81 XJ650 Fast Idle

My Maxim has run flawlessly for 7000 miles in the 1.5 or so years I've had it. Now, it starts and runs fine, but after it warms up, the idle speed increases from about 1000 to more like 2000 rpm. What sort of thing might cause this? It just started this the last 2 times I rode.

 

Did I stump the whole board here? Or was this a really dumb question?

 

I'd check the plugs first and see if they show you anything.

To me it sounds like a vacum leak. After it warms up some expansion and leakage may be occurring causing a lean conditon. I'd start by checking the obvious: Carb boot clamps for tightness, that all the vacum port plugs are in place and have no cracks, petcock\vacum line is not leaking, float levels are correct. You may just need a good carb cleaning.

 

Sounds similar to the problem I had. Only in my case it wanted to idle at 5000 rpm once good and warm. Bench-sync of carbs and valve clearance adjustment has improved it a lot. I still have to do a real carb sync and colourtune.

 

^^Thanks guys.

 

Jeff, try running a bit of Seafoam through and see if that helps. If you want to stop by the store today (yes, I'm working Saturday :roll, you can have the other half of the can I used yesterday on my bike. I had a slight stumble off idle and I think the Seafoam helped with that, too. If it doesn't clear up, you're more than welcome to come on over and we can synch the carbs with my Manometer and Colortune it, too.

 

Thanks Don. I also plan to order new carb boots to replace the cracked ones on the manifold. I'm betting that may be a source of a vacuum leak. I just hope I can replace them without breaking those cap screws. Know any tricks for that? My income tax should be in the bank in a couple of weeks, and I'll order the new boots then.