500HP starts missing in rough water conditions only?
 

Help please
I have a 38 Fountain with carbureted 500HPs. If water conditions are flat both motors run fine through the full RPM range. When conditions get more interesting (3-4 ft chop) and the boat starts to get tossed around the Port motor starts missing, spitting and will eventually cuts out off if I persist with trying to stay on plane. If I wait one minute and restart the motors everything is fine until the 3-4 ft. chop is encountered again. Sometimes if I “baby it home” by not going over 3000 RPM the motor will behave. If I push up to 3200 RPM the problem starts again.
This is what I have tried so far:
1. Confirmed that fuel is good and water free
2. Changed water separator/filter
3. Replace ignition coil, cap and rotor
4. Removed and reconnected main wiring harness connector at engine.

Any suggestions???

just guesses... float level/overflow or a bad wire in the harness

I had almost an exact same problem on one of my 6.2s last year.It ended up being a bad harness.Run the boat at idle in the water or on a hose and wiggle every conector it was not the water it was the vibration that caused mine.Good luck

Next I was going to swap the carbs to see if problem follows the carb. I will definitely try the harness and connector wiggle test.
Thanks

Can't hurt I spent all weekend chasing a problem fixed it this morning.Keep going back to basics try not to get something in your head it could be anything but the motor does not care what kind of water you are in.But something does not like the vibration 3-4s cause.

can you see black smoke when this happens ? possible floats to high and flooding..but I doubt it...sound more like a loose/bad/corroded conection somewhere, that main harness connector still would be the 1st place I would look at closely

Don’t remember any black smoke but will check. Don’t think it’s dumping fuel because when motor stops if I try to restart it starts up like nothing ever happened. Not flooded or hard to start at all. Also the transom is clean as in no signs of running rich… Thanks!

SOUNDS SILLY BUT CHECK YOUR SAFETY LANYARDS. MY 312 WOULD SPUTTER AND SOMETIMES CUT OUT COMPLETLY IN ROUGH STUFF.WORN OUT LANYARD CLIP.:angry-smiley-038:

Interesting.

And check the wires behind the dash. There might be a few plugs similar to trailer light connectors that do get corroded over time. Squirt wd40 in all of the ones you find and make sure they stay together tight.