Banshee backfiring after top end rebuild.

[DrewT]

I had just recently got my Banshee out of the shop after having stock bore Athena nikisill coated cylinders and pistons put in it, adjustable timing plate on the OEM stator, went from I believe 17 or 18 mm domes to 20s, clutch basket rebuilt, v-force 4 reads.

The shop had it for way too long and I rushed him to get it back to me after a year and 10 days he said he hadn't had a chance to tune in to carbs and I told him not to sweat it that my brother is a two-stroke savant. Problem is my brother is out of state working for the next 3 months. The bike will start first or second kick and idle flawlessly, but anything past a quarter throttle and it bogs and starts backfiring predominantly out of the left cylinder. I put brand new spark plugs in it kicked it over revved it three or four times shut it off pulled the plugs and the left plug was black and oily and wet. It's got 50 fur pilot jet, and 162 for the main Jets my needle is in the dead center. The timing has been Advanced plus four. Please any help on where to start and how to fix this I'm dying to ride my bike. If somebody can help me out I can take videos of it running or whatnot and I'm very mechanically inclined to follow instructions on what to do.