4.3 Merc RPM drop at WOT, then no start

[Chain_skipper]

Had my boat out on the lake this weekend and had an interesting experience. I was cruising at WOT and noticed a drop in RPM, then back up, this happened twice. Slowed down and pulled in and stopped in a cove, After sitting for a few minutes I couldn't get the engine to turn back over. Ended up needing a tow.

My first thought was water in the fuel, so I took a sample from the fuel line where it enters the carb. After letting it sit for a couple hours, no water had setteled out, not a drop. The engine internals were all rebuilt last fall, so my question is, is this a rebuild the carb situation, or should I be looking at something else? The fuel line and pump up to the carb are all functioning normal. Fuel pressure reg is set to 6 PSI.

As always any help is greatly appreciated.

Engine serial 0C665406. 4.3 V6, 2 Barrel MerCarb

 

[Rick Stephens]

When you say 'couldn't get the engine to turn back over' do you mean it wouldn't fire or it wouldn't spin?

If it just wouldn't start, then you got a fuel problem. Carb needs kitting, fuel pump, filter plugged, one of those. I think you have a mechanical pump, any sign of fuel in the sight tube? If you don't find a cruddy carburetor I'd be using a fuel pressure tester.

Another thought is that the lower shift cable kicked a sticky interrupt switch and you are getting no spark.

Rick

 

[Chain_skipper]

Yes, it would rotate, but not fire. It did once briefly. This engine should have a mechanical pump, but it has been replaced by an electric pump, previous owner told me the engine had been replaced at some point. I'll check the interrupt, I replace the control cable for the shift lever and thought I had it adjusted properly. From what I can see though, there is no restriction from the tank, to the carb.

 

[Rick Stephens]

Wonder if there is any fuel in the carburetor... Might pull the flash arrestor and have someone pump the throttle handle while you look for throttle pump jets squirting fuel in.

Electric fuel pumps require an oil pressure switch to power them while the engine is running and a primer lead off the starter solenoid to run the fuel pump while the engine is cranking. If the fuel is clean, and the filters aren't plugged up, you should also check that the pump is getting power from the appropriate sources.