Briggs & Stratton reduced RPM


Old 05-04-06, 07:42 AM
Thread Starter
Join Date: May 2006
Posts: 7
Arrow Briggs & Stratton reduced RPM

I have a Lawn Chief mower, with a B&S 3.75 HP engine with diaphragm carburetor. It starts when cold easy, but have to push the primer bulb 2.5 to 3 times more than recommended. When hot it always starts on the first pull. The problem is that it sounds good but appears to be operating at 1/2 to 3/4 speed. The governor seems to be working. The carb has no adjustments. I have not attempted to take the carb apart since there is little that can be done. Air filter is clean and all the carb attachment screws are tight. Any suggestions?
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Old 05-04-06, 03:00 PM
puey61's Avatar
Join Date: Apr 2004
Location: Upstate New York
Posts: 3,224
You didn't provide engine ID numbers but being a 3.75 horse Briggs you should have the "Classic" engine whereas the primer bulb is integral to the carburetor (as opposed to being mounted in the air cleaner housing). The extra primes needed could be the primer bulb itself not sealing well, the check valve being faulty, or, a restriction at the pick-up tube in the tank. The lower RPM's may be that the arm at the speed control bracket that the governor spring attaches to got bent inward. Perhaps you have shrubbery you mow under and you happened to make contact with the speed control and pushed the arm in, effectively loosening the tension on the gov spring. You can simply bend this arm back to position to give the proper RPM's required...3400+-.
Old 05-05-06, 06:53 AM
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Join Date: May 2006
Posts: 7
Thanks puey.
I had about reached the same solution. Believe that the arm needs a good adjusting.

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