Re: 9.9 Johnson Carb Question

[Don]

The symptom you describe was a common one on many of the older 9.9/15s I worked on: The engine would fall flat/maybe stall while decreasing the throttle slowly and the engine was relying more on the idle circuitry. I usually had to readjust the idle mixture a tad rich to compensate. Your throttle pick up is a bit late/retarded (.010 between roller and cam at pick up point), but this would cause the opposite condition: rich at midrange. The only other thing I remember is that some of these earlier throttle linkages were prone to sticking (throttle plate not closing/sticky), this can be due to all the crazy add on safety linkage. So, just because there is a gap between the roller and cam does not mean the throttle plate is closing completely.
So, does the engine idle OK now? Is this midrange thing the only problem? If idle is still NG, I would look for a different carb to try. If the engine idles OK with a different carb, then we can dig deeper into this carb…