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Hanging Idle Improves with Mixture Screw- Weird one

C

canuck1969

Forum Apprentice
Have a weird one. Finished restoring my 81 GS50 and did a start up. Starts and runs without an issue except for a hanging idle. Checked for vacuum leaks and nothing that I can fine. Idles perfectly fine when warm and no choke. Stable and does not rise or fall. When I give it some throttle the RPS will rise and hang. Does not come down unless I rev it a bit more or shut it off.

Check all the obvious things. No vacuum leaks, carbs were cleaned (mechanical and ultrasonic including all jets) and air box is attached and carbs have been sync'd. All stock setup including the exhaust.

Here is the weird thing. I set the bike up with the idle mixture screws 3 turns out. As a last resort I reduced the turns out and got it to rev perfectly at about 1.25 turns. Now, from what I have read stock is about 1 turn so not two worried but it is reacting ass backwards to what should be happening which makes me think there is something else going on. Screwing it in should lean it out the mixture and make my problem worse, not better....No????

When I rebuilt the carbs the screws were missing the washer and orings so those were replaced. They are not stock from what I can tell as even when they are screwed in all the way they are just flush with the top making it impossible for a stock cap to be placed on it.

I have this suspicion that the seal is not very good on the screws. When they are 3 turns out I can wiggle the screw and there is little to know resistance on turning them. I wonder if I am sucking air in through the screws. Will source some new screws just to be sure.

Anyone have an thoughts on what could be happening?
 
Did you replace the carb boot O-rings? Spraying junk on the carbs only finds gross leaks, not smaller ones. And if the carb boots are the originals I'd replace them outright because if they are not cracked now they likely will be soon.

And if you use the proper size pilot screw O-rings they will seal properly. No need for those aluminum caps.
 
Nessism said:
Did you replace the carb boot O-rings? Spraying junk on the carbs only finds gross leaks, not smaller ones. And if the carb boots are the originals I'd replace them outright because if they are not cracked now they likely will be soon.

And if you use the proper size pilot screw O-rings they will seal properly. No need for those aluminum caps.
Click to expand...

yup. New o rings on the carb boots. They are originals but there were no signs of and cracks. That being said one never really knows but a liberal spaying of carb cleaner did not show any issues.

I am pretty sure I used the right size o ring as there was none in it to compare but checked with one of my other bikes. Unless it is some special size (1mm x 3 mm I believe but not sure). May just order another set of screws just to be sure.
 
canuck1969 said:
Have a weird one. Finished restoring my 81 GS50 and did a start up. Starts and runs without an issue except for a hanging idle. Checked for vacuum leaks and nothing that I can fine. Idles perfectly fine when warm and no choke. Stable and does not rise or fall. When I give it some throttle the RPS will rise and hang. Does not come down unless I rev it a bit more or shut it off.

Check all the obvious things. No vacuum leaks, carbs were cleaned (mechanical and ultrasonic including all jets) and air box is attached and carbs have been sync'd. All stock setup including the exhaust.

Here is the weird thing. I set the bike up with the idle mixture screws 3 turns out. As a last resort I reduced the turns out and got it to rev perfectly at about 1.25 turns. Now, from what I have read stock is about 1 turn so not two worried but it is reacting ass backwards to what should be happening which makes me think there is something else going on. Screwing it in should lean it out the mixture and make my problem worse, not better....No????

When I rebuilt the carbs the screws were missing the washer and orings so those were replaced. They are not stock from what I can tell as even when they are screwed in all the way they are just flush with the top making it impossible for a stock cap to be placed on it.

I have this suspicion that the seal is not very good on the screws. When they are 3 turns out I can wiggle the screw and there is little to know resistance on turning them. I wonder if I am sucking air in through the screws. Will source some new screws just to be sure.

Anyone have an thoughts on what could be happening?
Click to expand...

There is a spring that goes in there also
 
She is all Done......

She is all Done......

Got her running fairly well and tuned and sync'd. Bike is all done and ready for spring.........

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canuck...Hanging idle resolved?? You need to be proud, it seems you've missed nothing, Exceptional looking old GS. What's the gauge on the tach?? Now "my" negatives, I don't like BLACK motorcycles, I think the weird tail section Suzuki put on those 650's are about the fuggliest tail sections ever put on a bike...Great job, Congrats!!!
 
Yes, VERY nice machine.

BUT, how did you resolve the hanging idle issue?
 
Put new carb boots on but not even sure that was the issue. Put some new washers and orings on the mixture screws and put some thread sealer on the threads. Also lowered the idle a bit. All that seemed to tame the beast.

The meter on the tach is a volt meter. Put them on all my builds and has saved me every time from being stranded on the break in rides. Some electric problems on these old bike just creep up on you.
 
Just beautiful! I have the same model, year and color and can only wish mine looked that good! Personally, I like the tail on the 650G a lot. MO better than the boxcar tail on some of the GS's. The coffin taillight on the 650G is a bit hard to look at though.
 
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