So I finally got the boat (1987 Sunsport, 351 w/ clip down distributor cap) running reliably after almost two years of steady work on it.
One problem remains though, When I get the motor up to 3200rpm and above, it randomly backfires and knocks, losing power. Sometimes not at all, sometimes up to once every 10 seconds. It seems to do it more with weight in the boat, and I could be imagining, but it also seems to happen when I hit big waves.
The boat rips and runs great besides this...
It did it before replacing or changing anything, but things that are new;
plugs (properly gapped, don't remember the spec.)
timing set to 6 degrees
carb was recently rebuilt
Anyone have any ideas on what's going on here? 90% of the time it runs great and it's hard to keep the boat in the driveway with the way the weather has been...but I'm sure this isn't too healthy. Thanks for any input