1988 Marlin open bow with 4.3 Merc/2 bbl carb idle issue

[JBC118]

Hello, so I took my boat out for the first time this year. Ran great from the dock, idled around the lake, up on plane for a while. Ran it WOT for a bit, 4500 rpm, around 42 mph, trimmed up. Things were going well, very happy.
So we're idling around the lake at around 800 RPM and all of a sudden it seemed like the prop was hung up in the cabbage under the water. The RPM got all jittery and stalled out. No cabbage. BTW, engine temp was fine, around 165.
Took me a while to restart but when it did the engine acted like nothing happened. Prior to this the boat idled great, no stumbling, good power and idled perfectly.
Any thoughts?

 

[alldodge]

With a one time happening, it would be hard to determine, but would guess its probably fuel related. Have a look at the fuel filter and pour it into a clear container to see it anything is there but clean gas

 

[zellerj]

One theory: Bad gas. Suck some gas out of the bottom of the fuel tank and see if there is water in the gas. Running at 42 mph may have mixed up the gas tank contents so you sucked in bad gas. Junk and water settled to the bottom, below the pick up tube, while you were trying to get it restarted, so the fuel delivery system finally started delivering clean fuel again.

If it were an ignition issue, like the coil being bad, the engine would have turned off like turning the key. The fact that it stumbled leads me to believe it is a fuel issue.

There should be a fritted filter between the end of the gas line and the carb behind a large (7/8 inch nut I believe) nut. Check this out for crap from the gas.

 

[JBC118]

thanks for the quick reply, this system is a bit antiquated...no fuel/water separator and just that small filter on the carb fuel inlet...
The crud getting mixed in with the gas makes sense, i'll take a look at that..

The idea of draining/cleaning the tank seems a bit daunting. ..

 

[alldodge]

Yep being a 1988, no spin on filter, but does should have a filter as part of the fuel pump

http://www.mercruiserparts.com/bam/subassembly/31478/951/90