The cam could be bolted to the gear out of index (180 out). If they ran the engine before you got it there should be carbon in ALL the exhaust ports (did you check this when you got the engine). This is a strange problem you have
. Something will "rear it's ugly head" sooner or later.
__________________
1970 T1 W/MassIVe 2913cc RAT/?EFI? w/direct fire (very soon) and 915 trans
1962 SC 1776cc SP 944NA brakes, 993 wheels
VKG