Beyond frustrating!

[Aasafetypilot]

Help again! Farmall BN, no power under load… I inherited a mag BN that didn’t run. Did valves, wires etc Now runs great at ALL power settings NOT under load, but under load hunts badly to the point of stalling if I don’t slip the clutch. I have…
Replaced the carb ( no difference from first one. Cleaned fuel lines, bowl, jets etc
Cleaned air cleaner (even ran it with air cleaner off - no change)
Changed timing… no marks found on flywheel, but set at TDC, slightly before, slightly after etc. no change
Rerouted /checked all throttle carb governor linkages..
New springs in governor rod, (2) governor (3) no range
Governor weights free, thrust bearing and small roller bearing ok
What’s left? Magneto impulse? New governor? Spark plugs?
HELP!!! Thanks in advance

 

[wh]

Help again! Farmall BN, no power under load… I inherited a mag BN that didn’t run. Did valves, wires etc Now runs great at ALL power settings NOT under load, but under load hunts badly to the point of stalling if I don’t slip the clutch. I have…
Replaced the carb ( no difference from first one. Cleaned fuel lines, bowl, jets etc
Cleaned air cleaner (even ran it with air cleaner off - no change)
Changed timing… no marks found on flywheel, but set at TDC, slightly before, slightly after etc. no change
Rerouted /checked all throttle carb governor linkages..
New springs in governor rod, (2) governor (3) no range
Governor weights free, thrust bearing and small roller bearing ok
What’s left? Magneto impulse? New governor? Spark plugs?
HELP!!! Thanks in advance

Fought with an H doing very similar. Finally changed plugs. That cured it.

 

[old]

Help again! Farmall BN, no power under load… I inherited a mag BN that didn’t run. Did valves, wires etc Now runs great at ALL power settings NOT under load, but under load hunts badly to the point of stalling if I don’t slip the clutch. I have…
Replaced the carb ( no difference from first one. Cleaned fuel lines, bowl, jets etc
Cleaned air cleaner (even ran it with air cleaner off - no change)
Changed timing… no marks found on flywheel, but set at TDC, slightly before, slightly after etc. no change
Rerouted /checked all throttle carb governor linkages..
New springs in governor rod, (2) governor (3) no range
Governor weights free, thrust bearing and small roller bearing ok
What’s left? Magneto impulse? New governor? Spark plugs?
HELP!!! Thanks in advance

Do you have the firing order correct?? They will run on 2 cylinders and sound pretty good but have no power

 

[used red MN]

They will run on 2 cylinders and sound pretty good but have no power

Sound pretty good? Not in my ears.

 

[used red MN]

Does it seem to have power for a bit 15 to 30 seconds and then drop off? If so that is a lack of adequate fuel delivery. Take the drain plug out of the carb bowl. After the 5 seconds or a bit more does gas continue to flow in a steady stream? It may slow down to a stream the size of a pencil lead but it should not stop dribble a bit and restart the stream again. If you don’t have the steady stream you are not getting enough fuel into the carb. Are you aware of the fine strainer screen on the elbow fitting that the line is connected to the carb by. It needs pulled out to be cleaned, look at number 25 in the link.
CNHI Farmall BN Zenith carb part diagram
Both carb types have them. If you don’t have good flow also check the flow at the line disconnected from the carb, it should flow a good stream the diameter of the inside of the tube. If it doesn’t you need to find the restriction. Often in old tractors that have sat around crud/rust breaks loose in the tank and plugs the top of the sediment bowl inside the tank. Will need to be pulled out to clean. Looking in the fuel fill at the bottom of the tank with a good flashlight will give you an indication of how much crud you might be up against. Lastly if you have added an inline fuel filter most of those are designed to work with fuel pumps. Sometimes on gravity flow systems they restrict flow to much.

 

[560Dennis]

check for there a blockage in the fuel tank supply to the carb. Governor is work trying maintain rpm. I had blockage in sediment bowl inlet not let enough gas flow.
surge
bumper spring is not functioning ,adjusted from bottom of governor.
Surging the bumper spring is broke ,full rust , dirt, not contacting the lever, I usally put a flat headed rivet inside new spring the to make sure it has full contact with lever and does not slip off from past wear, of misalignment.
Are the spring on the governor control rod assembly correct , short spring toward the radiator equalizer spring to the driver .
is the extension spring new in the governor from contol to the lever out put to carburetor. Any wear in the levers hole allows for less response

 

[DaveBN]

