4.75 hp B&S lawnmower revs then sputters


Old 11-12-05, 08:21 AM
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4.75 hp B&S lawnmower revs then sputters

My 4.75 hp B&S lawmower engine would run normally for about 5 minutes, then sputter and then quit. I replaced the carburetor diaphragm (which appeared damaged) and that solved the problem for about 2 weeks. The problem I'm having now is that the engine runs normally for about 5 seconds after starting and the goes through fast cycles of revving up for a few seconds and then sputtering for a few seconds and then revving again and sputtering again and on and on. I took off the air filter and noticed that the smaller one of the two springs between the governer and the carburetor had broken off. Thinking I had a quick fix, I replaced it with an identical spring exactly according to the specifications. But, this failed to solve the problem. Watching the carburetor as the engine revs and sputters I can see the intake valve opening and closing and the governor flapping back and forth. How can I make the engine run smoothly?
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Old 11-12-05, 08:57 AM
puey61's Avatar
Join Date: Apr 2004
Location: Upstate New York
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You need to clean the carburetor not merely replace the diaphragm. Pay special attention to the pick-up tube, it likely has debris covering the screen or jet.
Old 11-12-05, 09:55 AM
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When I replaced the diaphragm I gave the entire carburetor and gas tank a thorough cleaning.
Old 11-12-05, 09:29 PM
v8driver's Avatar
Join Date: Sep 2005
Posts: 767
did you soak the carb? you made absolutely sure to clean the tube? the governor on it, should be a windvane governor, that is if you see a plastic flap connected to the carb. they pretty much for newer ones, use two springs( make sure they are not stretched out) one link, and a windvane. make sure the butterfly isn't sticking, and the windvane isn't as well. you didn't fold the new diaphragm?

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