"Sticky" Idle

[paulorv]

So I was doing some routine maintenance and after putting everything back together and taking her out for a ride I noticed that while at a stop the idle sometimes hangs around 3000-4000 RPM while in neutral (or in gear with clutch down). If I start easing off the clutch a bit it will drop down to normal and stay there, even when put back in neutral. Sometimes if I wait long enough in neutral it will drop down on its own. I have checked the throttle cable and it doesn't seem to be getting caught on anything, which makes me believe it's the carb.

Anyone have any ideas? Much appreciated.

[Steve]

The most likely cause of a hanging idle is a lean mixture.
One of the usual causes of a lean mixture is a bad o-ring between the intake boot and the engine.

How long have you had the bike?
How long have you had this problem?
How long since the carbs have been PROPERLY cleaned and had new o-rings installed?
What are your mixture screw settings?

While we are at it, how long since the valves have been adjusted?
Even though they won't necessarily cause a hanging idle, that job is often put off.

.

[tc.young]

+1 on what steve said, new o-rings for both the carb and carb boot as well as a clean. the norm mixture screw setting after rebuild is 2.5 turns. if it's an intake leak as i learned you have to spray contact cleaner on and around the carb boots and the boot from the airbox to the carb. that's about all the research i found on the internet that i used to diagnosis my issue.

[Nessism]

Spraying stuff in an attempt to find vacuum leaks is an unreliable method unless the leaks are extreme. Best to change the O-rings as part of normal maintenance and be done with it. Vacuum sync the carbs too. Can't diagnose problems on bikes until all the maintenance is up to date.

[Steve]

... the norm mixture screw setting after rebuild is 2.5 turns. ...

That may be a common setting, but I would not call it "normal".

The stock (EPA lean) setting is about 1 1/4 to 1 1/2 turns, but the bikes run poorly with that setting and take forever to 'warm up'. Some bikes run well with the screws about 2 turns, others will require 3 turns. Not just every bike is different, every carb is different, so you have to tune each carb, not just set them all the same. On my son's 650, three of the carbs are set to about 2.5 turns, the fourth one is out about 4 turns, but that's where it works best.

.

[tc.young]

That may be a common setting, but I would not call it "normal".

The stock (EPA lean) setting is about 1 1/4 to 1 1/2 turns, but the bikes run poorly with that setting and take forever to 'warm up'. Some bikes run well with the screws about 2 turns, others will require 3 turns. Not just every bike is different, every carb is different, so you have to tune each carb, not just set them all the same. On my son's 650, three of the carbs are set to about 2.5 turns, the fourth one is out about 4 turns, but that's where it works best.

.

that's interesting to know, shows how little i know about carbs. thanks for the info

[paulorv]

The most likely cause of a hanging idle is a lean mixture.
One of the usual causes of a lean mixture is a bad o-ring between the intake boot and the engine.

How long have you had the bike?
How long have you had this problem?
How long since the carbs have been PROPERLY cleaned and had new o-rings installed?
What are your mixture screw settings?

While we are at it, how long since the valves have been adjusted?
Even though they won't necessarily cause a hanging idle, that job is often put off.

.

I've had the bike for about 6 months. It was abandoned in my garage by a guy I was renting a room to, and he didn't take very good care of it at all. The first thing I noticed was what terrible condition the intake boots were in, and replaced them with brand new ones. I also did a pretty thorough inspection and overhauled the carb (dipped, new o-rings, rejetted for pods) and did a complete valve adjustment with new shims.

For the next few months it ran fine until I had some trouble with the starter, at which point I ended up taking some stuff off to service the starter. It was after putting everything back together that I noticed the hanging idle. I haven't thought about using contact cleaner around the boots, is it similar to using starter fluid? Maybe the boots are loose, so I'll have to try it.

Oh, and the mixture screws are at about the recommended 2 1/2 turns for jetted carbs. I have not done a proper carb sync as the testing equipment is somewhat pricey. Hoping I can find someone that will let me borrow theirs or get it on sale.

[tkent02]

Hoping I can find someone that will let me borrow theirs or get it on sale.

You can use mine, unless you live somewhere else.

[bellucci]

He lives in South Park too?
Curt

[Steve]

He lives in South Park too?
Curt

Nobody knows.

It's not in his profile.

.