Craftsman lawn/garden TRACTOR

Hey All,

I have an old Craftsman lawn tractor that I bought at an auction a couple of years ago. I don't know how old it is, but it's in very good shape.

It has a 12 horsepower, overhead valve Tecumseh engine. It has run well for two years, but now, it appears to be overheating. It runs and cuts well for about 20 minutes, then it bogs down in tall grass. If I shift to a lower gear it runs fine, but eventually I have to go down to first gear to keep going.

Yesterday, I noticed that the gas in the gas tank is actually boiling when it gets to the point of bogging down.

I'm GUESSING that the intake valve is not seating properly, allowing compression to get back into the carburetor/gas tank causing the engine to starve for fuel.

What do you think?

Tom in TN

I would check under the fan shroud for any cooling air blockage from grass clippings and dirt. Hal
PS: If it has a main jet adjustment s/rew you probably need to open that as the engine may be starving for gas.

You probably have a very simple problem and it is called it needs to be cleaned. Grease and oil and dust cake up in and around engine parts and that stuff needs to be cleaned off of them once in a while. Pull the engine cover and blow/clean out the cooling fins etc and maybe even use something like the spray brake cleaner on it and I'll almost bet that it will run cooler and work just fine. Oh by the way I just picked up one like that and also found that the oil had gas in it and once I replaced the float and changed the oil it runs good or should I say it did I don't know now since I sold it the other day to a guy who needed a lawn mower

Agree with others that air flow restriction likely. Whatever you do after cleaning change the oil, it has been overheated, broken down and will likely cause you bigger problems if left in there. Another Tom

First thing to look for would be a big mouse nest under the engine shroud. Next check all the screens and the fan to make sure you are getting adequate air to the cooling fins.

If this Tecumseh engine has overhead valves it probably has nonadjustable electronic ignition and a nonadjustable carburetor.

On the off chance that I am wrong about that, a too-lean carburetor setting and late ignition timing (points set too close) will cause overheating.

We used to have a problem with mice building nests in small engine shrouds, very common.

Here's what I found when my tractor overheated. I think it was about 3 years. I pulled the head
so I could inside the fan shroud. I used air pressure after getting all this out. I don't keep cleaning rags in my mini-barn. Hal

If this is a late 70's single cylinder Tecumseh OHV, they had an overheating problem by design. Craftsman, Bolens, and probably other OEMs used this engine thinking that it would be a great new technology for small engines. But it was put into the marketplace before it was perfected. At that time I had gone to Tecumseh tec school and was a certified tec. We were seeing a lot of these engines failing from overheating at about 200 hours, and the factory would not stand behind the customer, the OEM, or the shop.

The problem.... The valve box sat on top of the aluminum head's cooling fins. Of course the rocker arms and push rods needed to be oiled, and so they were. But the heat of the head transferred up into the base of the steel valve box and the rubber O rings on the attachment (head) bolts could not take the heat and so cracked and failed. Now the oil was leaking down onto the head's cooling fins and forming hard crispy chunks that continued to grow from more oil escaping and baking until the cooling fins below the box were totally blocked. The heat would now warp the head, dropping the steel valve seats and destroying it.

In later series OHV engines, they found a better quality O ring that could stand the heat, and so the problem was solved. The cast iron cylinder and crankcase and lower end parts were plenty substansial, commonly giving an engine life of about 1500 hours.

Of course, mouse nests mean big trouble for these engines and all air cooled engines as well.

Paul in MN