1975 Farmall 140 - Only Fires When I Let off of Starter

[RTR]

Got a 1975 "key start" Farmall 140 tractor, and I just completed a fresh tune up today with new points, plugs, rotor, and condensor. Wires & cap looked good, so left them alone. Carburetor has been professionally rebuilt.

This tractor has 150 psi on all 4 cylinders, yet it starts hard....even after the tune up. I have noticed that when starting it, you can hold down on the key and turn the engine over from "now til next month", and it will not
'fire' or 'crank up' Until you let go of the key/stop turning over on the starter.

I have never seen a tractor do this....what is the problem!? I want it to start up on the first turn or two without havin to let go of the key.
 

[ShaggyM]

My Super C use to do the same thing. It had a resistor before the coil. But the Coil had a built in resistor and with the draw from the starter it didn't had enough juice to fire.
I just took out the external resistor and it had been fine ever since
 

[David G]

Voltage is low starving the coil when it is cranking.
 

[El Toro]

You may have a defective ballast resistor. I would check the battery voltage while cranking to see how low your voltage is. Check the specific gravity in each cell using a hydrometer. Should see 1.280 on a fully charged battery. Hal
 

[fixerupper]

Could be the shunt wire that bypasses the resistor when you hit the starter is broken or loose. Run a jumper wire from the positive post on the battery to the positive (+) terminal on the coil and then hit the starter. If it fires right off you've found the reason for the hard starting problem. Then you'll have to start tracing the wiring from the coil back to the ignition switch until you find it. Could be a bad switch or a wire that's vibrated off of the switch. Jim
 

[RTR]

I don't see a resistor anywhere on this tractor. The coil isn't readable as it is rusty and dirty. I don't know if it's a coil with internal resistor or not. The wire goes straight from Key Switch to Coil (+), then wire from Coil (-) to Distributor.
 

[Huskers86]

[pete 23]

Question, is it 12 volts originally. Reason I ask
is that if it is , no doubt it will have a
solenoid on starter or starter relay with a bypass
terminal on it. This is to supply full battery
voltage to ign coil when cranking. There will be a
two small wire terminal, and one wire goes
directly to coil, other is a resistor wire coming
from ign switch. Hard to tell by looking at the
wire. You can put a volt meter on that terminal
and at input side of coil to check your voltage.
Points have to be closed so they are completing a
circuit. If you do indeed have what I describe you
will read about half of battery voltage. Now,
while cranking, the voltage at that terminal
should be same as cranking voltage of battery. May
just be a bad relay but could be other wires or
connections. At any rate, you are getting very
low voltage to coil during cranking, thus poor
spark for starting. You can check resistance of
coil with ohm-meter. If it is a true 12 volt coil
the readings between the two primary terminals
will be about 3 or 4 ohms. If six volt, which it
should be ,it will be l.5 to 2.5 ohms. So many
guys look for visible resistors, when later model
tractors incorporated it in the wire and is
invisible. But if it has two wires leading off one
terminal of solenoid or magnetic switch, it is in
harness.
 

[old]

No such thing as a coil with internal resister they are just made for 12 volts simple as that. That said try this. Hot wire the thing ans then try to start it. If it starts up like it should it most likely has a bypass set up so more volts go to the coil. If it does have a ballast resister it can be hidden where you may not see it also so the by pass could be your problem
 

[Janicholson]

I will add that if the tractor cranks slowly, it is having two issues at the same time. One is that the slow cranking is possibly a result of long modest battery cables. Putting #2ga. battery cables will perk up the voltage going to the starter. Low voltage at the starter will feed low voltage to the ignition. Making it crank well also makes the voltage higher.
From looking at the carter and Gruenwald wiring diagrams, there appears to be no bypass.
If fatter cables doesn't fix it, the following will"
One pretty simple way to get the full voltage to the coil on start is to put a 12v coil on it that uses an external resistor. Then add a ballast resistor (1965 chevy ceramic ignition resistor with a ceramic design) Put the ignition (black from key) wire on one terminal of the resistor, and hook the other to the negative terminal of the coil. Next use a #12 wire from the starter side of the big starter switch (hot only when the starter is turning) take this wire to the ballast resistor and put a 4 amp diode on the end so that the electricity can flow to the ignition, but not back to the starter. Connect the other end of the diode to the coil side of the new ballast resistor. You have now added an isolated ignition bypass. If the diode is in backwards, it will melt the ballast resistor. Jim
 

[RTR]

How would I know if my coil requires an external resistor? It isn't even marked 6 or 12 volts.

I somewhat follow your wiring schematic. Is there any way you could provide me with a drawing explaining it? That would be MUCH easier to see and understand what you are talking about.

THANKS!
 

[504]

Bad switch.
 

[old]

If you do not know basic electronics it is very hard to explain a wiring diagram. Since the keyboard does not have the pictures/keys needed to show you what each symbol is that makes it even harder.
 

[Janicholson]

Here is the diagram. It will allow better supply of starting voltage. 1N5408 diode. Jim

 

[gene bender]

Sounds like bad sw or wiring. You need a voltmeter to see if you are getting batt voltage when cranking the engine. Must not or it would start.Just get a meter and some jumper leads so you can get some readings and you will find the problem.