According to Mikuni American Corporation...

Mikuni American Corp says:

"It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers."

To see all their carb tuning material go to:
http://www.mikuni.com/fs-tuning_guide.html
and
http://www.mikuni.com/fs-carburetor.html

A lot of great stuff, especially for those of us with XJ900's that have Mikuni carbs. But also lots of general info that's useful for any make of carb.

 

I could not find anything on the BS 34 mikuni carbs thats on my 82 400 maxim . , but they did have as you say great information.

 

Baz:

Hmmm...could this be why mine is doing the exact same thing? Never thought that it could be a "normal" thing. It's driving me crazy as I always think that popping at high revs when cruising was a problem. Will research this a bit. thanks for the links and info...greatly appreciated!

 

Thanks for the heads-up, as I have Mikuni's on my 1200 Venture and there is a very slight pop occasionally. I was going to tear the carbs down (just aquired the bike a month ago), but maybe now I won't.

 

I know this is super old, but I never considered the popping that would occur through an open exhaust when the throttle is closed from a higher point on the tach. This would explain some things revving it in the garage. So nicely synced/tuned/synced/tuned.... nail the throttle for showing off purposes throughout the neighborhood, and I think, "Why the hell does it pop??"

Now I know. Thank you. I know it's late... but thank you.