carb adjustment

[Roby L. Baisden]

I have a Ford 601 Workmaster and I am having carb problems(burning too rich). Can anyone tell me how to adjust a Marvel Schebler carb?

 

[Bill Radford]

You basically just have to worry about 3 things. If you have the original M/S Carb, you will have three adjustments: Do these with the engine at normal operating temperature.
Please be sure that your carb is clean and in good working order first.clogged up passages and air leaks around the throttle and choke shafts can make the thing impossible to adjust properly

First, on the engine side of the carb you will find the idle stop screw. Close the hand throttle all the way and adjust the screw with a sraight-head screwdriver until the engine idles at around 500 rpm.You may want to set the idle speed just a bit higher if the tractor cuts off at the low idle.
The idle air adjustment needle is on the top of the carb , this is the smaller of the two adjustment screws on the outboard side of the carb.
Turn this adjuster clockwise until it gently seats. (Too tight can damage the needle seat and it wont adjust properly) Adjust the screw out (counterclockwise) for one full turn. Start her up and turn the adjuster in or clockwise until the engine starts to "roll" or vary up and down slightly with respect to RPM.Back the needle out (counterclockwise) until she smooths out.
Your idle rpm may have changed after you made this adjustment, if so, go back to the idle stop screw and adjust to the desired rpm.
The main jet adjuster is the larger of the two adjusters on the top of the carb. The owners manual says to make this adjustment under load. Unless you can hang off the side of the machine while plowing, this is not an easy thing to do.
Most folks say to do the adjustment starting with the adjuster slightly over 1 turn out from seated.
What I did was increase the engine speed to about 2000 rpm then set the adjustment to where it runs smoothly. If you are too lean, it will stumble, too rich and you will get black smoke when you crack open the throttle.
Run the tractor for a bit then pull the plugs and have a look. You dont want to see a lot of black.. you may want to put in a new set of plugs if you have been running really rich because they will be fouled with carbon and you wont be able to really read them . What you want is a mix of white and light brown on the insulator of the plug.
You will want a manual. You can get one on this site or you can get one from your local Case-New Holland dealer. It will pay for itself many times over.
Have fun!
Hope this helped.

 

[souNdguy]

rich?

make sure spark is good first.

check for vac leaks. that all good.

screw the main needle in a hair.. check idle air needle

 

[Roby L. Baisden]

My engine is leaving a black smoke but it starts so easy and has all the power that I need but with the engine running you can't stand behind it. It will absolutely burn your eyes out.

 

[Bill Radford]

check the second adjuster I told you about, then check your air filter and intake for obstructions. A local gentleman had a John Deere act this way and there was a bird nest in the intake.

 

[Geo-TH,In]

My IH C has only one adj screw and is backward carb adjustment. When you turn the adj crew inward, the mix gets richer. I THINK, my jubilee has 2 adjustment screws. The smaller idle screw is like normal, inward = lean. The larger main screw is like the IH C, inward = rich. Experiment and post back.

You plugs will tell the story. Both my tractors have clean gray plugs, need a choke to start and run for a short time, and when working hard, needs a short cool down time or it will diesel.

That tells me it close to the right mix, not to mention it uses less gas.
George

 

[Roby L. Baisden]

The plugs when I check them are carboned up bad. I checked my adjustment screws and I have two. There's one small and one large. The large one is right in front of the carb.

 

[Geo-TH,In]

Sounds like the same carb I have on my 1953 jubilee, which is think your old tractor's older sister. Had the same issue when I bought my IH C, which only has one adj. Plugs were black, indicating rich mix. The adj screw was all the way in. Then I read up on the carb adj and it said all the way in was rich. I ended up turning my adj screw so far out, had to put two small washers under spring to hold adj in place.

Again, I'm thinking my jub carb, the big adj is the main adjust, and the more you crank it out, the leaner. The smaller screw is the idle adjust and all the way in is leaner. On my ford, if you go too lean, the engine when warmed up will stumble when up under a load at high speed. It will also stumble more in the winter.

My jubilee will take about 2-3 minutes to warm up, so I don't put it under load and up the RPM's.

I bought a cheap sand blaster from harbor freight to clean my plugs.

Did you try adjusting the large screw out and the smaller screw in? Adjust the small screw at an idle and the larger screw at 1500 rpms. Then watch for a stall when the governor open under load.

George

 

[Roby L. Baisden]

I also bought me one of those sand blaster plug cleaners. I have two adjustment screws beside the idle adjustment. If I backed the big one out very much, it will stall the engine. I'm assuming the small screw is air mixture.

 

[Geo-TH,In]

Not exactly sure how the carb works, but backing the large screw out, causing it to stall, means you are leaning it out. Keep in mind, the large screw is for high speed mix. The small screw is for adjusting the idle mix. The two will have a small influence on each mix.

Keep up experimenting, you will find the balance.
George