runs poorly

Tractor pros, I have a 1961 Massey Ferguson 35 deluxe. About 6 years ago I had it repainted and tuned up and hoses, etc. replaced as needed. I have had this machine for about 10 years. After the refurbish it has run without fail as perfect as possible until a few weeks ago. Then it would quit and then it would not run unless the choke was out and it would not idle. I think you get the picture. After removing the carb and tearing it apart it showed the float was frozen with corrosion to the bottom. I bought a new cast iron replacement and put that on. It will idle about 1,000 RPM and the idle screw is way back. If I try to move the throttle back it dies. I had it running for a half an hour today and even under a slight load ( snow plow ) but then it starts to spudder and fart and will just die . I have checked filters, screens, fuel is always fresh high test no ethanol. What may anyone suggest I check next ? I suppose it is possible the new carb is defective ? Thanks, JZ

clean the old one. There is little that can go wrong with one

There must be a continuous flow out the carb drain (if it has one) of a pint every 2 minutes. It needs to flow for at least a minute with continuous stream, or the lines, tank fitting, or screens are plugged up. Jim

A couple things come to mind...

Just to say you did it, check the ignition system. Check the points
condition, gap, distributor shaft for side play, the centrifugal advance
function, wires and plugs. Check the spark quality at the plug end of
each wire. It needs at least 1/4 inch spark to ground to run properly.

Also, have you checked the valve clearance? Any chance the compression is
down? The carb can only work as well as the rest of the engine. It's a
pain to set the valves, the gas tank has to come off, but it's necessary
to keep everything in tune. The compression needs to be at least 90 PSI
and somewhat equal between the cylinders.

Back to the fuel system. In order for the old carb to have been rusted
and corroded internally, there had to have been water in the fuel! Unless
the tank has been removed and cleaned, there is still a water problem.
And while the tank is off, see above!

There is a drain plug in the bottom of the carb bowl. with the engine
off, fuel valve open, get a clean glass, remove the plug and catch the
flow. First, it should have a full flow of fuel, the flow should continue
as a stream, not slow to a drip or stop. Look at what was caught. if you
run non ethanol gas, any water will be on the bottom of the glass. So
will any sediment, trash, or rust. If you have a dirty, rust flaking, or
water contaminated tank, the same will be in the carb, and will be an
ongoing problem until it is addressed. Nothing more frustrating! If the
tank is flaking rust, the easiest solution is to buy a new replacement.

If the carb is contaminated, it is easy enough to open it up and clean
it. Usually the gasket can be saved and reused.

As for adjusting the carb, which needs to be done last, after everything
is right and all problems corrected, then it can be successfully
adjusted. You say it refuses to idle below 1000 RPM, that is a clue there
may be a compression problem. The engine should easily idle well at 400-
500 RPM, and it must be idling that slow for the idle adjustment to be
effective.

The idle mixture adjustment, (the small screw up above the throttle
plate), is really an air bleed adjustment. Turning it in richens the mix,
backing it out leans the mix. It has very limited overall effect. So,
with the engine up to temp, idle adjusted down to 400 RPM, turn the screw
out until the idle gets rough, then back in until it idles best.

The main adjust, (the large knob type screw on top of the bowl cover),
adjusts the main jet flow. Start with the screw about 2 turns off the
(gently) fully screwed in position. Let the engine idle down to slow
idle, then suddenly open the throttle and listen to the response. When
properly adjusted the engine will take sudden throttle without
hesitation. Keep repeating the test, turning the screw in 1/4 turn until
it stumbles on acceleration, then back it out 1/8 turn at a time until it
takes throttle responsively. A single puff of black smoke is desirable.

Hope this helps, let us know!

I just went through this exact problem with a 1958 Massey
Ferguson 35. Made sure the tank was clean and delivering a
strong flow of gas. Tried a new carb - didnt help. Cleaned the
old carb - better, but not fixed. Turned my attention to the
ignition- replaced the points with the best ones I could find -
Blue Streak - ran great like it always has! So, if youve been
through the gas system, Id recommend working on the ignition.
I would also recommend keeping all your old parts which
generally are better quality than new ones. Cleaning and fixing
the carb isnt hard - I did it and Ive never had a carb apart
before - and I feel much better having that one back on there
than I did with the cheap Chinese one on there! It has a 60 year
track record of excellent performance!