1969 Evinrude 40 HP Big Twin, Lark Service Repair Manual P/N 4596, Page 15Get this manual
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TROUBLE CHECK CHART (CONT) TROUBLE POSSIBLE CAUSE APOWER HEADSee Section Throttle control lever bent (won't advance) Air leak at manifold gasketswarped manifold (backfires) Broken eed valves (backfire