Starboard engine stalling when warm

[pschauss]

I thought I had this problem sorted out last summer but it has surfaced again. After running for about fifteen minutes at 2800 rpm my starboard engine cuts out and won’t run above idle speed. Give it more throttle and it stalls.

Here is what I have done so far:

Last summer:
- Replace the coil and ignition module: no charge
- Replace the fuel pump: engine would not start sometimes.
- Replaced the line from fuel tan to filter.
- Installed an anti siphon valve at the tank.
- Swapped port and starboard fuel lines.
- Mechanic at the marina took off the carburetor and cleaned it: stalling problem went away but it still had an intermittent non starting problem.

This summer:
-Different mechanic installed a rebuilt carburetor. He found a pinhole leak in the line from the filter to the pump. Engine starts consistently. I had put about six and a half hours on it, driven the boat about six times before the problem reappeared.

Any ideas?

[scenarioL113]

Is this problem of not going above idle speed happen when under load (in gear) or will it happen only in neutral?

Is the problem possibly an electrical problem? Maybe in ignition system? Distributor itself???

My gut leans toward a fuel problem but you have been thru it so IDK.

Have you tried to swap the fuel lines to run the opposite engine?
Do you have separate pickup tubes in the tank for each engine?

[pschauss]

So far, I have only seen it under load. My mechanic wants me to check it with a spark tester the next time it happens so my plan is to run a test in the slip when I come back after the next incident.

Port and starboard engines have separate pickup tubes at the tank. I swapped fuel lines last last summer and it did not make any difference.

My starboard engine has a Mallory distributor with an electronic ignition insert. I replaced both the insert and the coil last summer and it did not solve the problem.

Given that the problem happens only when the engine is warm I would expect vapor lock but the fact that the engine restarts and idles properly would seem to rule that out.

[ktm_2000]

When I had I/Os I had an issue where after 30 min or so one engine's tach would start bouncing and the engine would run like crap and I could not get it above idle. I replaced cap, rotor, wire, coil, ignition module, etc and finally figured out that the position sensor inside the distributor was going bad and only showing improper test results when the engine got hot.