Carburetor main adjusting needle adjustment?

Folks recently rebuilt my carb on 1964 Ford 2000 4 cyl gas tractor and now need to dial it in. Got idle set no issues. Now the Ford shop manual says to bring engine up to operating temperature, remove any three spark plug wires, open the throttle to full throttle setting and adjust the main needle until highest operating rpm is obtained. Is that right and is it they simple? Just seems a bit odd to pull 3 sparkplug wires off and reave it up?

I would not follow that procedure.

Open throttle suddenly, if it stumbles open up power valve.

You're going to get a lot of opinions here. Adjust the idle needle to get the highest RPM then set the idle speed. Sometimes you have to go back and forth. After the
idle is set go to wide open throttle and adjust the load needle for the highest RPM. Close the needle till the speed starts to drop them open it till it starts to drop
again. Set it halfway between or just a bit richer. If it stumbles when you open the throttle quickly richen the idle mixture a bit at a time till it doesn't stumble.

That seems very odd to me. I've never seen any carb adjustment
procedure say to remove the spark plug wires. Certainly never
seen it for a Ford with a Marvel Schebler carb.

I agree with the others as to yanking the throttle open. If it
stumbles it needs more adjustment. But that main adjustment
shouldn't need to be open much more than two turns or there's
something wrong/plugged in the carb.

On the MS carbs, if you change the main adjustment, it will likely
change your idle adjustment too. The idle adjustment adjusts air
to match the fuel coming through the carb. That why "in" is enrich.
Out is leaner.

The adjustment procedure is usually something more like this.
This is from the 601/801 manual. One model older. Same engine:

That's got to be the dumbest advice ever
put in a manual. The carb feeds 4
cylinders, not 1. And no one is going to
run alongside a tractor while under a
load and adjust the carburetor. Not
gonna happen. That only works with a
dyno which most people don't have.

There is two ways to set up your
carburetor with your ears. Get the
engine to operating temperature first.

For power - adjust the load needle until
it runs smooth. Ease the needle out
until it starts stumbling. Ease it back
in until it just smothes out and stop.
This is considered a rich working
setting.

For a lean puttering around - adjust
the load needle until it smoothes out.
Ease the needle in until it just starts
to stumble. Ease it back out until it
just smoothes out and stop.

Yes you will probably need to readjust
the idle screw afterwards. Listen
carefully and turn the screws slowly and
you will be fine.

Sssoooo basically get it up to operating temperature, raise rpms up to highest working rpm then dial it in. Adjust
Idle as needed.

So folks know I wasnt lying and its in print. Manual is I&T Shop Manuals Ford FO-20.

(quoted from post at 19:56:27 11/30/20) That seems very odd to me. I've never seen any carb adjustment
procedure say to remove the spark plug wires. Certainly never
seen it for a Ford with a Marvel Schebler carb.

I agree with the others as to yanking the throttle open. If it
stumbles it needs more adjustment. But that main adjustment
shouldn't need to be open much more than two turns or there's
something wrong/plugged in the carb.

On the MS carbs, if you change the main adjustment, it will likely
change your idle adjustment too. The idle adjustment adjusts air
to match the fuel coming through the carb. That why "in" is enrich.
Out is leaner.

The adjustment procedure is usually something more like this.
This is from the 601/801 manual. One model older. Same engine:

Click to expand...

Yeah Id read that before somewhere as well plus the carb rebuild kit had same instructions for adjustment. Thing is never figured out what/how to run tractor at full load AND adjust carb at same time without running myself over.

I'm guessing your "Ford" manual is actually an I&T manual. My Ford factory shop manual (covers 600 series up through four cylinder 4000) has the same adjustment procedure that Royse showed, except it says to start "1-1-1/4" turns out rather than than 1-1/8. (I assume they meant to say "1 to 1-1/4 turns".)

Pulling three plug wires to set the main jet seems pretty goofy, but is it really all that preposterous? I don't think so. First, the only right way to adjust the main jet would be under dynamometer load. But not many farmers own a dyno. So you want to simulate heavy load conditions: Low manifold vacuum (aka high manifold air pressure), high carburetor airflow, and high engine torque. If you pull three plug wires and open the throttle all the way, you'll have low manifold vacuum and reasonably high airflow through the carb. Even though the three dead cylinders aren't putting out any power, they're still pumping air. The engine isn't putting out any torque, but the dead cylinders do present some load to the single live cylinder. I think it sounds like a reasonable way to set the main jet without a dyno or similar PTO load.

As for setting the main jet to eliminate "stumble" on acceleration, unless a carburetor has an accelerator pump or is a constant velocity carb, there's always going to be a slight stumble when you suddenly open the throttle. If you try to eliminate it, you'll probably end up with a rich mixture.

On the other hand, if you try to adjust the main jet at high speed but no load, the idle circuit will probably still be in play, enrichening the mixture. You're likely to end up with a too-lean setting when the engine is under load.

What I don't understand if you disconnect 3 cylinders & have only 1 cylinder how will the engine run ? Dave F. 54

(quoted from post at 22:07:26 12/01/20) What I don't understand if you disconnect 3 cylinders & have only 1 cylinder how will the engine run ? Dave F. 54

Click to expand...

Might stay running if you pull them off while it's running.
Seems like it would be hard to start that way though.

> What I don't understand if you disconnect 3 cylinders & have only 1 cylinder how will the engine run ? Dave F. 54

Speaking from experience, four cylinder Fords run pretty well with only a single cylinder firing.