A4 Stops Running Intermittently/Lost Power

[RickMoser]

During my last two long trips (150 miles and 72 miles) without much wind, the original Atomic 4 in my 1969 Columbia 28 has stopped running a couple times after several hours while at speed as if the ignition had been turned off. I've also noticed that the engine has lost alot of power when in gear (it won't go past 2000 rpm) and makes a knocking noise when run at higher rpms in neutral. I think it could be one of the valves because when I checked the newest spark plugs after the failures, the fore plug was very dirty. I cleaned all of the plugs and the engine ran, albeit not more than 2000 rpms in gear. Upon returning to port on the last trip, I checked the dirty plug and it was dirty again after only three hours running. Everything else seems to be fine (i.e. cooling system, electrical, starter, oil pressure, fuel, etc.). I also recently put a few ounces of Marvel Mystery Oil in the gas tank, but noticed no change in performance.

A little history about the engine. When I bought the boat two years ago, the engine hadn't been serviced in at least 4 years. I serviced it myself (new plugs, alternator belt, oil change, fuel filter, etc) and have been servicing it myself on regular intervals.

Any suggestions about what the problem might be would be helpful. Do you think I'm correct in assuming it could be a stuck piston or bad valve? Could it be something simple like needing lead additive or octane booster in the fuel?

Thanks for any help you can offer.

[Jim Booth]

If it's only one plug that's dirty, it's probably not a fuel mixture problem. When you say dirty, do you mean black dry soot, or oily? If it's black dry soot, it's possible you have poor ignition to that plug. Did you replace the wires and distributor rotor too? Here's another thought, did you get the wires mixed up? I was surprised at how well the A4 runs even when you get a couple wires crossed .

If it's not ignition, a problem being isolated to one cylinder would indicate rings or valves to me. I would think sooty dry plugs would point to valves since that might be a way to mess up the mixture or get incomplete combustion. Oily would be rings. You could do a compression check too. Don's the expert on Marvel Mystery oil, but from what I've read here, it sounds like a few squirts in the bad cylinder would be a good cheap place to start.

Jim

[Don Moyer]

I think you have several problems manifesting at the same time.

Relating to the sudden shutdown, my guess would be that there is a loose connection somewhere within your primary ignition system that completely breaks down every now and then. If there are a few minutes after the shutdown when the engine will not start, this would be your opportunity to confirm that it is the ignition system that's at fault. Simply remove the coil lead from the center of the distributor while someone cranks the starter for a second or two while you hold the end of the lead close to the head to check for spark.

Regarding the power issue and the fouling of the first plug, you could indeed have a bad valve, broken valve spring, etc. However, before drawing any definite conclusions, I'd check the compression in that cylinder and/or perform a power check by pulling the plug lead off that plug. A broken valve spring could account for your noise. At higher RPM, a broken valve spring will result in a rather pronounced clattering noise that you might be hearing as a knocking sound.

Don

[RickMoser]

I'll do a compression check first and see what that tells me.

Thanks for pointing me in the right direction.

Sincerely,
Rick