I need help here, I took the heads off my 351 and had a valve job done, I also replaced the chain, upgraded to a mallory distributor, and rebuilt the holley carb. I did this all at once. Put every thing back together and there is severe backfire (flames) out the carb. I have messed with it all day and am at a dead end. I checked cranking vacuum with the coil unplugged and I get ZERO vacuum. There are no leaks. I put the engine at TDC and took off the #1 rockers and noticed that the valves moved up when I did this. Is it possible that the head shop milled the head enough that I need smaller pushrods? Or do I need to pull the timing cover and check that the new chain is on right?