[Farmall] Zenith Carb Adjustments

[Barney Van De Weert]

>From what I have read in the O-M, the main or load adjustment is about 4 turns 
out, the main jet then controls the fuel mix for a full load. If you want to 
save fuel you can adjust the main load screw in. That is the one at the bottom 
of the Carb that does not have a spring on it. I have both an A as well as an H 
they are both set the same way. When the engine comes off a full load situation 
it does puff a little black smoke. If you want to down spec it you can then 
begin to adjust the main load screw in a little at a time.

The idle adjustment regulates a small amount of fuel out of the fuel bowl, I 
tune mine in untill the engine runs rough, then open until it smooths out and 
begins to run rough again. I then turn it back in until it smooths out and runs 
the best. It does take a little time for the fuel mixture to even out so adjust 
slowly.
 Barney Van De Weert 




________________________________
From: E. John Puckett <ejpuckett at centurytel.net>
To: Farmall/IHC mailing list <farmall at lists.antique-tractor.com>
Sent: Tue, July 12, 2011 9:00:33 AM
Subject: Re: [Farmall] Zenith Carb Adjustments

Ben, the idle speed screw Mike is referring to is normally mounted on 
the arm where the governor linkage connects to the car and moves with 
it,  His instructions are pretty much on.  A little trick on the load 
(bottom ) adjustment is set it where it runs best at full throttle and 
turn it slightly richer (1/4 turn or less) so it will have the fuel 
needed under a load.  You can fine tune from there.

On 7/12/2011 8:20 AM, Mike Sloane wrote:
> 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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