XR650 backfiring carb off boot..HELP!

Fairly new to working on bikes. Working on an XR650L that is starting to backfire so hard that the carb is blown right off the boot. Adjusted the valve clearance. Finding that the carb doesn't seem to fit tightly into the boots anyways. Any suggestions? What may be causing the backfiring or way to fix it?



There is a clamp that goes around that boot that holds the carburetor firmly in place.  If it's tightened down properly, you would need quite an explosion to get it to come loose.


You need to provide more information about the circumstances where you're getting the backfire.

  • Is the engine pulling a load at the time?
  • How wide is the throttle open when it does this?
  • Is the engine warm or cold at the time?

It's not normal behavior for an XR650L, but so far you haven't provided enough information for us to help you.

I`ve only seen one XR650L that would backfire,,it was at start up..........it was the CDI firing before TDC...



somethings goofy  the boot shouldn't see any substantial PSI

The clamp is definitely tight, but it just doesn't seem to fit right. Usually happens when decelerating at a stop light. Engine is usually warm.

seems like your  combustion cycle is making it's way back into the intake


but it runs fine otherwise ?

Edited by Zimman

What's the history on the bike?


Any resent work done on it?

How long have you owned it?

Has the carby been replaced?

Other than that, bike runs like a champ. After adjusting valve clearance, has much more power. Bike seems to be doing much better now. Thinking it just needs new boots because they just don't seem to fit well what-so-ever. 


Bike's getting old. Had itself quite a history. Thanks for the help guys!

I actually ran into a similar problem when I bought my XR650L from a guy that had it jetted for CO.  I rode it with plans of re-jetting it and from time to time it would backfire a bit on decel.  One time it backfired and just quit.  It would turn over, I had gas, petcock etc, but it just wouldn't start at all.  

I went to the forums and eventually found something referring to a lean carb leading to backfiring. That let me to more research where it was mentioned that the carb boot can get popped off under a hard backfire.  So, I went back to the bike, popped the covers, moved the carb more into the boot and it started right up.  Now after re-jetting it, I haven't had the backfire problem, until recently.  

I thought to check the carb/boot connection again and noticed it was loose and went to tighten the clamp.  I realized however, even with the clamp fully closed, the boot/carb connection was still pretty loose.  This will lead to extra air coming in and a lean condition (so is my theory).  

I bought a new hose clamp that will hopefully have enough clamp strength to get a good seal.  I've heard of some guys using starting fluid while it's running to spray around the intake boot to see if the revs kick up, if so, you've got a leak and extra air coming in.  I'm sure the others on this thread have valid points about the boot not experiencing that kind of force, so this is purely based on my experience and some deep internet diving.  

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