Idle problem...

I think this is my last mechanical issue with the bike. When I let off the throttle, it hovers at about 2200 rpm for a few seconds then drops to 1100 rpm. I've checked everywhere I can think of for a vacuum leak with a propane torch and can't find any leaks. What is the next likely suspect?

Thanks,
Jim

 

Do you pass the cluck test? Carb Pistons could be hanging. What do your plugs look like? Running rich?

 

It passed the "clunk" test but I haven't checked the plugs yet, but now I will.

Thanks

 

I would also suggest checking the plugs.

I remember reading that a lean condition will cause a slow/erratic return to idle.

 

How many turns out are the idle jets on the carbs? When I had stock jets in the carbs on my 81 XJ650 maxim, I had the idle jets 3 turns out each.
The best way to set them is with a colortune. Good luck.
baz

 

Leaks at the Mating Surfaces where the Intake Manifold contacts the Cylinder Head are hard to detect with Propane or Starting Fluid.

They Leak in an INTERMITTENT Fashion. When Manifold Vacuum increases at higher RPM's ... the deteriorated O-Ring Seal lets Air in at higher revs and holds near Idle.

Increase the RPMs for a Test.
Shoot Starting Fluid at the Intake Manifolds.
If the Revs race as the Fluid is applied; the Manifold Seals are to blame.

I will not remove a Manifold to install a New O-ring.
The risk of breaking a Cheap Cap Screw off in the Head is to great.

Instead, I remove the Carbs and apply a uniform bead of Sealant all around the Manifold -to- Head Surface.

On the Outboard two Manifolds ... I spray the Manifold and Head clean to allow "Masking Tape" to be applied to where the Sealant will be applied.
Using Duct Tape and Sheers ... I Mask-off a "Line" that will allow me to remove the Tape before the Sealant cures and make the job L@@K decent!
Otherwise the Sealant just looks gobbed-on ... no matter with what precision you use to apply it.

Pulling-off the "Taped" line will give it a measure of respectability.

The temptation is to remove the Cap Screws and do it right.
That's when you are standing there holding the Dice.
The Odds are 8 -to- 1 ... against you!

 

Thanks for all the help, I've got some checking to do.