Lawnboy 6.5 idles up and down and low power - Briggs & Stratton Lawn-Boy 10640 20-Inch 6.5 HP Gas Powered Lawn Mower

Try a new spark plug and then clean the
carb jets very carefully. Remove the jets
and blow out all the carb passageways.
The jets being plugged cause a lean fuel
mixture which causes the surging.
Last resort is check compression and do a
engine rebuild with new crankshaft seals.
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