i'm at about 700ft. and i put on a T-4 procircuit slip on pipe, with air lid on, and a 142 main, i think a stock 43 pilot, and the needle is on the 5th slot, mixture screw is out 2 1/2 turns, it starts fine and i can notice a huge power increase on the low end, but when i let off the gas i get some pretty wicked backfire, i'm assuming i'm running a little rich, but not sure, i know its better to run a little rich than lean but if there is anyting i can do to get rid of that pop that would be great, any suggestions i would appreciate it

 

Wow, you are way lean...try 168-175 main, 45-48 pilot, 4 clip on needle. Leave the screw alone till you get everything else pretty close