Ford 4000 gasoline 1972 running rough

Hi!

You guys have helped me so many times in the past so I thought I'd come to you again.

My tractor runs rough. Choking improves the rough running but when I throttle down to an idle, it dies. Any ideas on what I might do to fix this?

Thank you in advance!!

Is the bottom of the carb wet? The float gets stuck and I have to pull the drain plug on the bottom of the carb and with a wire or something and pock at the float.

I gotta ask:
Is it a Holley carb or a replacement?
Is the original fuel system still
intact?
By the way, I still always check my
spark first - even if I'm pretty sure
it's a fuel problem.

Thank you both so much! You've given me
some ideas that I can try out.

I don't really know what kind of
carburetor it is but I have never replaced
it and I have had it for 35 years. It just
got all new spark plugs and wires two or
three years ago. It had been running great
until about a week ago so I'm just
grasping at straws here and you have given
me some things to try. Thank you.

Always verify that the ignition is spot on before looking to carburetion, even if your experience tells you otherwise.

"Running rough" (missing) is generally (I did not say always) caused by faulty ignition, but it is nearly impossible to diagnose such symptoms in a chat forum.

Is it flooding? Black smoke? If so, look to float level. The OEM Holley carburetor is very sensitive to float adjustment.

Does it stumble only upon tip-in (throttle up)? If so, look to the vacuum operated accelerator pump and the usually defective vacuum advance motor, which affects intake manifold vacuum.

Many folks, herein, do not like the Holley carburetor used on Ford tractors but it was a very good carburetor in it's day, and quite simple as compared to contemporary automotive carburetors. Should you decide to rebuild yours, bite the bullet and buy your overhaul kit from a CNH dealer. Insist upon the expensive genuine CNH kit rather than an aftermarket kit and pay close attention to the float level and float drop adjustments. Be certain to take both tractor SN and carburetor SN with you when you visit your CNH dealer to order your kit (they will NOT have one in stock) and insist upon speaking with an experienced parts person.

Finally, disassemble your carburetor before ordering your kit. Some (many?) Holley carburetors cannot be cost effectively overhauled due to, e.g., corrosion damage. If this is the case with your carburetor, you will need to replace it with a Zenith.

Dean

Thank you for all the great information
And please excuse my ignorance but what is 'CNH?' Thanks, again, in advance.

Case New Holland, brand

Thanks, again.

Sometimes the choke or throttle butterfly shaft/or bushing gets worn and allows air in to upset the mixture. If the float and everything else is okay you can temporarily check this by dobbing heavy grease (ear swab)on the both sides of the shaft while it is running to seal the leak if that is what is going on. The tractor is 35 years old.
An alternative is to take a propane torch, turn the propane on and run the unlit head around the carburetor and intake gaskets to see if it affects the idling engine.(raise the idle enough to keep the engine running.) This is a check for gasket leaks, throttle leaks, and warped intake manifolds.