So reaching deeper into the problem I checked the flywheel key, removed and checked the muffler, pulled the cover and checked the gap on the tappets. All was as it should be. What I did next was to eliminate the ground wire to the mag. Low and behold it ran and even revved up. I mowed for about 15 minutes without any sputter or miss firing but it seemed to only be running at about 90 percent. I shut it off but had trouble starting it again. It would continue to run but it was a struggle to get it to rev without backfiring. At this point I can only figure that it must be the magneto. I can't understand how I could go from having the best mower ever to the worst nightmare with just a burp!
Kohler M12 won't go over an idle
- Thread starter peejo50
- Start date
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
Solid state electrical devices have a finite life and it sounds like your magneto has come to the end of it's life
Nope. He had strong spark pack on page 1. He has solid fuel flow and valves are in spec.
I can only count on one hand, the number of valves, that were in spec, on a used new to me mower engine. Think I have a couple spare fingers too. Have to trust your valve checking procedure.
Again something got missed.
Post up a video of it starting and running.
Exactly it. Though I had what appeared to be a good spark when I checked the plug, it was inconsistent when under a load causing the missing and back firing. It was odd that it would only run at idle until I cut the ground wire for the kill switch. Doing that increased the rpm's though running like crap. Put a new magneto on and I'm back in business.
Thanks for all the input, folks. Hope this helps anyone in the future with the same issue.
VegetiveSteam
Well-Known Member
- Joined
- Jun 1, 2022
- Threads
- 0
- Messages
- 368
Glad you got it figured out and thanks for coming back and letting us know.
That's exactly why we were asking asking about your testing method. I don't know if you were using a tester that is something like the pic below but if so you're far from the first person to get fooled by it. It doesn't take much energy to make it glow. They can prove no spark but they can't prove good spark. A spark plug held against the block is also not a good test and potentially dangerous. You may see some fire jump the spark plug gap but if it's weak fire it will get blown out like a candle in the wind once the plug is back in the engine and under compression.
Hopefully that Magnum runs many more years. Definitely one of the best engines ever made IMHO.
That's exactly why we were asking asking about your testing method. I don't know if you were using a tester that is something like the pic below but if so you're far from the first person to get fooled by it. It doesn't take much energy to make it glow. They can prove no spark but they can't prove good spark. A spark plug held against the block is also not a good test and potentially dangerous. You may see some fire jump the spark plug gap but if it's weak fire it will get blown out like a candle in the wind once the plug is back in the engine and under compression.
Hopefully that Magnum runs many more years. Definitely one of the best engines ever made IMHO.
Main reason why, you need to test ALL electrical circuits under load. As in a good ol' PET-4000.