[tdangle]

Don't worry about the timing right now. Even though a bump in initial timing can help performance, it won't fix what you are having happen. I suspect that you are basically flooding the engine when you mash it full throttle. I'm thinking the secondaries are opening very quickly and the engine just can't handle it. Can you disable the secondaries from opening and then try it?

Also something to check: Is there any chance that when you floor it the choke is closing. I see that it is a manual choke and if you dont have it wired open or connected with a cable that the air flow could be pulling the choke plate closed, choking your engine.