I'm trying to start a motor rebuilt 10 years ago. It will briefly run, then back fire through the carb. I have checked and rechecked the timing. I have it set to fire a little after TDC. The Motor is a 350, AFR heads, 11 to 1 comp. Holley 700 cfm with a performance cam. I'm using 91 octane gas, Stock point distributer. I'm beginning to pull my hair out! Help me out guys!