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1979 Mercury 40hp 402 2 cycle

You need to rebuild the carb. Clean thoroughly and reassemble using new gaskets, needle and seat. Be sure to check the float while you have it apart for fuel intrusion and adjusted properly when reassembling.
 
You can hand pump that carb to 15 pounds pressure, where the motor only develops 4. Most carbs will do that if you pump too hard. Long as it doesn't leak when the motor is running it's okay.

Jeff

PS: I lower the float level 1/8 inch on mine when it does that.
 
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