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Ranwell1, Small Engine Technician
Category: Small Engine
Satisfied Customers: 10304
Experience:  I Own a Lawn Mower Sales and service business (37years). Have 2-cycle and 4-cycle certification.
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I have a Simplicity Sunstar with a 20 Hp Kohler engine. The

Resolved Question:

I have a Simplicity Sunstar with a 20 Hp Kohler engine. The tractor is probably 20 years old. It runs great most of the time. Every once in a while, like today, I mowed for about an hour and the engine just quits and won't start. If you let it cool down for an hour, it will start up and run for another hour then quit again. It seems to be vapor lock. The engine seems to be too hot. I cleaned the cooling fins, I just changed the oil and it is to the full mark. The air cleaner is clean. The spark plugs are probably 4 or 5 years old, so they need to be changed. Any ideas why the engine appears to run hot or is that normal? Any idea on why it stalls when hot and won't start?
Submitted: 8 years ago.
Category: Small Engine
Expert:  Ranwell1 replied 8 years ago.

Several possible issues.


If you are right and it is vapor lock, the causes are that the engine is heating up the fuel line. Check to make sure that the fuel lines are not close to any part of teh engine that could heat it up.



The engine could be getting too hot because the engine is running too lean. Over the years ther may have been dirt, gum and varnish build-up in the carburetor. This eill either plug up sem of the small passageways or at leas restrict them. It still may run, but would run lean causing it to run hot.


Make sure that you are running the engine at FULL spead. Running at less than full throttle can cause an engine to overheat.


You actually could have a coil or condenser(id so equipped) breaking down after it heats up. You may have to replace the coil, points & condenser (or electronic ign if so equipped)


Last but not least. The gasoline MUST NOT BE OVER 30 DAYS OLD. Old fuel will cause many problems.


Also, You must use good fuel of at least 89 octane. Gas has changed over the years so we need to use better fuel.


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