Re: Johnson QD12 10HP carburetor problem

First, Make sure the selector switch near the tiller arm pivot is set to "OFF" before making any attempt to dial in carburetor adjustments on an early QD.

In my experience these carburetors on the early QDs (QD-10 thru QD-14) do not transition thru mid range as smoothly as the later carburetors. They do fairly well once they are dialed in but do not seem to have as smooth of a mid range as the later ones (assuming the idle and high speed are set for best running). This seems to just be a characteristic of these motors.

It seems that to smooth out the mid range the low speed ends up too lean for a smooth idle and the engine tends to stumble if throttle is applied too rapidly. Set it for a good idle and tune out the stumble and mid range gets rough again. I have three of these motors running well now (QD-10, 13, and 14) and they all exhibit this behavior. If anyone knows of a way to tune this out, I’m also interested.

-Ben