[AT] [Farmall] Zenith Carb Adjustments

[Mike Sloane]

Usually, there are three screws - one of them is just a low speed 
throttle screw, not a mixture screw. You really need to refer to the 
owners manual for the tractor, but I generally start out with one turn 
out on the idle screw and two turns out on the main. The idle jet is 
easy enough to set just by messing with it until you get a smooth fast 
idle, then adjust the throttle screw to get the speed you want.

The problem is that you really have to set the main mixture with the 
tractor running at maximum speed and under load. That is pretty hard to 
do while the tractor is standing in your driveway, unless you have some 
kind of grain mill or generator to run. So I just usually take the 
tractors out and climb a steel hill, fiddle with the mixture, and do it 
again until the engine seems to perform better. If you don't have any 
hills, then I will let someone else chime in with advice...

Mike

On 7/12/2011 8:45 AM, Ben Wagner wrote:
> I have an old Zenith carburetor on my 1945 Farmall A.  It needs to be
> adjusted, since I don't think I'm getting a good mixture.  I see two
> adjustments on the carb; one next to the intake on the manifold with a
> spring, and another below the bowl.  I've adjusted myriads of small engine
> carbs, but never a carb on a tractor.  I think the screw with the spring
> near the intake manifold is the idle mixture, right?  I also think the
> adjustment below the bowl, a little thumb screw, is the main jet mixture
> screw.  I rebuilt the carb about a year ago, and I remember the adjustment
> under the bowl having a long point.  If I am thinking correctly, turning the
> screw in will allow less fuel, and turning out will allow more fuel.
>
> The engine runs like it has too much choke, smoking and gasping.  The choke
> is in as far as possible, so I think the adjustment with the jet will allow
> me to adjust the mixture.  Am I correct?  Do I have any other options to
> adjust the carb?
>
> Thanks!
>
> Ben Wagner
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