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1981 GS450T very high idle made worse

  • Thread starter Thread starter jeffgs
  • Start date Start date
J

jeffgs

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I had a very high idle condition so I took some steps to resolve it.

Cold start 1,300 rpm about
Hot up to 4,500 rpm and climbing.
If I hit the gas rpm's fall back but then climb back up.

Checked for vacuum leaks and found none. When the idle climbed I switched the petcock to prime and pulled the vacuum line and the idle fell perminently. The vacuum line smeeled strongly of gas, was wet so it was leaking. Found excessive gas in the air horn of the carb, both sides. So I replaced the petcock, the o-rings on the hangers, checked for cracks, installed new straps. Everything tight.

Now it is worse so I obviously exaserbated a problem. It idles up quicker and higher and pops out the pipes. I am going to put a rag over the carbs while running to see if I can unstick something in the carb with vacuum and then check those vacuum diaphrams on top of the carbs with compressed air.

Anything else before I just rip the carbs apart and rebuild?

Also do you pour gas into the float bowls when you re-install you carbs? It was a bear to get fuel in them.
 
Oh and the plugs had a white electrode with the rest of the plug black with a fuel smell. The oil had a strong odor of gas as well
 
"Also do you pour gas into the float bowls when you re-install you carbs? It was a bear to get fuel in them."

That is what PRIME is for on your petcock. it fills the floatbowls without the need of vacuum from the engine
 
"...... I am going to put a rag over the carbs while running to see if I can unstick something in the carb with vacuum and then check those vacuum diaphrams on top of the carbs with compressed air."

let's skip the compressed air stuff - those diaphragms are fragile. Still your problem sounds like air leak,so recheck .
Good bet is to follow the carb tutorial like this one ...

http://members.dslextreme.com/users/cbsaunders/gs/gs450_carb_cleaning_guide.pdf

change oil due to faulty petcock-hopefully you got new petcock and not a used one to eliminate it as problem.
 
Thank you for the turtorial, I was looking for that.

I do remember wondering if I put the carb hangers in the right location. I didn't know if it was critical but did note what each one looked like so I could put it back in the right spot. But upon reading a turtorial on the newbie thread regarding the 850GS carbs it states the hangers have positions marked on them from the factory and they need to go back in the right location.
 
The intake manifold boots on the 850 don't have a specific order, but they are marked for left (cylinders 1 and 2) and right (3,4). No idea if your 450 has left and right boots. If so, they will be stamped L and R.

You replaced the petcock, but did you verify that the vacuum port on the new one does not leak as well? Choke pushed in and working properly?
 
Eli not yet. It got dark by the time I got it back together and fired. Plus the header paint was burning off.

I am going to spend some time with it this weekend. I got upset because I was a driveability tech for Chevy so I know I missed the real problem and that burns me up. I didn't just guess, I spent some time. It feels though that I did fix something just not the main problem which is why I think it runs worse. At worst the ols petcock did leak externally and I really did want to get this thing fairly restored before commiting to riding it.
 
Has it run correctly in the past, or is this bike fairly new to you?

Another big culprit for running insanely rich is missing rubber plugs over the idle jets. If the petcock checks out as okay, the only other thing is can be is something overlooked in the carbs.
 
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