Having just rebuilt my OMC 3.8 V6 finally got around to firing it up at the weekend. It was a dry test no water and no sterndrive & no engine water pump rotation - just ran it for a few seconds. Everything went reasonably well once I'd sorted out the timing but I noticed that out of the ends of the manifolds, where you 'd normally connect the water pipe, I could feel a pulsed pressure while the engine was running. My first thought were that the manifolds are perforated and took to to my machine shop to be tested (still awaiting results) but could it have been exhaust pressure from the opposite bank coming back through the water/exhaust mixing vents in the riser?
