I'm writing in this old thread hoping that someone will chime in. I yanked a 350 V8 Vortec engine out of a chevy truck and set it up in my boat. I replaced the head gaskets and lapped the valves, after which it started and idled nice (for a few seconds, running dry), but when I connected the cooling water, the two center cylinders on the right side filled with water. I then replaced the right side head, same procedure again, valves adjusted and ready to fire, but now it just backfires through the carb, I've triple checked the timing, wires, ect, but to no avail, fresh gas out of an external tank, fuel pump working, nothing happens other than the backfiring. Need a little help here