Backfire when decelerating

[minipex]

what would cause an engine to pop when getting off the throttle?
i have a hemi slightly built. i took it out on a stretch of road and was doing 40mph at 3500-3700 rpm with an 80 tooth gear 15 inch tire. all the while not giving it full throttle, little scary with no helmet and shorts....haha
i knew this engine would go good, but never expected it to be this fast. i weigh 250lbs

 

[Moedog07]

It's a running a little lean? Do you have a muffler on it?

 

[minibike_mayhem]

Lean is mean and i kinda like how it sounds through a open header IMO either way Ive been running mine hard every day for over a year problem free

 

[lostinbaja]

Check for an exhaust leak or your exhaust may be too short.

 

[davidlamb78]

I would guess you have an open header, or maybe your exhaust is too short.

 

[minipex]

11 inch header with hollow muffler. the spark plug is still white. i was told it is too lean. thanks i will jet up