If you have that much initial timing i don't really think the timing is the problem. Have you been keeping fresh plugs in it as you go along tying to solve this problem????
I had a 750 demon on a customers car that was leaking fuel on the secondary side thru the pv cut out. I never got the problem solved and he sent the carb back to summit for a refund. He got a 650 demon now to try on it. I was in that carb 8/10 times and i never found the problem..
Try running the car and then pulling the carb while the engine is still warm and see if the mounting gasket is wet with fuel. and also sit the carb on the bench on some paper towels and see if it makes them wet.