Kohler K321 misses firing

[Eugen]

This engine was running fine after replacing the bent exhaust valve. Went to mow the lawn the other day and it started to run worse and worse. Seemed fine at low RPM, but as opening the throttle would clearly miss firing at times. Here's what the firing miss sounds like:

https://vimeo.com/843024319




Something interesting: I hooked an ignition light in between the spark plug and coil and it shows a fat strong light only when I hear the engine detonating properly. When the engine misses the light is weak to none.


By the time I shot this video above I have done the following:
* replaced the carb with the one from the 444 which runs great
* tried a few different spark plugs, spark plug wires, condenser, and ignition coils
* replaced the points with new ones, and adjusted

So nothing fixed the problem.

Fearing the worst I took the head off again. It show zero evidence of blow by the gasket. Valves seem to be fine. I checked the points closing with the multimeter, while turning the engine by hand. Basically if it shows 1 then the points are open, when it changes from 1 it shows continuity, meaning the points touch. What do you guys think?

https://vimeo.com/843545047





The valves don't seem to be stuck at all. I have not yet checked the valve clearance.

[myerslawnandgarden]

I know you have tried several condensers, but the symptoms are of a bad condenser or one that is hooked to the wrong side of the coil. Should be on the - side along with the wire from the breaker points.

Bob

[propane1]

My expensive 4 cents worth. Well the prices of things right.
Hehe, any way, condenser not grounded. Pin that opens and closes the points sticking

Noel

[Harry]

I concur with Bob, that pesky condenser can be the problem. I switched to transdensers and have not had a missing problem. Harry

[Eugen]

Thanks for the advice guys. I checked the condenser and the bolt that fastens it to the engine was not tight. Seemed to run a little better after tightening the bolt, but still not as good as before. This condenser was new and installed after the engine was rebuilt. Then I grabbed an old condenser and installed it in parallel with the current one. Again it runs better even but not perfect. It got too late and I gave up for now. Next I'll disconnect the "new" condenser, just leave the old one, and readjust the points gap.

[Harry]

I cut an old condenser apart once being curious what was inside and why would one go bad. Amazing all there was a small strip of copper insulated by some cardboard. Harry

[Eugen]

I cut an old condenser apart once being curious what was inside and why would one go bad. Amazing all there was a small strip of copper insulated by some cardboard. Harry

Right, it's just a capacitor.

[Harry]

I cut an old condenser apart once being curious what was inside and why would one go bad. Amazing all there was a small strip of copper insulated by some cardboard. Harry

Right, it's just a capacitor.

So it shorts out internally is why they go bad? Harry

[Eugen]

Right, it's just a capacitor.

So it shorts out internally is why they go bad? Harry

Capacitors can go bad for many reasons, depending on its type. This type used on our engines, if you say there's cardboard insulation, due to age the insulator could get less insulating, from humidity that makes it inside. Other types of capacitors have mineral oil or an electrolyte inside, which either dries up or deteriorates with age.

The role of the capacitor across any electrical contactor is to minimize arcing which is bad for the contacts.

[Eugen]

Fixed it once again. I decided to replace the cable that goes to the points. It was taped together with the cable going to the positive lead of the coil. When I separated them... guess what. They were reversed. So at some point I must've reversed them.

It runs good once again.


https://vimeo.com/844773131