MASSIVE backfire issue; I have tried everything with no luck

[jake7022]

Lately I bought a generic 80cc 2 stroke kit for my bike, but have been suffering issues with backfiring when braking or slowing down. I have checked connections, tinkered with the fuel mix, I even opened the cylinder and cleaned carbon off the piston (it had been running rich for a while before that). Nothing has seemed to improve it, it backfires whether its running lean, rich or just right.
I don't know what to do now, maybe get a new cdi and a spark plug? After that I have no idea.

 

[wheelbender6]

Its running lean. Check for air leaks.

 

[jake7022]

Its running lean. Check for air leaks.

When I first realized this was a problem I pulled the plug and it was completely black. It isn't running lean, I'm sure of that. I have it running at the right ratio now, and the problem persists

 

[Venice Motor Bikes]

I concur with wheelbender6... back firing is a lean condition... The fact that it happens when slowing down is because when the carb is closed, the heavy vacuum just behind the closed carb is drawing in air from a leak somewhere!