues, but still can't figure out my problem. The bike starts hard, (needs starting fluid on the first start) and when it does start, it seems fine for a while. It will then start up with no problem. After riding for a few minutes, the rpm's hit about 3-4K and stay there. If I engage the clutch to lower the rpm's it just revs back up again. I just fininshed cleaning the carbs and replacing the intake o-rings, (because i did find an airleak) but it still revs up once warmed. Also, i have set the air screws out 1 1/2 turns. It is a 1981 gs650. Any ideas?

Thanks
 
Higher "idle" once warmed up. That's the classic intake leak symptom.
I suspect you still have an intake leak somewhere.
 
I am at a loss as to where to look though. Do i just start spraying everything?

Thanks
 
No need to spray "everything", just the joints between the carbs and the boots, then the boots to the head. Also check to make sure your vacuum lines are not brittle and cracking.
 
But be aware that spraying doesn't always expose the leak. Many here have spray tested and found/heard nothing but later on do correct manifold or manifold o-ring replacement and the leak is gone. It IS possible to assemble the manifolds or their o-rings wrong and then you obviously still have a leak, even with new parts.
WD 40 or equivalent will make the rpm's rise a moment, water mist will make the rpm's drop a moment. I always use water mist.
But in your case, the classic intake leak symptom, I'd try tightening the manifold clamps after being sure the carbs are "popped in" correctly. If they are, I'd just take things apart because I'm sure the manifolds/or o-rings are leaking.
 
tight cable

tight cable

you may also have your throttle cable adjusted a little too tight. Noticed this when I did a handlebar change. If it's too tight, it will bind and result in high revs, including when you turn the wheel left or right.

Just loosen it up and adjust per specs. Might as well make sure it's lubricated while you're at it.
 
Adjusted the cable as recommended and adjusted the idle to 1200 rpm's while warm. This works alright, but it will not idle when cold. After about 5 minutes of riding it is fine. It backfires a little bit when cold as well. Also seems like there is a lack of power, (for a 650). Is there something that I should do with the mixture screws? They are 1 1/2 turns out now.

Thanks guys
 
Intake leak.
Adjusting the idle to correct rpm while warm will mean the idle will be too low after the motor cools. Then you'll have to adjust idle up just to get started again. Once warmed up, the idle will be too high until you manually lower it again...endless cycle of the classic intake leak. Trust me.
 
I've got a Shadow with the same simptoms. I just start it with the choke on and as soon as it starts, give it some gas. I then adjust the idle speed (which is a lot easier to reach than on a GS) until it runs at about 1500. Kill the choke after a minute or so. Then crank the idle speed down as it warms up. Easier done on a V-twin than an inline four.
 
Well boys, i am at a loss. I have sprayed the crap out of the whole intake area, with no change in rpm. I agree with the intake problem, but i have no idea as to where to look. Maybe i should start from scratch? The one thing that i did not do was to put grease on the o-rings because i have always heard that oil rots rubber. Not sure if the grease would help in sealing them thoough.
 
I posted this in tips last year but I'll toss it in here too...

I never use WD40 or anything like that for leak testing, it may work but its also going to soak your boots with oils and solvents and attract grime in hard to clean places. If it somehow caught on fire you'd have coated lots of things with sticky, flammable goo too.

I haven't tried water but I guess it would be OK in this place as long as you didn't go overboard, I'd rather hear the speed rise than fall though so what I do is use propane or MAPP gas.

Just take your plumbing type torch and put a foot or so of rubber hose on the end. Once you have the bike running so you can test it you crack the valve on the torch open and use the hose as a probe around each place you want to check for leaks.

Its easy to pinpoint a specific location, leaves no mess, you can shut off the fuel and take away the gas at a moments notice and works great for car fuel injectors and throttle bodies too.

/\/\ac
 
I'm not saying grease can't rot rubber, but I've been lubing cars/trucks for many years now and that's putting grease into a joint that's sealed by rubber. I've never seen any rubber boot or seal rot. Only damage is cracking/tearing/drying up from the outside elements.
I've also always applied some high temp bearing grease to all manifold o-rings and never experienced any rot. It's also very important to not over-torque the o-rings.
If your manifold clamps are tight and the correct manifolds are being used and they've been installed on correct order (if that applies), then one or more manifolds or o-rings are leaking somewhere.
 
had the same problem with my 82 1100 .im not sure if the petcocks are the same? if it is a vacuum petcock pull off the vacuum line ...plug the carb port...run it on prime,maybe that will do it.if so, some body tell me what to do ....i've been running it like that for a while.[-o<
 
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thinking it may be the diaphram in the petcock? run fine the way i have it
 
i tried hooking it up that way for a couple of days. the idle definitely went down a little, but the idle speed was still high after warm up. Basically, i am going to have to wait for a rainy weekend and tear the intakes all apart again.

Thanks to all that replied.
 
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