[cannon]

My Honda 450 Forman backs fires when you are going down hill and let off the gas. Why?

 

[retro]

Possible exhaust leak either from a leaky copper gasket where the pipe bolts to the head, from the joint where the pipe mates with the muffler, or a rust hole somewhere on the muffler.

Other possible reasons include a lean condition in the carb or a leaky carb mounting boot (intake manifold), or closed up valve lash due to wear and poor/none maintenance.

 

[LedFTed]

what does the plug look like. it might give ya a hint of whats going on.

 

[mrbb]

another thing that can cause this, is a CDI starting to go bad
and I have noticed that a LOT of the atv's at my hunting camp, that run ethanol fuel will do this, and all the one's that run NON Ethanol fuel do NOT, even same models and yr atv's
so, IMO< ethanol fuel can cause this some times too!
and yes a air leak in system can cause things to back fire too
timing issue's too

 

[cannon]

Thanks for your alls help.