1981 MC S&S Carb issues I think

[tex599]

Discussed this in an earlier thread, but decided to start a new one. 1981 S&S with the PCM 351. Boat will run fine for 10 minutes or so and then will stumble and die at higher RPM, 2400 or higher. Has to sit for a minute and will restart, runs fine at low speed under load. No issues at high RPM with no load. Thought it was the fuel pump and replaced it, still having issues. Could it be the carb, don't know when it was last rebuilt.

[1redTA]

could also be an ignition issue, do you have points? and how is the timing and the advance springs?

[tex599]

Yes, still have points, not sure how to check timing or points. Did open the distributor and everything looks normal. Any advice

[tex599]

Not sure where the advance spring is either?

[TRBenj]

Originally Posted by tex599

Boat will run fine for 10 minutes or so

[quote=tex599;835832]No issues at high RPM with no load.

Originally Posted by tex599

then will stumble and die at higher RPM, 2400 or higher.

Your post is very confusing, but I *think* I understand. Please correct me if Im wrong:

1. The boat will run fine under all throttle conditions for a short period of time (<10 min).

2. After running for a short period of time, it will stumble and die above 2400rpm.

Is that right?

I have seen similarly described issues caused by both fuel and ignition. When was the last time you did an ignition tuneup (cap/rotor/points/condensor)? Have you checked for blockages in the fuel system (antisiphon valve, carb inlet filter at the bowl, fuel water separator)?

[tex599]

TRBenj-you got it right. Last ignition tune up, unknown, I have only owned it for a year. has new looking wires, cap and the underside of the cap, rotor, etc. . . look ok. Fuel Water seperator is good, have not checked carb inlet filter yet. Not sure where the anti-siphon valve is?

[TRBenj]

The antisiphon valve is usually on the tank. The ones Ive seen are built into the fitting where the 3/8" fuel line attach.

The case that reminds me the most of your symptoms was solved with a new cap and rotor... and the old ones looked "ok". If you dont know how old they are, I would encourage you to replace them with new so you are sure theyre good. If they dont solve your issue, then you'll have a good backup set, if nothing else.

Trying to diagnose an engine in an unknown state of tune can be extremely frustrating.

[1redTA]

I learned that when trouble shooting engine problems to replace the cheapest things first, they're cheap for a reason

[markismm]

Might be a fuel delivery problems before the carb. Clogged up fuel uptake line inside the gas tank was my problem with my 84 S&S when this same thing began happening.

[markismm]

Again - my thought...

Originally Posted by markismm

Might be a fuel delivery problems before the carb. Clogged up fuel uptake line inside the gas tank was my problem with my 84 S&S when this same thing began happening.