I built a chev 355 small block and currently it is running like crap. It broke in and ran fine and after I partially dismantled it to retorque the heads it has been running lousy ever since. Initially I was off on a tooth on the distributor and after I got that straightened out it ran but back fired through the carb when I hit the throttle. Currently I have the timing set with the distributor advance disconnected at 10 degrees BTDC. I have a comp comp cam 12-211-2 cam shaft in it (.47 & .47 and 270 degrees of rotation) from thier tech line they informed me that for that cam I should have 8-12 degrees of advance. The car starts runs idles but when you hit the trottle you can feel that it seems to be loading up and then backfiring. Yes I did get the proper curve put into the distributor and yes I did check the firing order. The carb is 600 vac secondary holley. Confused.

Not sure why you 'retorqued' the heads, but if it ran good before and doesn't now.... what did you remove and replace? There would be no reason the mess with the distributor or fuel system. So, I'm assuming you removed the rocker arms and exhaust manifolds. The exhaust manifolds would not cause this. So its down to valve adjustment. Oh, you said something about 'one tooth on the distributor'. My guess is to take the distributor out, set the valves, then with #1 at TDC on the compression stroke, replace the distributor. Make sure the wires are in the proper order on the cap.

I removed the distributor to retorque the back head bolts. Also the roockers and headers were removed to get at a few bolts. (this I know now is pointless when using new bolts). When I disconnected the vacuum advance to set the initial timing I did not plug the vacuum line. I was told by someone more knowledgable to me that the distributor will still pick up vacuum and the weights in the distributor will cause initial timing to advance so even though I am setting it at ten BTDC it is likely it is at 15-20 and when I put the line back on the carb the timing also jumps up 5 degrees. His solution was to plug the vacuum line from the distributor and to find a vacuun port on the carb that does not provide any vacuum advance at idle (there is 3 to choose from on this carb and I was told that the highest one on the carb would be the best one for this purpose). I am going to try again with the distributor line plugged before I do anything else. I know where you are going with the rockers and there is lots of compression and each pipe on the headers is hot so I don't believe I tightened one down to much to hold a valve open. Still looking for advice though. Pston

Is your TDC timing mark steady when you flash it at the balancer? If it's moving around a lot then you'd need to check ignition firing. If it's points type, check them. If magnetic trigger, make sure all is OK there as well. I had a very ragged running engine that was caused by the hall efect sensor wires being swapped in the distro. I would also triple-ckeck valve lash. All it takes is one or two that were lashed while not on the base circle to make trouble. How's compression? Is it even?