So A month ago I replace my head gaskets (first time I have done anything like that) and after putting at all back together, I can't get it to start. I don't think my valves are to tight. I set the timing all the way advanced and get exhaust backfire. when I go about 5deg towards retard, I get carb backfire (cool fire though, great way to get a haircut. maybe I'll start a business 'Cougar Crew Cuts, shorter hair in under 30 seconds', but I digress ). Does this sound like a leaky intake manifold? Or maybe something else.