4.3 Penta (1999) Sputters

[fabieber]

After sitting for a couple days the engine starts and runs perfectly until powering up to plane. Then engine sputters like it has water in fuel but clears up completely after about 6 - 8 minutes running at 3200 rpms. The water separator filter has no discernable water in it. I pulled the distributor cap and while I found no moisture I did find a white powdery "corrosion" on each of the 6 rotor contact points and also a black carbon type residue on the tip of the rotor itself. I cleaned all of that thoroughly but improved nothing. I use nothing but non ethanol fuel ( use about 25 gallons every 2 weeks so fuel is not old) and the problem has started recently as the weather has gotten colder and humidity has increased - I live in the Vancouver, Washington area. Boat is moored full time. It is also a commuter boat so is operated at least 3 days a week and therefore sitting in the moorage anywhere from 3-4 days over long weekends.

Any ideas?

 

[dypcdiver]

Sounds like condensation, have you tried running at night and looking for sparks along the ignition leads? Try some WD40 at connections in the circuits, it displaces water/damp.

 

[fabieber]

Would the short sparks show up because they are following the moisture to an outside ground?
Regarding the WD40 - would I put it on the spark plug leads only or could it even be lightly sprayed inside the distributor cap?

 

[dypcdiver]

Spray it on all the electrical parts of the ignition system and yes inside the cap too but wipe the excess out with a paper towel.