thermostat B&S 12S902


Old 03-08-11, 02:17 PM
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thermostat B&S 12S902

I have a b&s 12S902 engine on a b&s pressure washer. It was running fine them started to sputter and quit. I have cleaned the carb and replaced needle valve and seat. It ran good again and then the same thing. I see it has a thermostat connected to the choke valve and wondered if it could be the problem. Is there a way to check the thermostat? thanks
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Old 03-08-11, 03:21 PM
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When is the engine dying? Is it soon after starting or after it has run a while and gotten up to full temp or is it just dying randomly?

I have never seen a thermostat on a small engine.
Old 03-08-11, 04:50 PM
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I had never seen a thermostat on an air cooled small engine either, but here it is. #291. And since it is connected to the choke link,I would look into it further.

Parts and Diagrams for Briggs and Stratton 12S902-1368-B1
Old 03-08-11, 05:14 PM
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That looks like the same thing on the Kohler XT engines Chinese made, they call an "Auto choke". Not seen one not work, usually it is the carb, needle and or seat leaking and the kit is a new carb.

Haven't seen one with a briggs tag tho.....
Old 03-08-11, 07:18 PM
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I have seen these, and have seen them malfunction, holding the choke closed. To test, crank it up and wire the choke open to see if it runs right.
Old 03-09-11, 06:09 AM
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Thanks for replies. I tried holding choke open, no luck. put gas in plug still no luck. checked spark and it is good. decided to check compression. I have a screw in type compression testor. It showed 30psi. that does not sound good but I don't know what it should be. do you know what the compression should be. it is a 8.75 hp 12S902 engine. thanks
Old 03-09-11, 07:14 AM
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I usually do a leak down type compression check so the compression release does not come into play.

Make sure you have the carb. removed or wire the butterfies wide open. You are right, 30 psi sounds quite low. I assume you tested with the cylinder dry. Did you try testing compression after squirting some oil in the spark plug hole?

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