I learned that lesson the hard way. I was working on an Allis-Chalmers WD-45 and gave it a tune and rebuilt the carb at the same time. When I was done, it wouldn't start. I had 2 systems I had to check out instead of only 1 if I had done it in steps.

Anyway, in my opinion, not being there to check it out, it sounds like it could be timing.

-Tim
'51 Chevy 3104 w/'56 235, 848 Head, HEI Dizzy, Corvette Cam, Split Manifold and Dual Carter YF's