Janicholson...quick question

Jim, I was running the M today and I noticed that at idol it seemed to idol up and down on its own, nothing crazy but I noticed it wasn't consistent...any ideas? Thanks, Anthony

The two most common issues are looseness in the throttle linkage Enclosed in the tube on the M and not normally a problem, and Idle mixture adjustment. The idle mixture screw is located near the mounting flange of the carb. Screwed out is lean screwed in is richer. Idle speed needs to be adjusted at the same time to get the sweetspot of slow smooth idle.
One other issue can be involved and that is distributor cam bushing wear and thus variable point gap. the bushing must hold the rotor with no radial play (not in and out). If it is a magneto, it will be rough if the timing is correct, as there is no centrifugal advance on a mag. Jim

I'm leaning to the idle mixture adjustment only because I set it per the manual a year ago and haven't touched it since, is it just a matter of putting the throttle at 1/3 throttle and slowly adjusting one way or the other until it runs smooth? My ignorance but what does lean/rich refer to, air or fuel/air mixture? Just attempting to understand why its doing what its doing. Thanks for the help, Anthony

Idle (as in- as slow as it will run with the throttle lever pushed forward) is affected by the idle mixture screw. Any increase in engine speed above maybe 750rpm will be un-affected by the idle mixture screw.
The carb runs on the main jet passages and nozzles when in mid rpm ranges. That mixture is adjustable with the load screw (bottom front).
A perfect mixture of fuel and air is between 14 and 15 to one ratio. The best a carburetor can do is to attempt to make that happen based on temperature, external air pressure (varies with altitude) and applied vacuum at the discharge ports in the carb. The highest vacuum above the throttle plate is applied at low speed idle. (the throttle plate is closed to its stop, and restricting the air flow. This restricted flow is so small that the main jet has no flow of air past it and no vacuume is applied to the main nozzle. (all the vacuum is on top of the throttle plate, pulling fuel through the idle circuit.)
At higher speeds the air flow past the venturi (where the main nozzle is located) causes vacuume there pulling proportioned fuel into the airstream. At full throttle and full load, the throttle plate is wide open, and the fule is pulled from the main jet, and load screw, and discharged out the high speed nozzles in the venturi.
Your updraft carb is similar to the ones shown below, but upside down.(makes no difference)
yours will not have an accellerator pump, nor a hot idle compensator, nor a power circuit. it is more basic.
Your idle richness adjustment bleeds in more air as it is screwed out, and less fuel. Many adjust the opposite way more fuel out and less fuel in. I hope this helps. Jim
Basics pics and discussion

sweet, thanks jim, I appreciate you taking the time to help me. ~Anthony