Farmall 400 that only runs when starter switch is fully engaged.

[Texasmark]

I'm guessing on this.

When the ignition switch is in the start position the solenoid on the starter sends a full 12 volts to the coil for starting. When the key is in the run position the power to the coil goes through a resistor that lowers the voltage to about 8 volts once the tractor is running. This makes the points last longer.

So turn your key on and check with a test light to see if you have power to the resistor. If you have power there then check for power after the resister. If there is power before the resister but not after then the resister needs to be replaced. If there is no power before the resister then there is a problem in the wiring between the resister and the key.

I had this problem on a 300 that I fixed up. Turned out to be a poor connection in the wire terminal by the key.

If you need to move the tractor you can bypass the ignition switch by running a jumper wire from the positive on the battery to the positive terminal of the coil. The tractor will not turn off until the jumper wire is removed. Do not run the tractor for a long time like this or the coil will get too hot.

Hope this helps.

Just adding to what you said about connections: Might also ensure that the connectors ON/attached to the resistor are good too. Since the resistor is a power dissipating type and gets pretty hot by design, that heat is detrimental to electrical connections and can cause them to open up and cease to conduct current as they age. So a volt/ohm meter would be handy in ensuring that current can flow through that circuit and that voltage is applied and is available through the circuit. So if the resistor turns out to be good then have a look at the wiring attached.

On measuring the resistor, you could use an ohmmeter or just follow the voltage across it when you release the switch from START to ON. Assuming it's purpose is to drop roughly 4 volts (12 to 8) and per the MF service manual coil average current is 5 amperes the resistance would be just under 1 ohm. The resistance of current digital meters (mine anyway) leads when touched together in the OHM function read around 0.4 ohms so the resistor is going to look almost like a short when you read it. Course if it burned open....it is wire wound, then it's a no brainer....infinity.

 

[Dale Barrick]

Well after taking the fuel line apart, I found out that the screen before the carburetor was missing. I removed the drain plug from the bottom of the carb and sprayed cleaner through it. Got some junk out. However, I also noticed all that was coming from the fuel line was a dribble, Since I had already cleaned the fuel line and sediment bowl and bowl screen, I took my compressor and with 10 PSI back blew the fuel line to the gas tank. Well there must have been junk in the tank ahead of the sediment bowl because it poured out after that. My 400 is running again which was just in time as we had a blizzard and we ended up with 7 foot drifts in my yard!
Thanks everyone for your support and guidance!

 

[sunnyside360]

Great to hear you resolved the problem. Reading your post brings back pleasant memories of spending summers at my grand parents large dairy farm in the 50's. They had 7 Farmall M's and H's and got a new Farmall 400 with torque converter around 1955. Thought that 400 was the best tractor ever. There are still lots of those older Farmalls running today. They just seem to never quit.