470 Cruiser problems.

[Walleye Express]

I have a 1978 Grady White with twin 470 cruisers in it. After they run for 30 to 45 minutes the Port engine starts to loose RPM and power. It stays running strong but only at 3000 rpm or lower. If continually stressed it will finally loose all power. It's still getting pleanty of fuel through the carb when this happens. They scoped it and it slowly looses it's spark to the point where it almost dissapears. If it was simply a short wouldn't it start acting up right away when cold or warm? Why does this happen only after that engine has been running a while? I got this info from my Marina guys who work on it for about 5 hours today and thats all they found out. Any help or suggestion would be appreciated. Capt. Dan.

 

[Walleye Express]

Re: 470 Cruiser problems.

Ttt

 

[wire2]

Re: 470 Cruiser problems.

I'd take a DC voltmeter with you on a cruise, when the power drops off, check for the same voltage to the + terminal of the coil of both engines. I expect one is dropping off due to some extra resistance somewhere. You can also test it with a jumper lead from battery + to the coil +. If the engine jumps to life, that's it.
If the voltage is ok, or a jumper doesn't affect it, the next check I'd make will be the - pulse from the points. Could be engine heat related causing something in the distributer to expand, or the condenser to stop working. A portable scope to watch the pulse would show it.