Lawnmower runs hot


Old 06-23-03, 05:39 PM
abNORMal's Avatar
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Join Date: Nov 2000
Location: New Jersey USA
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Lawnmower runs hot

I have a 5.0 hp Briggs on a Murray lawnmower (Hey! Quit laughing!) that starts hard and runs hot. I took the carb apart and everything seems to be in order. I cleaned everthing I could see. I think it's getting strange air. The idle screw seems to have no effect. The only place it could be getting air seems to be between the carb and the mainforld. This junction has an o-ring rather than a gasket and it seems to be in good shape.

What else would make it run hot?

Where else could it be getting strange air?
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Old 06-23-03, 07:59 PM
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Hello abNORMal. Welcome to the Small Engine forum.

The O ring is used to replace the gasket. Some engines use them while others do not. The O ring also allows for flexibility during vibrations, etc. Perfectly normal part to use in that assembly.

We have to assume you suspect and air leak into the engine when you say "strange air?" Possible but not as likely as the carb being restricted.

A restricted carb will cause an engine to become difficult to start and run slighly hotter than usual. Be sure to use the correct spark plug.

Take a look at the spark plugs color. The plug firing tip should not be white. Slightly black, brown and or tan in color is fine.

Remove the starter housing cover and clear out any debris under the cover, along the entire air flow path and on the cyclinder head.

Most likely I haven't covered all of the potential possibilities. The other resident small engine service and repair professionals may offer additional suggestions, advice & help.

Check back on your question several times over the next few days for additional replies.

Small engine repair parts, manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops. They are listed in the phone book directory in every town.

Regards & Good Luck.
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Old 06-23-03, 10:35 PM
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Join Date: Feb 2003
Location: southern louisiana
Posts: 365
Reasons for an engine to run hot:

1...lean mixture ----- could be fixed by turning the needle screw counter-clockwise. An air leak somewhere could also cause this. Make sure all the bolts that hold the carb and manifold to the engine are tight. While the engine is running, you can spray penetrating oil around these mating surfaced and if the engine speeds up, you found an air leak.

2...trash stuck in the cooling fins ----- Make sure to clean these out ocassionaly.

3...Restriced muffler ----- If carbon has built up in the muffler or trash got stuck in it, it would hold a backpressure and restict exhaust heat from coming out. If you tilted the mower to clean it, then oil might have gotten into the muffler, thus restricting the exhaust.

4...Valves out of time ---- If the exhaust valve doesn't have the propper clearance, it will not open enough and that would keep some of the hot exhaust from being able to escape the engine like it should.
Old 06-24-03, 04:56 AM
abNORMal's Avatar
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Location: New Jersey USA
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Thanks guys.
Sharp Yes, I suspect air is getting past the carb because adjusting the idle mixture screw has no effect and the plug is an ashy-white color. I had the carb apart and cleaned out the jet and other holes with a fine wire. The bowl is filling and all seems well there.

mower17 I like that penetrating oil suggestion. I'll give it a shot. If I follow all your suggestions and don't find anything, I suppose it could be a valve problem.

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