Idle That Rises Gradually

Okay, here's the problem.

Start the bike, let it warm up well. Idles around 1100 rpm. Steady and constant. Bike reaches a reasonable temperature per the gauge, around 12 o'clock on the temperature gauge.

Go for a ride, oh say 45 minutes. By the time I return home the bike's idle has risen to around 1500 rpm. The bike's temperature is comparable to when I left. If I reach in to the carburator idle adjustment and dial it down back to the original 1100 rpm it sputters and struggles to idle.

Any obvious things that might cause this behavior?

 

Running worse when warm usually means your running too rich. Also, I wouldn't take your coolant being a certain temp, to mean the engine is at running temp. I always adjust my idle after a good 30 min ride to make sure i'm at normal engine temp.

Plugs looking ok? Black? White? Let us know!

 

Thanks,

I'll look at the plugs this weekend and report back...but just to clarify, it doesn't run worse when warm, unless I dial the idle down from 1500. The idle seems to rise "naturally" (not the right word I'm sure) on its own during the ride from 1100 to 1500 if I just do nothing.

 

I had that problem & found the rubber caps on the carb ports would soften when hot & suck some air, I put stronger clips on & cured it.

 

Running better hot means lean. Yours is running better hot because the idle rises.

You either have a(n) air leak(s) or your mixture is too lean.

 

You can't expect the engine to idle at normal operating temp, when it's not is all i'm saying. My bike will idle 600 rpm no choke cold, 900-1000 when half warm, but a perfect 1250 after a 30 min ride.

Is this not the norm with these engines?

Basically if you can't get it to idle at 1050 after you've gone for a decent ride, but it DOES idle 1050 when just starting, there's something a miss. (1050 is the rpm you should be idling at)

 

Pulled the plugs and took a look. Mildly sooty but nothing unusual. Insulator is a light tan color. Will start looking for air leaks tomorrow.