Just rebuilt??????????? Awful lot of oil/carbon fowling on top of those pistons!!!!!!!!!!!!!

looking at the pics---it appears that there is an sizable amount of inexperience work on this engine---

What hasn't been addressed is that on cylinders #1 and #7---the intake port is next to a water passage in the intake manifold---a poor gasket /sealing match between the manofold/head surface would/could cause the oil fouling present and also fill 1 & 7 with water from the water passage port