Stalling Universal M3-20

[John Squire]

Any thoughts on the following problem?My new (to me) 1990 M3-20 (on a Catalina 27) is tough to start (glow plugs always required), runs consistently at 1100-3000 RPM and runs rough, loses RPMs and stalls, (especially after running awhile), at anything lower than about 1000-1100 RPM. Mechanic adjusted idle stop and hauled to check barnacles, no help - I asked about valve adjustment/injector cleaning, but was rebuffed.There's soot on the transom, but doesn't seem to be abnormal exhaust (marina mechanic didn't think exhaust was notably off color either). Fuel has been treated with algae killer and "injector cleaner" stuff.What do I try next?

 

[Gordon Torresen]

Stalling diesel

Your symptoms are consistent with fuel that is too volatile. The treatmedn stuff that has been added could be your undoing. I would try an alternate fuel source using qualith diesel fuel. (I tout Amoco premier grade). Get a can of good fuel and connect a hose from your lift pump and stick it into the can. Run the engine long enough to purge the old fuel from the system. You will go through a lot of fuel in a short time because the return will still be going to your regular fuel tank. If this improves the operation, change your fuel. If not, we'll work on some more ideas. Let us know, either way.

 

[John Squire]

Will do

Thanks - I'll try new fuel and report results after the weekend.

 

[John Squire]

No joy - same problems

I tried running on a clean fuel can this weekend to no avail. I didn't leave the marina area or get the RPMs up very high, but the behavior didn't change - ran ok over 1200RPM, coughed, stalled, etc. below.Any ideas what to try next? I got a second "could be valve adjustment" from a Catalina owner - if I pull the valve cover, do I need to have a gasket in hand, or is Permatex OK?