make sure you are on #1 (even #6 works) plug wire. borrow another light. EDIT if you were on #2 it'd be 90 deg off (+your timing amt) so that (wrong plug wire) wouldn't be it. Are you useing a timing tape or a dialback? Might try a non dialback & 0.0632683" is (1) degree & 2&1/4" (2.246") is 35.5 degrees for an easy start. MORE EDIT after rereading I'm thinking what Flash said, vac leak or firing order. & it ran fine before & you had the heads done & the different cam (bigger or smaller just curious?), you did post specs but I ain't a cam guy.