weak spark on a ford 4000 forklift

[Charlie M]

I've asked a couple of other questions previously on this project if the title seems familiar. We have a forklift based on a Ford 4000 4 cylinder tractor at our rail road museum I am trying to get running and its turning out to be quite different from what I know about my Farmall tractors. The machine was running fine until one day it wouldn't start. I volunteered to help get it running and the first thing I did was check for spark and it was good. Turned out the original problem was junk hanging up the float needle valve that was allowing gas to flood out the carb and then flood out the engine. I fixed that. Getting back to the spark issue the first thing I found was the resistor used for the 12 volt conversion was between the coil and the distributor. One of our attempts to check the voltage must have happened when the points were closed and the resistor began to smoke badly and since then we have had a weak spark. When I look up resistors for 12 volt conversions on this tractor there are two shown - one has a 2 ohm resistance which I use on my Farmalls and the other has a less than 1 ohm resistance which I don't under stand when it would be used at all. Can someone tell me what should be used on this tractor. The coil on the tractor says 12 volts with resistance or 6 volts. I'm thinking the fix to the machine without making it a 6 month project is to replace the points and condenser but I don't want to put on new parts and use the wrong resistor. I also don't want to spring for a different coil and remove the resistor either unless I have a better idea on what's happening. This has been a good project for me to further realize why I have only Farmall tractors because that is what I have learned to work on over the years.

 

[Jim.ME]

I've asked a couple of other questions previously on this project if the title seems familiar. We have a forklift based on a Ford 4000 4 cylinder tractor at our rail road museum I am trying to get running and its turning out to be quite different from what I know about my Farmall tractors. The machine was running fine until one day it wouldn't start. I volunteered to help get it running and the first thing I did was check for spark and it was good. Turned out the original problem was junk hanging up the float needle valve that was allowing gas to flood out the carb and then flood out the engine. I fixed that. Getting back to the spark issue the first thing I found was the resistor used for the 12 volt conversion was between the coil and the distributor. One of our attempts to check the voltage must have happened when the points were closed and the resistor began to smoke badly and since then we have had a weak spark. When I look up resistors for 12 volt conversions on this tractor there are two shown - one has a 2 ohm resistance which I use on my Farmalls and the other has a less than 1 ohm resistance which I don't under stand when it would be used at all. Can someone tell me what should be used on this tractor. The coil on the tractor says 12 volts with resistance or 6 volts. I'm thinking the fix to the machine without making it a 6 month project is to replace the points and condenser but I don't want to put on new parts and use the wrong resistor. I also don't want to spring for a different coil and remove the resistor either unless I have a better idea on what's happening. This has been a good project for me to further realize why I have only Farmall tractors because that is what I have learned to work on over the years.

If you were testing and made the resistor smoke badly, the points would have been closed, as you posted. You also posted that happening was the start of the weak spark issue. You likely burnt the points at that time, and they now need replacing now for that reason. Start there.

To determine which resistor is needed to go with the existing coil, you need you first need the resistance of the coil you have. The total resistance of the two should be 3 ohms (+) to limit current to 4 amps at the points. It is possible there is a resistor wire in the circuit, see what voltage it shows reaching the coil when it is running. With the resistor after the coil there should be system voltage at the coil input terminal. If there is less than system voltage that could be the cause of the weak spark.

If it has a 4-post Ford type solenoid with the "I" terminal (that has power when cranking) move the resistor to be in the switch side wire to the coil. Then run a wire from the "I" terminal of the solenoid to the coil input terminal where the wire from the resistor is now connected. That will provide a resistor bypass providing full voltage for a better spark during cranking.

The same points and condenser will work on both 6 and 12 volts. I would check to see that there was 12-volts (system voltage) to the coil all the time then put a true 12 volt coil on it and do away with the resistor. A true 12-volt coil will often be labeled "12 volt no external resistor required", or similar. Standard Motor Products UC15 (or the optional UC15T), and Echlin 1C14 are a couple, if you decide to go that route.

 

[John T]

Mornin Charlie, let me give you a few basics regarding old tractor point
coil ignitions.

1) In order that points dont burn prematurely current is limited to 4 or so amps which means a) On a 12 Volt circuit the total (coil + any ballast) LV primary resistance is 3 Ohms as 12/3 = 4 Amps b) On a 6 volt tractor the total LV resistance is 1.5 ohms as 6/1.5 = 4 Amps.

2) If you wanted a 50/50 voltage divider and needed 6 volts on a 6 volt coil on a 12 volt tractor, COIL RESISTANCE IS SAME AS BALLAST RESISTANCE such as for example each = 1.5 Ohms.

3) On a 12 volt tractor you can use EITHER a) A 6 volt coil PLUS a ballast that drops 6 volts orrrrrrrrrrrrr b) A full true 12 volt coil no ballast required

4) Points and condensor are current devices and have a voltage withstand rating MUCH ABOVE 6 or 12 volts so same can be used on EITHER a 6 or 12 volt system.

5) A full true 12 volt rated coil may be labeled 12 Volts or 12 Volts NOT for use with ballast and will have around 3 ohms (seen 2.5 to 4) LV primary resistance

6) TYPICAL (not all) 6 volt coils have around 1.5 to 2 ohms resistance while TYPICAL (not all) 12 volt coils have around 3 ohms resistance (seen them 2.5 to almost 4)

7) Typically old tractor 12 volt coils DO NOT have any discrete ballast resistor hidden tucked away inside the can but derive the 3 ohms from the LV primary winding resistance

SOOOOOOOOOOOOOO on a 12 volt tractor insure TOTAL (coil + any ballast) LV primary resistance is around 3 ohms (12/3 = 4)....That can be done AGAIN either with a 12 volt 3 or so ohm coil no ballast required orrrrrrrrrrrrrrrr a 6 volt coil PLUS a voltage dropping ballast. A full true 12 volt coil is easy and simple with less connections to worry about HOWEVER it lacks the advantage of cold weather improved starting in cases where a 6 volt coil is used and the ballast is by passed when cranking

I hope this helps and others can add to this

John T

 

[showcrop]

I've asked a couple of other questions previously on this project if the title seems familiar. We have a forklift based on a Ford 4000 4 cylinder tractor at our rail road museum I am trying to get running and its turning out to be quite different from what I know about my Farmall tractors. The machine was running fine until one day it wouldn't start. I volunteered to help get it running and the first thing I did was check for spark and it was good. Turned out the original problem was junk hanging up the float needle valve that was allowing gas to flood out the carb and then flood out the engine. I fixed that. Getting back to the spark issue the first thing I found was the resistor used for the 12 volt conversion was between the coil and the distributor. One of our attempts to check the voltage must have happened when the points were closed and the resistor began to smoke badly and since then we have had a weak spark. When I look up resistors for 12 volt conversions on this tractor there are two shown - one has a 2 ohm resistance which I use on my Farmalls and the other has a less than 1 ohm resistance which I don't under stand when it would be used at all. Can someone tell me what should be used on this tractor. The coil on the tractor says 12 volts with resistance or 6 volts. I'm thinking the fix to the machine without making it a 6 month project is to replace the points and condenser but I don't want to put on new parts and use the wrong resistor. I also don't want to spring for a different coil and remove the resistor either unless I have a better idea on what's happening. This has been a good project for me to further realize why I have only Farmall tractors because that is what I have learned to work on over the years.

I wonder how you determined that it was flooded.

 

[Charlie M]

I wonder how you determined that it was flooded.

Knew the carb was flooded when I removed the air breather hose and gas ran out and wouldn't stop. Knew the engine was flooded when I pulled the plugs and they were wet with gas.