K341 with weak spark

[Matt G.]

Is the gap correct? New spark plugs are not always properly gapped at the factory.

[Cvans]

Trying a new plug is a great Idea. I have had brand new plugs that were bad.I even managed to get a brand new "bad" plug back in the same cylinder that I took a bad one out of. That had me scratching my head for a while.
Good luck!
Chris

[MFP8055]

The plot thickens as I continue to search for spark. After checking all the wiring again and jumping directly from the battery to the coil, I managed to get a good hot spark... for a few seconds. It was enough to get the engine to run a bit and confirmed that no major mechanical (compression) problem existed. As soon as it stalled I removed the plug and found no spark again. Each time I do this I ensure the plug is grounded.

So here it is in a nutshell:
-All wiring checks out as well as points and condenser.
-Coil passes resistance tests.
-Compression and timing are good.
-Spark is non-existent, intermittent, or very weak most of the time. On a few occasions it appears hot and normal, but only lasts a few second.

I called my neighbor over who worked at a lawn equipment dealership that sold green tractors. He said it was not uncommon to see a coil fail even though it checked out OK with an ohm meter. It happened a couple times a year at his shop. Armed with that knowledge, I'm out to find a new coil. I hate throwing parts at a problem, but it seems to be the only thing left to try. Has anybody else had/seen coil issues. I believe the one I have is the 1978 original part.

[Rhoderman]

Coils go bad, and often fail with heat. Or moisture, or age, or internal arcing...

Feel it when it fails. Is it pretty hot, or just warm? Warm is good.

Is the case of the coil and the clamp that holds it clean? Measure the voltage between the coil shell (scrape the paint a bit) and a good ground with the key on to look for a bad connection. In this case, 0V means all is good.

You need a coil that takes NO EXTERNAL RESISTOR. Otherwise, your coil will get very very hot like mine did. Previous owner got me on that one!

If you can find the Kohler coil get it.

[R Bedell]

The Spark Plug Wire has to be a metal (copper) core type of wire. I have had this wire break internally causing intermittent spark. Bought new copper core wire and installed it.....problem solved.

[eastonct124]

Anyone know if a resistance test will work on a coil? I'd assume that a good coil should have zero, or near zero resistance. My experience with coils, is they work, they just just stop.

[R Bedell]

Checking the resistance on a HV coil is a good starting point. While on the bench and with your VOM, all can be checked. You can tell you if the coil is shorted or open. NOW, install the coil and put it under load, and you can get something all together different.

You can check the amperage of the primary winding, but unless you specifically had a HV Test probe for the secondary winding, it is just the "SWAG " observation.

There are numerous aftermarket coils that "claim" to work. The only one I would have faith in, is the Bosch Coil as suggested by David Kirk of Kirk Engines
( http://www.kirkengines.com/ )

[MFP8055]

I've got the machine running again after changing the coil. Even though the component checked-out OK on the resistance measurements, it turned out to be bad. It was tough to diagnose because of the intermittent performance and good ohm meter readings, but in the end, it was the only thing left. I bought a new NAPA 905 (no external resistor) and it gave a hot purple spark. The plug was replaced too, just in case.

I don't like throwing parts at a problem, but since the primary circuit (12V) was confirmed to be good, the component that turns the 12V into a 5,000V spark had to be the answer. Thanks everyone for weighing in on this issue. Much was learned.

[thenrie]

That was a problem I used to see when I was working on old cars. I also encountered it once on an inboard-outboard boat with a GM 6-cyl 235 engine. The owner (Dad) had replaced the coil, but didn't know he needed either a no-external resistor coil, or he needed to install a 6v ignition resistor on the + side of the coil. Regular 12v coils actually need 6 volts. They will handle 12 volts for a while, but will eventually get weak then fizzle out. We found out his error about 1/2 mile from shore in the Sea of Cortez. He said he had replaced that darn thing twice and it keeps going out! That was when I explained to him about the resistor thing.

You can use a regular 12v coil, but you have to buy an ignition resistor (a couple bucks), which is simply a voltage drop resistor that drops the battery voltage to 6v at the + side of the coil. Much simpler to buy a no-external resistor coil, which apparently has the resistor built-in, but either way is no big deal.