50 Johnson lean sneeze!!

[Rodman738]

I recently did a power head swap on a 1988 Johnson 50 Hp tiller.
It has a lean sneeze or backfire at lower rpm that sometimes stalls the motor.
I have swapped power pack,coils, ignition sensor,carburetors, plugs.
There isn’t any lean adjustment on carburetors and the small orifice is clear on both carbs.
Any advice would be appreciated!

 

[jimmbo]

Could be a leaky Gasket between the Carb and Intake, and/or a leak between the Intake and the Crankcase. Link and Sync out of adjustment. Low Float Level, bad Gaskets in the Carb, dirt/Gum/Varnish in the carb circuits, to name a few

 

[racerone]

Where did the replacement powerhead come from ?----Are both throttle plates closed at idle ??----If they are not closed , the idle circuit does not work.