High idle when warm (1982 GS450)

[mattocs]

When the bike starts, it will idle just over 1000 RPM. After it gets warm (riding a few minutes) the idle jumps to over 3000 RPM. At first I thought it was a sticking throttle cable, but it's not. I bought the bike two weeks ago. The previous owner only put less than 200 miles on it in the last two years. I've put 400 miles on it in 10 days. This problem just kinda came out of nowhere. Ran flawless until today. My thoughts are a dirty carb or sticking choke. I'm mechanically inclined, but have zero experiance with carburated motors.

Any suggestions or thoughts??

[omaharj]

search "intake gaskets" or wait for someone else to post. I'm thinking 90% of the time this problem is the rubber O-ring became brittle and leaks. I know a guy with a 450,nice bike! Good Luck!

[tkent02]

Have you turned the big idle speed adjustment screw down? Use the choke for a higher idle when cold, adjust the idle speed when the engine is hot with this screw.

If that's not it, you have an air leak most likely, perhaps at the O rings between the head and the intake boots.
Could be the choke is not closing all the way. Could be other things too, but in all likelihood it is something to do with carburetion. These bikes invariably get carb issues when they sit too much. Take them apart and clean them out inside. Easy stuff.

*disclaimer* I don't know Jack about a 450, don't even know if they have these O rings and intake boots.

[mattocs]

Thanks for the help. I have checked the idle screw thing, and it's fine. I found a source online for the intake orings. I'm going to take the carb off this weekend, clean it up, and order those orings.

[BassCliff]

Greetings and Salutations!!

Hi Mr. mattocs,

Yes, the first suspect in such a scenario is an air intake leak resulting in a high idle from the lean mixture when the engine warms up. Make sure the airbox is sealed tightly. You may need carb boots or intake O-rings. A lot of the more common questions/issues are addressed in the links below. I'm glad you found us. Now let me say "Hi"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Nessism]

Thanks for the help. I have checked the idle screw thing, and it's fine. I found a source online for the intake orings. I'm going to take the carb off this weekend, clean it up, and order those orings.

Cycleorings.com has the intake pipe O-rings and a set of carb O-rings you need. It's well worth the effort to clean the carbs properly and replace all those old/hard/brittle rubber o-rings with fresh.

[blakebird]

Yes, the first suspect in such a scenario is an air intake leak resulting in a high idle from the lean mixture when the engine warms up. Make sure the airbox is sealed tightly. You may need carb boots or intake O-rings.

First - apologies for the brief hijack, but it might be of some help.

This thread was a timely find. A couple of weeks ago I bought an '81 GS1000G, that had just had the top end of the motor gone thru (honed cylinders, new rings, valves lapped and new guides & seals). Quite a craigslist find for $995.





The only real issue with the bike, was an apparent rich condition (poor mileage, fuel smelling exhaust), and an idle that climbed to 2500 rpms when it got good and warm.
It fires immediately from cold with no choke, and the idle speed is normal until you've gone a few miles.

I began to dig thru the archives of wisdom here and and elsewhere, and started on my list of things to check. I started a thread on AdvRider.com's The Garage subforum, and a few knowledgable folks from here (bwringer most notably) pitched in with tips.

The bike is completely stock with the exception of a K&N filter element.
There was no apparent leak or bad clamp connection in the intake boots between the carbs and airbox, and the intake manifolds were replaced during the top end work.

I removed the airbox, and the filter - and saw that the foam seal between the element and airbox was in bad shape. Rotten foam, mashed flat...and chunks at each end were just missing, letting unfiltered air pass.



I'm hoping this is the culprit.... as I dug further into it and couldn't find anything obvious. I replaced the seal with self-adhesive foam weatherstripping, and it seals fine now.

I removed the carbs and checked the o-rings at the intakes - all good, and the screws were all tight and the seal looked good and even all the way around.

The PO had a local privateer shop do some carb work, so there was an unknown I needed to check out. He said they'd rejetted for altitude and synched the carbs. I've never needed to rejet a CV carb for my 6,000 ft altitude - though the richness had me wondering what they might have done.

Main jets were stock 115's, pilots were stock 40's, the needle stock, and the diaphragms looked like new.
The floats were the correct height (22.4mm), and the float needles and seats looked as good as new. The float bowl gaskets were pretty bad, and had a layer of Hylomar or some gasket goo keeping them from leaking...so I'm waiting for a new set from Z1.

The carbs checked out fine, and looked so new....I was running out of ideas.
Seeing this thread gave me hope that the airbox seal was the cause.

I went ahead and ordered a petcock rebuild kit just because the rubber parts are so old, and the amount of grief a crankcase full of fuel can cause. It doesn't leak now, but...

And before I take it far from home, I will likely do the Electrosport stator and regulator/rectifier. Cool bike though....my 41st since 1968.

[mattocs]

Good info. Thanks.

I'm cleaning my carbs on Saturday. I'll look at the orings and all that then. Thanks again.

[Addy Leung]

I had same issue to my GS1100-16V before that when it get hot and the rpm is go 3000rpm.
I found the carb boot to engine is crack. I replaced the 4 boots. but the probelm is still there.
finally, I tune my carb and synz it very well. All the 4 pointer move at same time and scale. the idle now can keep about 9-1000 rpm when it is cold, and about 1100rpm when it is warm up.

for sure, I did replace the RR and stator, Dyna S with dyna green coils and good spark plug cables and ignition relay mod. the engine is totally stock and never open for repair.

Hope it can give you some idea.

[blakebird]

Cycleorings.com has the intake pipe O-rings and a set of carb O-rings you need. It's well worth the effort to clean the carbs properly and replace all those old/hard/brittle rubber o-rings with fresh.

I ordered a set tonight....it's not going to be any easier to replace them than it is right now, with the carbs on the workbench.

I took the float needles and seats out. The seat o-rings look ok, but they are no spring chickens.

[mattocs]

I was messing around with the bike today. If I hit the kill switch when it's idling high, but turn it back to on before the bike shuts off, the idle will go back to normal (1000 - 1300 rpm). So if I come to a stop, kill the engine, flip the switch to on again so the bike keeps running, it idles fine until I get on the throttle. Its not a sticking throttle cable, but I did spray down where the throttle cable connects on the carbs with a good bit of WD40.

I also broke the head off the bolt on the idle adjust knob. I think it's the idle adjust thing. It's on the right side of the bike, connected to the rear of the engine. It had a nut then a knob and a spring on it. I have it tightened as far as it will go now. Which is how I broke the head off the little bolt that goes through that knob.

[mattocs]

I just realized I've been running the bike with the fuel petcock on "Pri" which I assumed was primary, not prime. Would this have any part in my problems? I'm going out to turn it to "on" and see if it helps.

[Nessism]

Did you replace the intake pipe boot O-rings yet?

[mattocs]

Did you replace the intake pipe boot O-rings yet?

Not yet. I'm going to order orings tonight. I'll replace them regaudless if I fix my idle problem. I sprayed the boots with WD40 to see if my idle changed. It didn't.

[BassCliff]

Hi,

I also broke the head off the bolt on the idle adjust knob. I think it's the idle adjust thing. It's on the right side of the bike, connected to the rear of the engine. It had a nut then a knob and a spring on it. I have it tightened as far as it will go now. Which is how I broke the head off the little bolt that goes through that knob.

That knob on the back of the motor sounds suspiciously like the CAM CHAIN TENSIONER. This is not to be trifled with while the motor is running. If it's been broken then you may have some serious problems.

Is this what it looks like?



Have you located a manual for your bike? I would highly recommend one.


Thank you for your indulgence,

BassCliff