i recently rebuilt my motor, installing new piston,and rings, and just got it back into my bike. Everything is hooked up, timing seems to be right on, but the bike wont start. She is getting spark and gas. The only thing i can think of is that the timing screwed up after installation because we had it perfect before we put it in the bike. The bike seems to have low compression, and backfires probaby 1 in every 10 kick when we try to get her going. What is the problem??