12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes

laynerd

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  • / 12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes
12 HP Tecumseh snow blower engine runs bad when hot after about 5 to 10 minutes. It sometimes cuts off but will restart easily.
It runs better at times on a partial choke.

The non adjustable carburetor and gasket have been replaced, spark plug cleaned, fuel line replaced, gas tank cleaned and ignition coil, flywheel magnet sanded to remove all rust and removed fuel tank cap. The carburetor bowl is clean. Fresh gas has been installed.

I intend to replace the ignition coil but doubt it is the problem since it starts easily when hot or cold.

The engine has overhead valves. I am guessing that carbon under the exhaust valve could be the problem although it has sufficient power when running properly.

Does anyone have any ideas?????
 

bertsmobile1

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  • / 12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes
My idea is rather than guessing and replacng parts that are working quite well you buy a neon tube in line spark tester or a colortune.

Hit the instrument and watch what is happening.

If the sparks stop then the engine slows down & stops you have an ignition problem.

If it continues to spark while the engine is not firing you have a fuel problem.

If you fork out the extra for the colortune you can watch the color of the flame and see if it is running rich or lean.

After that you can rotate the engine and listen.
You can hear the inlet sucking in and exhaust blowing out.

If you want to spend a few more $ you can beg, borrow, buy make or otherwise acquire a leak down tester.
Std compression testing is little use on small engines as most have a decompression mechanism which causes the results to be substantially lower than reality.
 

laynerd

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  • / 12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes
Thanks for your response.

Please clarify:

1) Do you mean I should hit the tester with my hand gently???

2) Will the tester show a light if the engine is not running when there is a fuel problem?
 

bertsmobile1

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  • / 12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes
Thanks for your response.

Please clarify:

1) Do you mean I should hit the tester with my hand gently???

2) Will the tester show a light if the engine is not running when there is a fuel problem?

TYPO try FIT in place of HIT. Auto correct does some funny things.

When the magneto generates a spark the tester will flash orange ( If you have the neon tube type ) if the spark generated is strong enough to jump the gap in the plug.

I have been playing with motorcycles for 50 years and professionally small engine for the last 4
However the spark tester is the first tool I use when trying to diagnose any engine.
With a spark tester & can of starter fluid you can diagnose about 3/4 of all the engines that come in.

If you want help, do as you have been asked.
Never assume anything with an engine.
 

laynerd

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  • / 12 HP snow blower Tecumseh engine runs rough and cuts off after about 10 minutes
Thanks again

My experience with small engines is that ignition coils normally fail when hot and then will not allow the engine to restart until it cools again. In other words they usually do not fail causing the engine to slow or shut off and then allow an immediate restart of the engine. Sometimes a coil fails and will not provide a spark when initially trying to start an engine.

I plan to purchase the neon tester.
 
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