Re: Johnson 5hp TD20 ignition timing facts & figures?

[legendre]

quote Jim Moffatt:

I had forgotten this. If the throttle butterfly doesnt close properly and completely it will do just what you have experienced.
Sometimes the butterfly will create a lip in the air tube where it seats. The extra air causes it to die.
I dont think this is an ignition problem.

The throttle linkage on this motor was broken, the longer of the two shafts snapped-off near the middle drilling. I made a dang-near perfect copy using 1/8" brass rod and the throttle rod from my good runner as a pattern. As far as I can tell, the main butterfly opens & closes when it should – and no, there’s no notch worn in the carb bore.

I did have some major air leaks between the manifold & block, and also between carb & manifold. But I believe I’ve corrected these – we milled / lapped-flat the manifold and carb flange surfaces. Also, both got brand new gaskets (made them myself from 1/32" Fel-Pro black rubber-fiber material).

Correcting these leaks did make a notable improvement in overall running, but the low-throttle setting issue was almost totally unaffected.

Candidly, I don’t think it’s ignition either, but I want to rule that out for sure before I chase more exotic things..