Have a 36 vanguard with 189 hours. Motor runs great except for every now and then, seems to only do it in salt water. I can be driving WOT and all of a sudden I start losing rpms...if I back off on the throttle the problem seems to go away. I noticed this past weekend when the motor would loose rpms the fuel filter would be full to the top, when it runs good its only 1/2 full. Any idea what the problem could be?

Are you sure the plug wires aren't getting salt water intrusion & arcing out? You said it only does it in salt water...

My buddy's motor did that. It was brand new. Would do it when the motor got hot. Something with the carb, he just bought a take off from mb and never had that problem again

Touch the heat shield next time it does it(unless you have a prexsiting heart problem or pace maker)

I did put some silicone where the wire runs into the boot then taped the hell out of it with electrical tape. Did notice that when I grab a plug wire it gives me a pretty good shock. Is that normal? My next try to fix this was get new spark plug wires.

Check where the wire comes out if the cowling

Wires don't look like they are in bad condition, boat has been kept in a shop it's whole life.

Run it with the lights off, see if u can see an arc

i had the same issue with my motor a few years ago. All I did was get a can of a sealant for plug wires from a auto parts store sprayed the hell out of my wires an wraped them with wire-loom all the way to the coil an never had a issue with it doing that again

Just fixed the same problem on my motor. It would cut out at WOT, then act right when I let off. It would've taken me forever to figure out why if I hadn't been running in the dark. I happened to look back and see the spark jumping across the #2 boot when it would act up.

The terminal on the arcing plug wire was rusty as hell. I scrubbed the new terminal and the bare wire down with Noalox, put it back in the boot, doped the wire end of the boot with some Dow 111, and slid a big piece of heat shrink over the whole thing. Once I shrunk the tubing down as far as it would go, put more Dow 111 between the tubing and the wire, and then wrapped it all in rubber splicing tape. A little more 111 between the boot and the insulator, then I should be okay unless I sink it.