High idle issue

[Skinner]

1981 GS650GL, stock

I installed new carb boots and o-rings yesterday. I thought the old ones were pliable, and they are, but not when compared to the new ones! I also installed new clamps. The airbox boots are very pliable and are in good condition, as are the clamps, so no problems there.

I reinstalled everything, synced the carbs and used my new Morgan Colortune to adjust the mixture screws. 1 and 4 were pretty good, 2 and 3 were running rich. The bike now sounds great and idles very smoothly. However, this is where the problem lies. It's idling at around 1800 RPM and I cannot bring it down with the adjustment screw. I can adjust it to make it idle higher, but no matter how much I back it off the idle screw it still sits at 1800. Could this be a matter of fine tuning the mixture screws? I'm quite certain I don't have any vacuum leaks. The carb boots are new, the air box boots are in great shape and everything is nice and tight. When I blip the throttle the idle drops back down to around 1800. I would appreciate any suggestions.

Cheers!
K

[Shawn68z]

How many turns out is your mixture screw? To me it sounds like idle is set too lean. Does the bike hesitate when you accelerate?


Cheers,
Shawn.

[MK3Brent]

How many turns out is your mixture screw? To me it sounds like idle is set too lean. Does the bike hesitate when you accelerate?


Cheers,
Shawn.

I personally use a wideband O2 sensor, it really helps get this all sorted much faster.

Look for vacuum leaks, considering you just changed out the boots. Get some brake clean and spray a little around the joints.

[lrgguy]

How tight is your throttle cable ? And did you bench sync setting butterflys using a paperclip or needle ?

[nejeff]

Check the cable at the carb end. You have it adjusted to high by accident probably. Adjust the locking nut and give it some more cable so the idle can go back down

[Skinner]

How many turns out is your mixture screw? To me it sounds like idle is set too lean. Does the bike hesitate when you accelerate?


Cheers,
Shawn.

I started at 2.5 turns and went from there. I used the Colortune to adjust the mixture. The bike does not hesitate when I accelerate.

How tight is your throttle cable ? And did you bench sync setting butterflys using a paperclip or needle ?

Check the cable at the carb end. You have it adjusted to high by accident probably. Adjust the locking nut and give it some more cable so the idle can go back down

The carbs were bench synced when I rebuilt them a couple of months back. When I reinstalled them I also vacuum synced them. And I installed a new throttle cable, which as it turns out is too loose. I have too much slack when I twist the throttle before anything starts to move. I'll tighten it up a bit today, but will make sure it's adjusted properly.

Look for vacuum leaks, considering you just changed out the boots. Get some brake clean and spray a little around the joints.

I'm hoping it's not leaks because that's the whole reason I installed new boots! I'll check this as well.

[terrylee]

New carb boot O-rings? Vacum line blocked if not using gas tank? terrylee

[Skinner]

New carb boot O-rings? Vacum line blocked if not using gas tank? terrylee

Yes, new o-rings. And when I vac synced I had the tube plugged with a golf tee. This happened when I was out on a test ride last night. Went for about an hour, same problem the whole time.

[tom203]

Make sure "choke" is fully off at carbs. And that you can see/feel slack in throttle cable at carb end.

[Skinner]

Make sure "choke" is fully off at carbs. And that you can see/feel slack in throttle cable at carb end.

I just adjusted the throttle cable because I had too much slack after I installed it. It's now just right, with a slight bit of slack at the carbs. As for the choke - I'm just getting ready to check everything out again.

[OldVet66]

Dab a little dielectric grease in the groove for the boot O-rings to hold them in so one doesn't slip when you install the carburetors.

[Skinner]

And the winner is tom203! The choke wasn't closing completely because of an issue with the linkage. The plug on the end of the cable wasn't seated properly and therefore didn't rotate into it's proper position. This resulted in the choke being partially open and the resultant high idle. I attached it properly and rechecked my mixture screws. Everything seems good, but I won't know for sure until I take it for a test ride later today.

Thanks for all the replies!

K