Briggs 12.5 overheat

animalmechanic

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I blew an 18hp I/C in my mower and replaced it with a 12.5 but put the carb from the 18hp on it because the original was all rusted. It starts easy runs and sounds great but i noticed the exhaust valve stem through where the muffler bolts on so hot it was glowing. I bought a muffler off of eBay and put it on figuring maybe a little back pressure would cool it down. Runs for 10 minutes and cuts out, engine hot as hell. After it cools down the engine starts right up. Oddly enough a buddy of mine has the same engine with the original carb and its doing the same thing. Any thoughts? Mower deck 38" with good spindles, its not struggling to cut.
 

Luffydog

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Need to check and see if the engine is dirty and full of grass,oil or something blocking the cooling fins. Any type of materials that may be under the engines cover only creates a big blanket of a heat shield that won't let hot air out and fresh cool in. Make sure the engine is clean to start. Also improper fuel mixture will cause this as well. You changed the carbs out you stated just might be the issue on this as well as dirt build up.
 

animalmechanic

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Agreed, engine is clean i always check for mouse nests. I removed the heat shield. I hate to drop $50 on a carb just to see if it works but thats where im at.
 

Luffydog

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Just might be the gaskets that are bad and not the carb itself. Air leaks will cause a over heat as well to much air and not enough fuel. Test for leaks around the gaskets to rule that. Cheap enough for those than a carb or might be an different issue altogether and just hasn't showed it's teeth completely at this time.
 
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