Back in Aug. 2007 P51D had a problem with a 16 HP Kohler. His description of the symptoms is so perfect, I'm just going to paste it:

I have a 2003 John Deere LT 160 with a single cylinder 16HP Kohler. It was mowing fine on Saturday. On Sunday, when I started it, it backfired several times, finally started, and it now runs very poorly. With the throttle at full, it doesn't develop anywhere near full rpm, actually seems closer to idle rpm. And seems very loud at that. As I slowly close the throttle, RPMs actually pick up a little, but then decrease as throttle is closed further. If throttle closed to idle, engine will die. If throttle is advanced into choke range, engine bogs and dies. Any load on engine (e.g. engaging mower clutch) will pretty much kill it.

Fuel pump is delivering fuel. Pulled the plug, and it was dark brown, with a little carbon on it. I cleaned it up and gapped it to 0.040", per the book.

Any ideas?

His problem turned out to be a sheared flywheel key. I got the same exact symptoms with a 20-something year-old K321 (rebuilt 7, maybe 8, yrs ago- low hrs.), 'cept mine's 12v. ign, so flywheel position has nothing to do with timing.

It was a bit hard starting Thurs. morning - backfired a few times, fired but wouldn't catch etc., but it got going. It dug/plowed its way through 15" of snow from the shop to the house just fine, then started the thing P51D was saying. My driveway's pretty steep (too steep to plow uphill if there's more than just an inch or so), so there I am, blade up, idling up it at a mile or 2 an hour because if I give it any more it just goes into this loud, low-RPM-'n-getting-slower, funk. Stepping on the clutch don't help. Only bringing it back to idle (then catchin' it before it dies 'n bringing back into the midrange real slow) keeps it from eventually starting to detonate. (BTW, if you don't catch it 'n it dies, it starts right up like there's nothing wrong) There's a hint of black in the exh. When it starts this but nothing major. The plug was clean 'n light brown, but I changed it anyway 'n finished plowing.

It ran out of gas going back through the shop door, so I went to a different gas pump 'n bought it some new gas (that wasn't old gas I was using before, but kind of sounded like it mighta had something bad in it, so I took no chances). Next day I thought maybe some improvement - it ran OK at more throttle 'n when it started to bog I only needed to step on the clutch 'n it would recover but a half-hour or so into plowing - no change.

I had another K321 carb up at the house (wrong linkage for the tractor) which I bolted on without result. You can hear there's a problem even with no load - it just doesn't want to run with the throttle plate past about half open, yet it runs sweet below that (if you don't count it won't idle).

I'd started to think maybe I lost the ign lobe off the cam, but it had .020 more or less when I took the cover off. I filed the points clean, and could have got more than .020 if I'd wanted. Started it up - little or no change (too dark to go drivin' but it's still bogging at full throttle. With no load it'll come to full RPM, but it ain't happy 'bout it. The way it actually runs slower and slower while working harder and harder at it makes me think ignition's happening way early, yet this is right off a cold start, so I'm not thinking carbon's going to be glowing enough to cause pre-ign. Could I be wrong? And how's the point of ignition tied to throttle opening besides too low octane ? The family cars don't seem to be having any problem with the gas.

Where next? Can't get new points or a condenser 'til Mon. afternoon- I'll see if I got one lyin' around that I trust (anyone know how to test one? Unless it's a dead short, how can you tell if it's no good?) And where's these timing marks again? The manual's no help. I can't see an S or a T anywhere. I look through the half-moon shaped hole in the bearing plate by the starter 'n all I see goin' by is 23 285, 'n on the other side there's a 1/2" hole in the shroud with 2 little lines goin' by. Maybe Kohler didn't put timing marks on these flywheels because timing's not adjustable - it'd just be nice to know if it's right.

I'm rackin' my brains here. Closest I've seen an engine behave like this was a jumped timing chain 'n this engine don't have one. Any thoughts are appreciated.

Ric

Did you or did you not check the flywheel key?

Hi,
Key unlikely on an old K series. Check the points for pitting? Doubtful that that is the problem. Battery ignition? Suspect that the coil is breaking down or the condenser is headed south. Could try the condenser first as a failing one will give the exact symptoms you say.
Incidentally, that one with the sheared key was caused by not throttling down before shut-off.
Peace,
Clarke

Well, saying I was going to find a condenser 'n actually finding one was 2 different things. I guess the further we get from the 70s, the rarer these thing get. The pile of old parts on the end of the bench turned up everything from this Spring's tune-up on Massey except the condenser, and everything else has a mag, but I finally remembered a 20hp twin in an old Bolens. I haven't even started it in probably 2 years, but it has 12v. Ign.

KISS, key's too hard to get at unless you're sure 'n besides, the clutch bolts to the flywheel. The tractor ain't going to push 100 bladefuls of snow, then climb my driveway a dozen times and keep the battery charged if the flywheel ain't firmly attached. I appreciate you offering to help but, reading that old thread from last summer, I knew that wasn't going to be my problem. Thanks anyway.

Clarke, your best guess was right on the mark. It's still a bit off under heavy load but that old condenser pretty much solved the problem. It's still needs new points and condenser, but the pressure's off. I got everything done that needed done by 3:00, I can plow more snow if we get it, 'n I got time to shop around 'n not pay the $40 the local parts place wants for 'em.

Thanks for the help. In 40 yrs. no vehicle of mine has ever been in a repair shop (except for warranty, of course) 'n I've never had a condenser crater quite like that. It had me imagining all kinds of bad things. Just proves you're never too old to learn!

Thanks again 'n Happy New Year, Ric.

With the key, you don't have to pull the flywheel or anything. Just look at the alignment with enough parts off. You can generally see the cutout in the shaft and the cutout in the flywheel. See if they are lined up.

Hi,
Glad to help, but many an older electronic ignition will often "send" you to the carb as many times as you want to go there! And that condenser should not cost more than 5 or 6 dollars. I think "published" retail is under $4.
Glad it helped, but remember that a condenser is a DC block and an AC path, when the RPM goes up, so does the AC frequency and access to the path.
Peace,
Clarke