To correctly set timing you install the magneto with the top as close to the engine as possible with number 1 cylinder at TDC on compression stroke. Then rotate the top of the magneto towards you until you hear the impulse click then tighten the bolts.
There are two places to hook the bottom of the governor spring to the governor. One place is for a tractor the other is for a power unit, make sure you have that correct. Is the hole in your governor shaft worn where the spring connects as in is it elongated? It should be a round hole. Correct procedure to connect that spring is to have the governor shaft off when installing the spring, don't just bend the spring when installing it.
The two springs on the throttle shaft above the governor need to be in the correct place, the longer spring goes to the rear of the governor linkage.
New plugs or maybe new coil may solve your problem.
Are the points set at .013 for a magneto ignition?
Are the new spark plug wires copper core as needed for a magneto?
Is the distributor cap installed correctly? There is a notch to align it to the magneto base and it should drop into place and fit snuggly onto the magneto.
Keep at it, you'll find the problem.
Dave

 

[BarnyardEngineering]

To find TDC on a Farmall B/BN, remove the front spark plug. Put a finger or thumb over the hole and bump the starter until you get a whoosh of air. Remove your finger, and shine a light down in. Turn the engine over carefully by hand until the piston goes up as far as it can and starts to go back down. Work the engine back and forth until the piston is at its highest point. Now you are on TDC and can continue with timing the ignition.

Have you checked compression?

 

[Aasafetypilot]

Thanks to all who have responded! Very insightful. Today and tomorrow I’ll be repeating many of the suggested fixes and working on the new ones - will update with results. Thanks again!

 

[rustred]

Sound pretty good? Not in my ears.

That would be like the john Deere 2 bangers going pup pup pup. Lol.

 

[DaveBN]

Hint-you can move the engine in small increments by bumping the fan blades with the palm of your hand. It's easier to do that with the plugs out and easier yet if you have a helper. The timing marks are on the back side of the flywheel and you need to remove the inspection cover under the torque tube and shine a light forward towards the flywheel. You'll need a helper then also to turn the crank until the mark on the flywheel lines up with a tab on the cover In front of the flywheel.
Dave

 

[560Dennis]

Spay some carb cleaner around the carb and the intake manifolds ,if the rpm increases you have a vacuum leak to correct then .

 

[Aasafetypilot]

Hi everyone. Thanks again. But… still frustrated.
Compression 90-100 on all cylinders. New plugs. New copper wire ignition wires. No induction leaks. Clean, new fuel. Clean air cleaner. Cleaned and lubed linkages, set to length according to manual. New governor and control rod springs, all in correct locations. Very little (almost none) play in governor rockshaft, no elongation in holes, fly weights free, thrust bushing and bearing look almost new. Adjusted bumper spring and high stop to “balanced”. Checked timing once again. Fires on TDC, firing order correct. Idles fine, high RPM idle good, but hard to set sometimes.
Still Bucks like crazy going uphill, with only a little load.
Ideas? Coil? It’s original I think.
Calling it quits for today. Thanks

 

[Aasafetypilot]

And forgot to add new carb, cleaned all screens. Set needles by ear, but wondering what would be a good setting (turns) others have used.

 

[Mrfred54]

How much gas is in the tank? Going up a hill it maybe running out of gas?

 

[Janicholson]

And forgot to add new carb, cleaned all screens. Set needles by ear, but wondering what would be a good setting (turns) others have used.

Finding the cause is the key. A broken ignition wire or one that intermittently grounds or shorts to another wire can do it only when going up hill. If it pulls hard and can work to full engine capacity (be well into the governor) on flat ground, then suspect wiring! Fuel tank fill , as mentioned is very real as well. Does using the choke in small increments help! Jim

 

[used red MN]

And forgot to add new carb, cleaned all screens. Set needles by ear, but wondering what would be a good setting (turns) others have used.

But does the fuel flow as per my questions/explanations in reply 5? Particularly out of the carb drain plug. This may be a situation for a timed quantity fuel delivery test. Don’t want to write that out tonight. Also a “new” carb “does not good make” (per Yoda) Some budget replacement carbs have been found to have incorrectly drilled passages. Right or wrong initial settings I would use would be 3 out from lightly seated on the main jet and 3/4 turn out on the idle jet, we’ll see what others say.

 

[DaveBN]

Grasping at straws here, there is a small pin in the end of the governor housing. That pin is 3/16 inch or so and is hard to see if the governor housing is not very clean. That pin sets the lash on the end of the governor rod and can be driven inward to make up for wear. There is a spring on the end of that governor rod. I'm not exactly sure how to make this adjustment but you should at least be aware of it.
Dave.

 

[Aasafetypilot]

Dave - not sure of the pin you’re talking about - there is one on the bottom of the governor cover that internally rides between the fork in the rock shaft. There is very little wear on mine, and seems to be functioning as it should.
To used red MN.. the fuel feed to the carb is good - steady stream with no hiccups. I reset the carb to your recommendations… no change to the lack of power under load.
To all - I feel it may be a timing issue. Am I correct in assuming that if it runs well at idle, and even higher rpm, that the timing is correct? At TDC (compression) the rotor points to #1 terminal on the cap. Rotating the mag with engine running at mid rpm I notice NO change in engine sound or rpm. Is this normal?
Thanks
Jim

 

[Aasafetypilot]

And to Jim… using the choke does seem to help sometimes, and not others…