High idle -- 1997 Bandit 1200

1997 Bandit 1200, 27k miles.  Just got the bike running after buying it in September 2012, it was not running at the time I bought it.


Pulled the carbs and cleaned 'em thoroughly.
Put the carbs back on, borrowed the battery from my '98 Bandit 600,
and the 1200 fired right up!  Good sign.

Noticed it was idling high -- backed out the idle adjustment screw, no change.  When I revved it up, the RPMs would jump to 6000rpm and hang there too long before falling back to 2000rpm.

Reminded my of my 2-stroke street bikes (Kaw triples) when they have an air leak into the cylinder, this 'high idle' symptom.

Shut it off.
- checked to see if I forgot to tighten the carb-engine intake clamps -- nope they're tight.
- checked the spark plugs -- plugs 1, 2, and 3 were finger (and I mean a very small weak person's finger) tight.
"Ah, an air leak maybe at the plug holes" -- pulled all 4 plugs, cleaned and tightened them sufficiently.


Start it up -- still idles high, at 2000rpm, seems a bit better when I rev i though, doesn't hang up at 6000rpm and stay there/slowly fall to 2k.


Any ideas?   I wish I knew the history of the bike but the seller has moved over the 4 years since I bought it.
He told me at the time I bought it "runs fine just needs a carb clean."

Air leak. Choke cable. Throttle cable. Carb balance. Timing advance. 
These are the best things that I can think of to be checking.  
Good luck and keep us updated.

Bosco15 wrote:Air leak. Choke cable. Throttle cable. Carb balance. Timing advance. 
These are the best things that I can think of to be checking.  
Good luck and keep us updated.

Does it still have the caps on the vacuum test ports? There should be one on 3 carbs and the fourth it is used for the fuel tap.

Re-Cycled wrote:

Bosco15 wrote:Air leak. Choke cable. Throttle cable. Carb balance. Timing advance. 
These are the best things that I can think of to be checking.  
Good luck and keep us updated.

Does it still have the caps on the vacuum test ports? There should be one on 3 carbs and the fourth it is used for the fuel tap.

I checked all three rubber caps that seal the carb sync nipples -- they're in good shape and tight.  The vacuum hose operating the fuel petcock diaphragm is also okay.

I just got back from tinkering with it.  I sprayed starter spray around the intake manifolds and front of the carbs.  The revs went up a little, but not enough to conclude there's an air leak.

Although I had *thought* there was some slack in the "pull" side of the 2 throttle cables, just for schitts-and-grins I loosened the "pull" throttle cable at the bracket on the carbs.

And when I slid the "pull" throttle cable out of the bracket -- the throttle mechanism *closed a little more*.


In my defense, due to space limitations around the mounted carbs, if you don't have a small adjustable mirror, which I'd wished I'd had when I was troubleshooting this problem but don't, it's hard to be 100% sure the throttle is closed all the way.

I thought "now why is it, since I have adjust the "pull" cable at the carb end to have maximum slack in the cable -- why is it *still* not allowing the throttle to close all the way?  Could there be another adjustment somewhere I haven't considered yet?"

BINGO.

There is another adjustment for cable slack located *at the throttle grip* where the cable connects up to the grip.

That adjustment was set for *maximum tight/minimum slack" of the "Pull" cable.

So I loosened the slack at that adjustment point and BAM no more high idle.

How is it at my age, 57, with 41 years tinkering with bikes I could have neglected checking that is a bit sad.

Then again,  I thought I'd adjusted the "pull" cable for full slack on the carb end -- maybe that's why the handlebar slack adjustment didn't come to mind.


Anyway,  the dang thing is rocking now - thanks for the suggestions.

Great result. Good to see persistence paid off. 
Take heed young un's. :P