Craftsman LT 12hp-quits after 10minutes..

[b_klarl]

Hi all,
I enjoy tinkering with my small machines but I have run out of ideas with this mower. I have a :
Craftsman LT 12 hp with electric start
Model # 917.254241
Approximate year of manufacture- 1987.
Engine; Tecumseh 12 H.P. model #142.376012

The original problem;
Carburetor was leaking gas and engine was backfiring.
In no particular order I ;
Drained fuel tank and added fresh gas.
Completely cleaned the carb , which was gummed up with deposits. Tested the float needle which is working fine now.
I replaced the flywheel key which was sheared
Adjusted the valves which were way out of adjustment.
Tried to clean vent hole in fuel cap by putting small wire in hole and by blowing it out with compressed air.
Installed new spark plug (type recommended in manual).
The mower now stars right up and runs great, for about 10 minutes and than dies. If I let it sit for some time it will start up again.
The fins around the cylinder head and the blower housing are clean- no amount of accumulated dirt or debris.
I am at my wits end! Any ideas or suggestions what else to check?
Thank you for your help and ideas,
Brian

 

[ILENGINE]

When the mower dies check and see if you still have spark at the plug. If no fire then replace the ignition module..

 

[b_klarl]

Thank you, will check that today!

 

[b_klarl]

Ilengine, thank you for your response. After a delay of a few days do to family obligations, I started my mower. Started right up. I let it idle for about five minutes and then mowed for about five minutes before it died. Then it died! Pushed into the garage, pulled the spark plug and grounded it to the engine body. It has spark. Please, any more ideas as what to check next?

 

[ILENGINE]

Since you still have spark, I think there could be still some type of fuel problem. Possibly a needle valve that is sticking shut sometimes, or maybe a vapor lock situation. When the mower dies is the carb really hot to the touch or more outside air temp.

 

[b_klarl]

I started the mower after letting it cool down for about 20 minutes. I let it sit and idle for a full 30 minutes to see if it was possible a vent problem in the gas cap. After idling for thirty minutes I started to mow in 5th (of 6) speeds. Stalled in about 5 minutes, although this time it restated right away. So I mowed again, this time in 2nd gear, very slow speed. Well, it lasted for about 6-8 minutes and died.
I felt the carb, it felt cool or at least air temperature, not hot. Is this info of any help to anyone?

 

[RussellTP]

Check the fuel cap with vent hole, clean the vent hole or get new one..

 

[Thegeek]

Check the fuel cap with vent hole, clean the vent hole or get new one..

I'm with this one. Just loosen the gas cap and run it. I have the same issue with my mower, but can稚 find a gas cap locally.

 

[Joe Austin]

Don't know if you have this fixed or not, but I would look at or replace the fuel line from the tank to the carburetor. Sounds like it is restricting the fuel flow (since you have checked the other items) Joe

 

[hrdman2luv]

I'm guessing the carb doesn't have a solenoid attached to it. If it does, then there's probably your problem. Mine did that, and I replaced it, and it worked fine.