Ignition system problem

[TADTOOMUCH]

Anyone have this problem?

Engine runs fine even at full rpms until it gets up to full running temp and then starts to miss and backfire and won't run over 2000 rpm. Shut down engine and let it cool down for five minutes and it is back to normal. Oil and engine temp are always within specs.
I think the issue is somewhere in ignition system.
New fuel filters, carbs, coil, dist cap and rotor, and new voltage regulator. Have not changed resistor ballast or ignition module yet

[Paul]

Vapor lock???

[Paul]

On second thought, I had the same thing happen to my boat about 6 years ago. It turned out to be an obstruction in the fuel system. The boat would get up on plane and cruise just fine for a little while then it would stumble and backfire and would not run over 1200 RPM. Occasionally it would simply die and I could'nt re-fire it for 10 min or so. On one occasion when it died, I spun off the water/fuel seperating filter and heard a vaccuum (sucking) sound as the seal parted and saw that the filter has only half full. This indicated an obtruction. I traced the problem back to the tank and found something sloshing around in the tank that would occasionally block the end of the pick up tube and restrict flow. When the engine would stop and the vaccuum dissipated, the obstruction would once again drop to the bottom of the tank and the boat would run fine again for a short while.

I have since removed this obstruction (large horse fly that got in thru the vent that had no screen ) and the boat now runs fine.

Hope This Helps,

[TADTOOMUCH]

Not a fuel problem. Both engines have new filters and run off the same tank and only the port engine has this problem which I am sure is ignition related but can't isolate the component that is causing the problem.

[davidsmith]

Had the same problemon one of my engines and it turned out to be a bad ignition coil.

[TADTOOMUCH]

Not the coil. Replaced the coil, distributor cap and rotor, along with voltage regulator.

[Dan Faith]

The backfireing seems to be a clue. When you replaced the distributor cap did it come with a gasket? It sound like moisture in the diestributor cap arcing when the engine get warm moisture condenses and it cross fires look inside the cap sometimes you can see evidence were it burns a line. If you have a spare cap next time it happens change it takes about 3 min. see if it doesn't correct the problem.

[TADTOOMUCH]

Not distributor. Switched to other engine and works fine. Put new one on with gasket still same problem.

[nowlings]

I had a similar issue on my trojan (1966 interceptor powered). I traced my issue to the ballast resistor. Actually it had to do with voltage drop between the ignition switch and wiring to the coil and ballast resistor. Check voltage with a meter after the resistor when engine is warm to determine if you have a strong enough spark. You may also want to look at degradation of the coil wire which can cause an issue as the engine temps increase.

Good Luck!

[TADTOOMUCH]

That sounds like a couple inexpensive things to try. I can swap coil wire with other engine and see if that is the culprit and then swap the resistor ballast after that. I might just buy another resistor. They are cheap. I'll check the voltages and see what's up.

Thanks for the ideas.

[nowlings]

One more thing, you can try as a temporary test, to bypass the ballast resistor completely by connecting the two wires together. This will eliminate the lowering of coil voltage to the engine. If you have a weaker spark to begin with, the ballast resistor lowers it further.
Good Luck!

[TADTOOMUCH]

Fixed the ignition problem. It was the voltage regulator and the resistor ballast. Not all resistors fail immediately. Mine was in a slow death that made the engine start to miss and loose power when it got warmed up which felt like a carb problem or fuel delivery problem at first.

Then the resistor failed completely and the engine would only run with the ignition switch in the start position.

The voltage regulator had heated up so much that it melted the epoxy sealant on the back and it dripped down over the resistor ballast.

Engine runs great now.

Total cost under $50.00 so I was quite happy it wasn't something worse.

[Jerry]

Glad to hear you got it fixed. Over the years, whenever I have had a boat with the external resistor on it I have purchased the 4 prong model. That way if it ever fails I already have the replacement right there... you just unplug the wires from the top and plug it in the bottom.(or vice versa)