For the mixture, describing the adjustments will depend on whether you have a gas or a dual-fuel carb. Assuming it's gas, there shoul dbe only two adjustments, idle mixture and idle speed. Idle mixture is a knurled screw with a spring under the head, and probably near the neck of the upper part of the carb where it goes up to the manifold, pointed slightly downwards. Rule of thumb is to have the tractor warmed up and running at idle. Shut it down, turn this screw all the way in (DON'T force it hard into the bottom of the thread!) then back it out 1-1/2 turns as a starting point, and restart the tractor (no choke necessary at this point!). Adjustments from there are pretty much by ear and from experience, to get it to a nice rolling idle (more on which in a mo). If you feel your ear or experience are lacking, one tip would be that you shouldn't have any black smoke at idel, and a minimum of black smoke, if any at all, when you throttle it up quickly from idle. Black smoke would be an indication of idling too rich. If your carb is like most (ba no means all) of them here, you would thread the screw in by quarter turns to eliminate the smokeing condition.
Idle speed adjustment (which is unrelated to the mixture adjustment) is made at the linkage from the governor to the throttle plate, usually located in a very inconvenient spot between the throart of the carb and the crankcase. On mine, with a Zenith carb, it requires a VERY long screwdriver passed from the rear through on eof the openings in the bracket mounting the air cleaner to even get to it. No real easy rule of thumb on a starting point as with the mixture screw. The best advice I can give in a nutshell is to turn the screw until the motor wants to die from starvation, then undo a little bit.
It will take some fiddling, but there is a balance to be found between the idle speed and the idle mixture that will give you a nice idle.
The mixture at high idle and under load is determined by the condition and cleanliness of the small orifices in the carb body.
Short version, low idle speed and mixture are governed by two screws on the carb. High idle speed is controlled by the governor, and the high idle/load mixture is a function of having a clean carb.
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Today's Featured Article - The Cletrac General GG and the BF Avery A - A Bit of History - by Mike Ballash. This article is a summary of what I have gathered up from various sources on the Gletrac General GG and the B. F. Avery model A tractors. I am quite sure that most of it is accurate. The General GG was made by the Cleveland Tractor Company (Cletrac) of Cleveland, Ohio. Originally the company was called the Cleveland Motor Plow Company which began in 1912, then the Cleveland Tractor Company (1917) and finally Cletrac.
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