Engine BOOM

I've been having problems with my 12 HP B&S Flat Head 281707 when at full throttle It makes a boom sound like someone Is hitting a bass drum. Sometime It goes boom boom boom I don't know If that's misfiring or what but doesn't sound good does that mean It's running too lean or too rich. It runs good underload for a couple minutes then starts to make the boom sound until I lower the throttle then when I put It back It runs ok for another couple minutes. I've taken the carb apart and cleaned It up real good with carb cleaner. It starts as soon as I turn the key, I checked the spark plug and It's fine+fuel filter and has fresh gas. I cut my neighbors lawn front and back and It bogged a little but never stalled. Just makes the boom boom sound and my small push mower does the same thing which Is also a briggs.

Since both mowers are doing this I would try removing all the gas from the two mowers and your fuel can. Make sure the tanks and can is clean. Now go get some gas and start over.

possum said:

Since both mowers are doing this I would try removing all the gas from the two mowers and your fuel can. Make sure the tanks and can is clean. Now go get some gas and start over.

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Sounds like a good idea, certainly worth a try.

Walt Conner

checking for engine miss:
try holding your hand by exhaust (just close enough to feel the exhaust flow and not get burned)
if its missing you should feel the exhaust pulse change.

also check that your air filters are clean and not restricting air flow. (commonly over looked)


on a side note:
you can also check for bad gas by pouring gas into a clear jar, let it sit awhile then check for water content.
(water will separate from gas, the water will be at the bottom of jar)