how much work has been done to the heads sure the push rods are right length ? are you holding any valves off the seat are the marks line up on the timing set right did you check the cam for events ? for it not wanting to advance sounds like the dist is ok you may have it jack up just to keep it running have seen this when the lash is way off go back thru your firing order look at you wires make sure there not cross like 5and 7