Update on Cub 149 that died
 

I recently posted that my 149 was running beautifully and then it shot flames and died with no compression. I left if in the back lawn for the night and came back to it the next day. Wouldn't you know that it started right up and ran fine again. It runs fine for about a half hour or so then shoots flames out the exhaust and dies. Same result, No compression. The funny part about it is that i run Marvel Mystery Oil in my Kohlers and i usually dont have valve sticking issues. I have to admit, i have not done the De-carbon on this engine yet so that will be my next step. My wife is scared of this tractor now and wants me to go buy a box store tractor.....We all know that is not a option. What do you think?

Exhaust valve is starting to seize. Put 3 or 4 ozs of MMO in the oil and gas. It might smoke a little but that's ok.

Or better yet, remove the valve and clean it/hand lap as well as decarboning the combustion chamber.
Forget the "snake oil"

I'd bet it's running a little lean thanks to the ethanol in the gas.

I used to be anti-additives, but, I have changed my mind this year.

Gasoline quality is so variable from the vendors, MMO can be a real "fix" to a lot of problems.

If I could still buy AMOCO Ultimate Unleaded that was available in 1968, I would not need additives.

I am now +1 on Marvel Mystery Oil for single cylinder K Kohlers, I have seen 2 engines with sticky valves helped by adding MMO to the oil.

I believe that MMO can help when added to the gas also. I have not added MMO to the gas yet as I have not determined the correct amount.

I used to believe WD-40 was good for rust prevention until I found better products.

Just my opinion . - :bigthink:

2 oz. to 5 gallons is how I mix mine.

I'd be cautiously conservative on adding the MMO to the oil crankcase so as to not thin the oil too much.

Cub Cadet 123

It is not so much the alky in the fuel today, is it the absence of lead that causes the valve problems.
Tetraethyl lead was extensively used as an additive to gasoline; it served as an effective antiknock agent and prevented exhaust valve and seat wear.
It was eliminated because it fouled cat converters and health concerns.
Av gas still contains it.