Kohler CH980 mystery. Please help!

[BLES]

I'm losing my mind trying to help a neighbor....

CH980-0016

Starts and runs what appears to be fine. When put under load it labors, smokes black and won't power the large conveyor it's on. Removing the air filter (more air) appears to fix it, but I believe it's still under powered.

Carb has been checked/cleaned, and needle and float replaced, air cleaner assembly was changed to the cylindrical type (because a twin machine with that style works fine), all with no change. Air filter is NEW. No fuel in oil. It appears to be running on both cylinders. Doesn't seem to be ignition, plus I haven't seen an ignition problem produce smoke like this.

This machine worked well for a couple of years before this started.

Look forward to your ideas.

BLES

[38racing]

Might want to go beyond appears running on both cylinders. I test that by using an inline spark tester on both cylinders. They have exposed metal so its easy to use a jumper to ground out one cylinder at a time.

[Skywatcher]

Hi BLES

A very quick and effective way to tell if a twin cylinder engine is firing on both cylinders is with a second person. With the engine cold, have your helper wrap one hand round each exhaust header and start the engine. If he or she takes both hands off at the same time within 5 seconds of start-up, the engine is firing on both cylinders. If only one hand comes off and the other hand stays on for 10 seconds or more, that cylinder is dead.

Does this engine have a single barrel or double barrel carburetor? If the engine is firing on both and still running very rich under load, I would check to see that the main jet or jets are still in place. If main jet(s) still in place, you may have a plugged air bleed on the high speed circuit(s). Please let us know what you find,

Sky

[BLES]

It is running on both according to thermometer on each exhaust port. I find that to be more accurate than spark tester.
I will check carb again and report back.
BLES

[bgsengine]

It is running on both according to thermometer on each exhaust port. I find that to be more accurate than spark tester.
I will check carb again and report back.
BLES

Nothing more accurate than a power balance test with a tach & spark tester. RPM should drop the same for each side, if there's a very noticeable difference, then it proves one side is not producing full power as compared to the other side... temperature won't show that if both sides are firing.. only measuring actual RPM drop side to side will give a good representation of power output per cylinder.

[BLES]

Nothing more accurate than a power balance test with a tach & spark tester. RPM should drop the same for each side, if there's a very noticeable difference, then it proves one side is not producing full power as compared to the other side... temperature won't show that if both sides are firing.. only measuring actual RPM drop side to side will give a good representation of power output per cylinder.[/quote]

Good idea. I've never done a balance test, just checked to see if each side is firing. I started using temps as I often found engines firing (spark) on each side, but not REALLY firing (running), due to other issues. Do you have a spark tester that cuts power to one cylinder at a time? I just have a basic unit and use with a PET-304 or laser tach.

BLES

[bgsengine]

Do you have a spark tester that cuts power to one cylinder at a time? I just have a basic unit and use with a PET-304 or laser tach.

BLES

Don't even need a spark tester - using them just makes it easier to ground out each side without sticking holes in spark plug boots or over-stressing ignition coils by pulling boots off. Typically you'll want a PAIR of spark testers - one on each side. then all you need is a grounded test probe (ice pick and alligator clip jumpers works well.) As long as the probe has an insulated handle.. Then you'd just ground the probe, and touch probe to spark tester clip lead to kill that cylinder (and obviously will have to have tach hooked on the other side, for greatest accuracy) and measure RPM drop , then just swap around and repeat with other side.

[bobodu]

Plug condition should tell ya......

[BLES]

Don't even need a spark tester - using them just makes it easier to ground out each side without sticking holes in spark plug boots or over-stressing ignition coils by pulling boots off.

That's what I meant. I usually just pull off a wire for a second to see if it misses. Thought an inline tester that could be grounded would be easier and better.

Plugs show no visible difference.

Will report back when I find more.
BLES

Cleaned up quoting- AVB

[BLES]

Solved... sort of. Never could find the source of problem. I got a carb from another CH980 and swapped them and problem went away. Still no explanation why the other one ran so rich, but owner wants to leave well alone.
BLES