Briggs & Stratton 4HP engine running rough - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
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post #1 of 5 (permalink) Old 08-08-2010, 03:47 PM Thread Starter
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Briggs & Stratton 4HP engine running rough

Engine (which is on a Murray mower) starts and runs, but smokes and runs very rough. I think the fuel mix is probably too rich because the engine runs perfectly just before running out of gas in the tank. I have changed spark plug, the gas cap vent is clear and the engine runs the same when the air cleaner is removed.

Could anyone offer any advice as to what the proble might be? There don't seem to be any adjustments on the carb. This mower is a few years old, but has not been used much. I don't know if it relates to the engine problem in any way, but it started doing this just after an oil change.

Engine codes are:
Model: 10A902
Type: 2291 B1
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post #2 of 5 (permalink) Old 08-08-2010, 08:07 PM
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Is the oil level proper? It should not effect the engine operation, anyway.

I am going to guess that it needs a new gasket/diaphragm under the carb. Pay close attention to how it come apart, and watch the location of the spring under the carb. Make sure it returns to the same location. That should resolve your problem. Good Luck, and please report back on your results. (You should be looking at less than $5.00, I would guess.)

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post #3 of 5 (permalink) Old 08-09-2010, 10:07 PM
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I would clean/rebuild the carb first. Then if that doesn't work I would check for air leaks.

Some Of My Lawn-Boys (and others)
1972 8229B (D-448)
1979 R7268 (F-100)(Restored)
1986 7035 (F) (Daily Mower)
1987 Lawn-Boy 7073 (F) (parts)
1997 Toro 20481
2007 6.5HP Craftsman 21" bagger/mulcher (B&S)
2009 Toro 20331 6.5 HP (B&S)
6 Other 4 cycle mowers in pieces

Other Equipment
1992 Bolens Suburban ST 160 hydro w/ 16 HP B&S Vanguard w/42 inch Mower Deck
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post #4 of 5 (permalink) Old 08-15-2010, 01:12 AM Thread Starter
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Finally got around to working on the engine today. I replaced the carb diaphram and gasket (about $4) and the engine is running great. Thanks for the help.
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post #5 of 5 (permalink) Old 08-15-2010, 08:18 AM
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That's great news! Glad you found the problem. Half of the satisfaction has to be from doing it yourself.

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