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Discussion Starter #1
I am working on my Dad's STX30 12hp with a yellow deck. The engine does not smoke, but it has almost no power. The Kohler manual says with a CV12.5 engine it is difficult to check the compression accurately because of the compression release.

I starts fine, and runs smooth. How would I go about finding out why it has a loss of power?
 

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Usually, the air filter is clogged or maybe something with the governor.
 

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Discussion Starter #3
Air filter is clean. I had thought about the governor, I'll look in the manual to try to figure out how it works. I seem to remember the smaller Briggs engines had a plastic flap.
 

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Briggs engines are a little bit of a PITA with the fuel system. The governor is most likely your problem since the air filter isn't.
 

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Discussion Starter #5
It looks like it is rings. I checked the compression, it was 60. I put oil in the spark hole hole, it went to 100.

Anyone know how hard it is to pull the engine?
 

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It may not be rings. It could be the head gasket. A cheap part to replace and pulling the head off isn't too bad a job.
 

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Discussion Starter #7
Sorry about the late reply. It turns out it was the throttle plate in the carb slipping on the shaft.

A friend of mine figured it out. He had seen it before. The new shaft I ordered was a different design, so I don't think it will happen again.
 
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