Miss Fire when warm

[jhelmick]

I hate to think of pulling M18 Kohler and replacing the module without someones expertise in this area, After mowing for about 30 minutes and the engine is nice and warm it starts miss firing and get worse the longer it goes. After cooling it is better, I can only assume the windings in the coil are breaking down........any ideas?

[J-Mech]

When was the last time you put spark plugs in it? Or adjusted the valves? Have you cleaned the carb bowl out, and fuel tank? Water in the fuel can cause a backfire..... Lets get some more info. What have you tried?

[dvogtvpe]

have you tried checking spark on each side when its acting up to verify it?

[jhelmick]

I have had fuel issues in the past and cleaned tank and carb completely, new fuel pump so I dont suspect a fuel issue, been running fine for a few months. The miss is like clockwork and just started a few weeks ago when its hot, 20-30 minutes it happens everytime. I tried different (not new) plugs when this happens and no change. I have pulled the plug wires when its running fair and the left wire will cause a major miss and the right wire will cause it to die. Have not had a chance to pull plug wires when really acting up. Still leaning toward ign coil (module)

[dvogtvpe]

if you pull the left and its a major miss you know the left is firing. pulling the right it dies which don't make sense since you know the left is firing.

[J-Mech]

Both of you know that the M18 is a magneto, wasted spark engine right?

It uses one mag, and fires both plugs at the same time. The only way for it not to fire on one cylinder is if a wire is bad, or a plug is bad. The wires are built into the mag and are not replaceable.

TRY NEW SPARK PLUGS!!! NOT USED!

Verify spark at both cylinders when its warm first. I doubt it is the mag, since it runs fine cold, and only appears to miss on one cylinder.

It sounds like the missing cylinder is the left one. Do a compression check on it with the motor hot. I think you will find that once warm, the compression on that cylinder will be lower than the right. Adjust the valves and see if that helps.

[dvogtvpe]

actually you can change the wire's if you know what you're doing and are carful how you do it. I've put those big yellow Accel wires on a couple Magnum twins before. looks cool. don't help with performance tho.

[J-Mech]

Originally Posted by dvogtvpe

actually you can change the wire's if you know what you're doing and are carful how you do it. I've put those big yellow Accel wires on a couple Magnum twins before. looks cool. don't help with performance tho.

If memory serves, the last one I saw, the wires were encased in silicone at the mag...... how did you manage to do that? Besides, I wouldn't recommend doing that. How did you reattach them so moisture would stay out? Did you change them looking for performance? Or to fix a misfire?

[dvogtvpe]

they are sealed with epoxy and there are allot of very good epoxy products out there. it was a perfectly good coil. just added the yellow wires for the cool factor. didn't expect any gains. I did cut one apart to replace a damaged wire once that got tore off somehow