Engine Running Problem


Old 06-12-02, 11:01 AM
Mark Whitcomb
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Lawn mower oscillating

I have a yard man 3.75 HP lawn mower which seemed to run well last year, but oscillates (revs up then slows down) when running this summer. I tried a new spark plug and cleaning the air filter, but neither has helped. The carburetor is all plastic and doesn't have any adjustments on it.

Does anyone have any suggestions.

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Old 06-12-02, 09:11 PM
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Hello: Mark

There are several possibilities that can cuase the problem you described. Most likely it's a fuel flow problem.

Check the fuel flow into the carb by disconnecting the fuel hose at the carb. Fuel should flow freely and continuously. If it does, the problem is the carb.

There is most likely some gummed up fuel ports in the carb. Cleaning and cleaning them will resolve the problem.

Read the manufacturers online web site for product information, problem possibilities, causes and solving methods, part locations, disassembly, reassembly methods, repair proceedures and instructions, pictorials and schematics, which may be available online.

Read the RECENT postings and replies offered and the ARCHIVES, within this forum, for other postings and replies on this topic.

Most likely this is not all of the potential problems. The other resident small engine service and repair professionals and moderators, may offer additional suggestions, advice & help.
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Old 06-12-02, 10:37 PM
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Location: USA
Posts: 16,818
Sounds like you have the Briggs & Stratton 3.75 classic. There is a diaphragm between the carb and the tank. Replace it, and clean the screen on the carb pickup tube while you have it off. That should take care of your problem.

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