Farmall bn starts but has rough idle.

Ok need the pros to help with my problem. I have a Farmall bn 1944. I was aware of the rough idle when I bought it. I have replaced the spark plugs and new wires. I have also replaced the 6 volt coil with new points and condenser. I have cleaned and checked the air breather. I have removed the carb and rebuilt it with new gaskets and cleaned jets. I have even checked for leaks around the carb with carb cleaner did not change anything. I have even tried to smooth out the rough idle by turning the distributor no luck. After doing all of this the tractor does run better but it still has a rough idle. The idle is sort of like increasing and decreasing the idle by pushing the hand idle lever control. The spark plugs were pulled tonight and each spark plug was solid with black soot. When I start the tractor I see some soot shoot out of drain holes on bottom of manifold. I also have soot that shoots out muffler. I can drive tractor around and it won't die it just sounds rough I want to hear it puuuuuur. Thanks

Black and soot on the plugs mean it is running way to rich so you either have a carb problem or an air cleaner problem or the plugs are to cold of a type of plus

Have you checked the valves? If they open and close improperly because of poor adjustments, it will not run as smoothly as it should. Another problem could be the throttle shaft being worn in the carburetor and the same with the distributor shaft being sloppy.

No compression check?always on any tune up. Even a
valve setting should be done. Plus your moving the
distributor, so that means then timing is not set. U need
to have the timing set before u can adjust the carb. U did
not say or give your carb settings. Plus it appears its
surging so it might also need governor linkage set. How
was the carb cleaned ?did u totally disassemble it and
soak it in gunk? Might have the idle circuit plugged. A
person needs pretty detailed info when trying to come up
with a fix to the problem. I Know any of these engines
start with one plug firing or 1/2 a revolution when they
are tuned up to factory specifications.and they run so smooth at 400 rpm idle you can hardly hear them running.

Sounds to me like you did not get a passage cleaned in
your carb. Pull it apart and get a wire to poke through
EVERY passage. Then a squirt of spray carb cleaner
followed by a blast of compressed air. Do them once
and then do them again. Also to check for vacuum
leaks you need to spray along the entire manifold
where it bolts to the head.

I would start with adjusting the valve lash, and a valve train inspection. Look for broken valve springs, bent pushrods, watch that all the valves are opening and closing.

Then run a compression test. Don't worry so much about the amount of compression, but look for differences between cylinders. Ideally they need to be within about 10% of each other.

When you had the carb apart, did you check the float for buoyancy? Did you set the float level? Does the carb drip gas if the fuel valve is left on? Did you adjust the main jet? How is the fuel supply? If the tank is contaminated or flaking rust, you will have ongoing carb problems. It needs a clean, reliable source of fuel to function properly. Any of these things can lead to rich running, but before blaming or adjusting the carb, everything else must be in order.

I'm not aware of any engine that has drain holes in the exhaust manifold. Makes me wonder if possibly the manifold is burned out. Some are designed as a one piece intake and exhaust casting. On those, the exhaust can burn through internally and enter the intake side, which causes them to run terribly, similar to a vacuum leak but worse!

I'm new here and don't know anything about tractors but I am a retired mechanic,
Black sooty plugs means too much gas or not enough spark, in adddition to what others have said, how is the fuel tank, full of rust. Could some of it be getting between the needle and seat, flooding the carb? You'll likeky end up with fuel in the engine oil, does the oil smell gassy or is overfull?
The other thing that pops in my mind is weak valve springs. Kind of hard to test them unless the heads on the bench but a vacuum gauge might show "fluttering"

After all this .... I would put a vacuum gage on it.

bought all those new parts when the first thing always is COMPRESSION
CHECK. the reading wants all the cycls close to the same what your figures
is subject to the guage, temp and how many compression strokes were
measured

I agree with carrol. Put a vacuum gauge on it and see where you're at.