Another stalling problem

[T-bird]

The short version; I bought a rebuilt A4 5 years ago installed it myself on my Catalina 30 and it ran well for 3+ years. This year or so it started to die randomly and would not start till it cooled. Lately the run times degraded untill the last 2 weeks it stops after 10 minutes. It starts on the first or second crank and runs well until it shuts down very suddenly, maybe 1 or 2 seconds of falling RPMs then nothing. No shudders or coughs its quite smooth. Heres what Ive done so far; tested the coil 3.4 ohms w/ no external resister (as written on the coil) I also ran my spare coil with the same outcome. I rebuilt the carb. thanks to MMI manual; no change. Thermostat barely hits 140 degrees and I can lay my hand on manifold for a sec. Plugs are hot but clean. Salt water flow is good on my fresh water system. I have electronic ignition, and spark at the plug even with hot engine. The elec. fuel pump was tested and felt relatively coolish. Today after my 10 minute run and shutdown, I jumped a wire from coil to starter terminal after about a hour of cooling. It started but ran for 30 sec before nada. No oil pressure switch. Ill check my raw water impeller, which I ran dry a time or two. Im no mechanic and this gremlin has stumped me at every turn.

[Peter]

T,

Have you checked your fuel tank vent? Try running engine with fuel filler cap off.

Do you have a fuel pressure gauge installed?

HTH

Peter

[Sam]

With the EI try a 4ohm rated [and tested maybe a little higher] coil with external resistor not needed. Your "dwell time" is longer w/EI requiring higher resistance. This was all worked out on the forum experts back in 2009/11. If you want, you could experiment with a cheap auto store coil and if you have consistent running get a good one from Moyer matched to your EI.

[Sam]

As mentioned and as I have learned a 0 - 15 psi fuel pressure gauge is a very good idea for diagnostics for everything prior to carb.

[T-bird]

Peter; Thanks for the reply. I have been running the pumps intake hose straight from a gas can with plenty of vent. And I dont have a fuel pressure gauge. I did run the pump into a jar to check for contamination and found none. It seemed to flow good. Thinking I screwed up the rebuild I pulled the carb and there was plenty of gas in the bowl. I just realized that the last 4 times I started the cold engine it ran for 10 to 14 minutes each time (by my watch). Can a fully opened thermostat cause problems? I dont know if that happens in that window at 1200 RPM. Just grasping at straws. Thanks

[capnward]

Sure does sound like a coil problem. When you tried the spare coil, was it new, or used? Did you test it? See https://youtu.be/IlmvMWf_1o8 to check your coil.

[ndutton]

Fuel related problem
I think a fuel pressure gauge will only confirm you have proper fuel delivery to the carb BUT that is an important determination before looking elsewhere. Where are you located? If local (to me) I could loan you a known good carburetor for testing purposes. A test run with it would confirm or debunk a carburetor issue.

Coil/ignition problem
The more you say the more it's sounding like a damaged coil problem to me. One parameter missing from your reports is the coil input voltage measured from the small coil + post to a solid block ground while the engine is running @1000RPM minimum.

[T-bird]

Sam; I actually have three coils but have not tested two. I did see spark when I cranked the hot engine with a plug grounded on a head bolt. I know that I cant read the spark strength but I was trying to follow the suggestions in that thread; at least the ones that were not over my head. I'll look into a fuel pressure gauge. Thanks for your help.

[T-bird]

It seems that the the coil is suspect, but could it be an electrical issue upstream from the coil? Full disclosure: I wired the boat much the way it was originally set up except for the engine which a pro did prior to installation. I extended wires and such all up to specs, but no dedicated battery, charging systems etc. I'm hoping Neds engine running coil test will help Should I isolate the engine for the test?

[JOHN COOKSON]

Originally Posted by T-bird

It seems that the the coil is suspect, but could it be an electrical issue upstream from the coil?

Yes.
Have a look at the wire that runs from the distributor to the coil. There is a pinch point where this wire exits the distributor. The insulation on the wire may be worn at this location. Also check the end connector on the wire to be sure it is electrically sound.

ex TRUE GRIT