pto belt comes off cub cadet model 123 with 42" deck

[CubDieselFan]

Try this, clean your points with a old style fingernail file and then set them to 0.020. I cut grass for the neighborhood when I was a kid. I used a 102 and I would have to do this a couple of times a summer. I put a lot of hours on that Cub.

[knucklescraper]

I sanded the points with 320g sandpaper. The nail file was an excellent suggestion CubDeiselFan and I have one but it has a point on it which got in the way.

I checked the timing and it was the same after sanding. Almost perfect. The 'S' is slightly higher than centered in the viewing hole. But that's how it was before I had the stalling issue.

When I mowed the grass, same stalling issue after about 1/2 hour.

Perhaps it is the coil after all. The coil wasn't as hot this time as other times the tractor stalled (it was a cooler day). Maybe it is just getting worse.

It is quite consistent at about 1/2 hour for the first stall whatever is causing it.

[Billy-O]

Maybe it's not the coil.... Maybe you starved of gas because the gas cap may not be vented properly.

[Grandpa53]

Make sure you have good airflow across cylinder and head from flywheel fan. If you are mowing weedy areas the flywheel screen needs to be checked every few minutes and cleaned of weed debris if any has accumulated.

[knucklescraper]

Billy-O, the cap holes seem clear but I happen to have a spare cap so I'll try that on the next mow.

Grandpa53, I'll definitely keep an eye on that screen. Maybe there is some other issue with the flywheel itself.

Thanks for the suggestions. It will probably be about a week until I mow again.

[jbrewer]

I'm often wrong, but whenever there's a stalling problem, I like to think it's a fuel issue. You can test the cap by just leaving it a half turn loose. It doesn't take much to get air in there from the small amount of gas these engines consume.

When it finally shuts down, do you ever get a backfire as it's winding down? Does it cut out all at once or just start losing power, engine pitch changes sound, and then dies?

[darkminion_17]

Check the valve lash....spec numbers are on the tag.

[knucklescraper]

So, I mowed the lawn this evening, the entire lawn, continuously for 2 1/2 hours. The only thing I changed since the last mow where it stalled after 1/2 an hour or less was the gas tank cap.

The old spare gas tank cap I put on has a visibly larger hole than the original one. I did push a wire through the hole in the original cap from both sides but replaced it anyway.

Another thing: the tractor always surged when it idled. That is, the rpm increased - decreased - increased ... while it idled, with the original engine and the replacement engine I put in. I used the same gas tank and cap with both engines. After replacing the gas tank cap, the surging during idling is gone. The engine runs smoother.

I had the surging issue so long, I didn't stop to think it might be related to the stalling issue.

Seems like the gas tank cap swap solved both problems.

jbrewer and darkminion_17 I only saw your comments tonight after my successful mow. When the engine was about to stall, the power/engine rpm would drop, pitch change. I would disengage the pto, put the throttle to max, and head for the garage as fast as possible. The engine would stop firing within about 10 seconds or less.

I set the valve lash before I put this engine in about 36 operating hours ago.

Thank you everyone for your suggestions - I appreciated all of them, and Billy-O for first suggesting the gas tank cap. I'm so pleased the tractor is running normally again.

That's it for my major issues.

I have one minor issue left: an exhaust leak (or oil smoke) on the left side of the engine. It's hard to tell where its coming from but I think from the breather plate. I'll try putting in the new gasket I bought in the near future and see if that stops it. I've already tightened the coupling on the exhaust pipe. i don't think its coming from there.