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b72 Johnson 25 hp coughbackfire

boatdave

New member
"I have a '72 Johnson 25 h

"I have a '72 Johnson 25 hp that will cough or slghtly backfire at the rate or about once every minute at all times, at all speeds, even after it warms up. The low speed jet seems to function normally, letting me overly lean and overly richen the mix, yet this will not fix the problem that I would normally associate with a lean idle mix. also I am finding no air leaks around the block. I am using the same fuel, tank, and line with other motors with no problem. Otherwise the motor runs great. What's up?"
 
"The throttle butterfly must o

"The throttle butterfly must open exactly when the scribe mark on the cam, the cam that rides against the throttle roller, is dead centered with the cam roller. If it is set where the butterfly opens too soon, what you describe will take place.

This is assuming that you are correct in that the carburetor is clean and the slow speed needle valve is adjusted properly."
 
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