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Mend Briggs & Stratton 10D902 Lawn Mower Engine Spark Plug

How to resolve uneven engine beat on Briggs & Stratton Champion 375 lawn mo?

My Briggs & Stratton Champion 375 self-propelled mower starts first time and keeps going but the engine note is "Vroom-vroom-vroom" instead of steady. The butterfly valve is opening and closing. The throttle is fixed so the engine speed is not variable manually. The model number is 10D902 and type 0153 B. It is 3.75hp and has a 46cm blade. The spark plug is BR2-LM. Can find nothing relevant in the manual. Can anyone help please?

Whyard
September 2012

Briggs & Stratton Briggs & Stratton 10D902 Garden Tools, Lawn Mowers Lawn Mower Engine Spark Plug

Problem resolved. Thanks Roger for the attempt, and the problem was due to an air leak, but not in the carburettor diaphragm. The carburettor glides over a sleeve protruding from the cylinder barrel and the annular gap is sealed by a rubber "O" ring held in place by a plastic ring just inside the carburettor orifice. The ring had become displaced, allowing the "O" ring to move out of position and thus admitting air giving rise to the irregular engine note. When the seal was put back in place, the engine ran smoothly once more. Tip: reconnect the hair spring above the carburettor before reattaching the carburettor to the cylinder barrel - it makes life much easier than trying to connect it afterwards.

Whyard
September 2012

My Briggs and Stratton had the same fault it was located to a perforated diaphragm in the carb

Roger
September 2012