Ok, long story short, the carb ran perfect for years.
Last season at random times it would stumble and die like it had water in the fuel.
This winter I drained the tanks, found no water. I replaced the fuel lines, the fuel filters, the tank selector switch and fuel pump. Leaving the carb as the issue.
This year it does the same thing. It is very hard to start hot and cold, when it does start there is lots of black smoke. It seems to be running very rich.
I took the float bowls and metering blocks off and cleaned them with spray carb cleaner. No change except now it surges at idle. To reduce, but not eliminate the surge I had to close the idle mixture screws all the way. At higher RPM's it runs great until the stumble occurs, always at part throttle. Full throttle is fine.
I want my reliable running boat back. Any ideas??
The carb is a Holley 750 VC on a Harman Marine 454.