Case SC with Zenith Carb

mmikey45 · Aug 6, 2017

I have a 1949 Case SC with a Zenith carb. Tractor has become almost impossible to start. It only starts with full choke and no throttle added. Once started I can slowly add throttle and partly reduce choke. The
tractor stalls if I add any type of load to it. Have tried adjusting the fuel needle valve. This has not made a difference.Could this be ignition related and not carb?

Indiana Ken · Aug 6, 2017

When you adjust the fuel needle, does the engine run better or worse? If there is no change, it suggests the problem is carb related....main circuit/jets in the carb are plugged.

mmikey45 · Aug 6, 2017

the only time adjusting the needle valve makes a difference is when closing it out. Which causes engine to starve.

old · Aug 6, 2017

Do these simple trouble shooting things.
#1 check that you have a good blue white spark at the center wire of the cap and at all the plug wires that will jump a 1/4 inch gap or more. If you do not have that check points etc.
#2 pull the carb drain plug out of the bottom of the carb and check to see if you have a good gas flow that will fill a pint jar in less then 3 minutes. If you do not have that work your way back to find where it slows down. And yes catch the gas to check for water/dirt etc. By the way does your carb have one or 2 adjustments?? If it has 2 the top one is idle and the lower one is the main jet and if all is well you should be able to open up the main till you get black smoke.
#3 when was the last time you serviced the air cleaner it could be full of mud and water.

Steve@Advance · Aug 6, 2017

It could very well be ignition related.

By full choking and closing the throttle, you are restricting the available air to be compressed, therefore lowering the cylinder pressure. That allows a weak spark to jump the plug gap.

Once it starts and the choke opened, it will idle until the throttle begins opening, then the compression increases, and the weak spark fails.

Just a theory, it could also be fuel related, but spark would be a good place to start.

Is this magneto or battery ignition?

D beatty · Aug 7, 2017

If you have good spark it has to be carb. Check fuel flow to carb and the fuel filters.Check fuel tank for any crud floating around bottom of tank plugging outlet. If all of the above is ok then the carb. needs a good cleaning and rebuilding..

mmikey45 · Aug 7, 2017

(quoted from post at 20:30:50 08/06/17) It could very well be ignition related.

By full choking and closing the throttle, you are restricting the available air to be compressed, therefore lowering the cylinder pressure. That allows a weak spark to jump the plug gap.

Once it starts and the choke opened, it will idle until the throttle begins opening, then the compression increases, and the weak spark fails.

Just a theory, it could also be fuel related, but spark would be a good place to start.

Is this magneto or battery ignition?

This tractor is magneto. I think it is a Wico mag. It does not have the case eagle on the side of the mag,

D beatty · Aug 7, 2017

Are you sure that its not an American Bosch mag.?

fixerupper · Aug 7, 2017

The smallest piece of junk will stop up the carb on my SC. That's why I now have an inline filter between the sediment bowl and carb. Try completely removing the load screw from the carb. It might take a 5/16" end wrench to unscrew the packing nut. Sometimes the gas flowing out will back flush the load jet. This trick has helped me get home a couple of times.

Case SC with Zenith Carb

mmikey45

New User

Indiana Ken

Well-known Member

mmikey45

New User

old

Well-known Member

Steve@Advance

Well-known Member

D beatty

Well-known Member

mmikey45

New User

D beatty

Well-known Member

fixerupper

Well-known Member

Similar threads