farmall M

[geezer in mo]

carb or ignition problem? have a 48 M, rebuilt the carb. She will start and run but not the way I would like. It has a 12 volt conversion on the distrib. seem like I have better spark with the resistor in back wards but won"t shut of with the switch that way. any one have any ideas?? thanks G

 

[Captndan]

Not sure what a 12v conversion at the distributor means. If this is a true 12v conversion with a 12v battery the resistor is not needed. If it has a 6v battery it needs a 6v coil. The resistor is used to step down 12v to 6v if a 6v coil is used on a 12v conversion. Hope this makes sense.

 

[geezer in mo]

yes it still has the 6 volt coil,so it is stepped down , my question is , it appears to have better spark with the resister backwards so it will not shut off with the switch.I'm thinking about going to a 12 v coil.Would that be a better chose?

 

[Anonymous-0]

Your question makes no sense to me. A resistor has no backward or forward it reduces 12 volts from the switch to the coil.

 

[teddy52food]

What do you mean by resistor backwards?

 

[Shawn in PA]

Did you check the voltage? You said it appears to have a better spark. Put in a 12 volt internally ballasted coil. Thats what i have on mine. Hasn"t given me any trouble.

 

[geezer in mo]

perhaps I'm not calling it in the right term. I have fuse link with what appears to be a resistor of some sort, instead of a fuse. If I install this piece in one way the tractor will not shut off. if i turn it around it will..this runs from a ceramic block into the coil! my understanding is that this conversion was done about 15-20 years ago.and it was done to save from having to buy a 12v coil.the old boy that did it wasn't sure any more what did..sorry that's all the info I have

 

[geezer in mo]

continuing on. this M has had several different ""upgrades"" done back 15/20 years ago.this resistor is in a fuse holder and when installed one way .I can shut the tractor down, installed the opposit way it will not shut off. the guy that did the "conversion" is up there in years now and can only give me a little info.thanks---G

 

[47M]

It sounds like you may have a diode installed instead of a resistor. A diode will conduct electricity in one direction but not the other, they act like one-way valves for electricity flow. Larger diodes are usually black with a while line (indicating the anode end) around one end of the body, with a lead coming out of each end.

 

[Deano]

A resistor doesn't have a right or wrong way to connect. Either end is the same. You likely have a diode which is a directional device. Can you post a picture ( nice close up one ), seeing is helpful

 

[geezer in mo]

deano you are correct! couldn't pull the word out of my brain this morning.Question is, can the diode go bad or loose it's voltage over time? when I start the tractor at first it runs ok but not up to par. then next time hard start w/week spark.also I'm thinking that metering jet may be clogged or just bad . I had a hard time getting it out and back in? Thanks...G

 

[geezer in mo]

thanks!! another right answer. could find the word for it this morning.

 

[47M]

"Question is, can the diode go bad or loose it's voltage over time?"

Diodes usually "short out" where they conduct electricity in both directions, like a piece of wire; or, they open up and don't conduct any electricity at all. Since something changes when you reverse the diode, it seems as though the diode is still good.

But, I don't know why it's installed or what it's purpose is on your tractor. Diodes can be wired into a "generator light" circuit where if all is working correctly (with the generator putting out more voltage than the battery to charge it), no electricity flows through the diode and the "gen" light stays off. If the generator or voltage regulator goes bad and the voltage coming out of them to the battery is lower than the battery voltage, the diode then conducts electricity and turns on the "gen" light to let you know something's not right with the charging circuit.

 

[Janicholson]

I might be helping this situation. The use of a Delco alternator to convert to a 12 volt system is common. There are three connections to it. One from the Big stud terminal to the Amp gauge. One from a small spade terminal #2 that goes to the Big stud terminal. and a small spade #1 that goes to the ignition to start the tractor.
This last wire must have a 10 ohm 10 watt resistor, or a marker sized regular small light bulb, or a diode in series with the wire.
Yours has the diode. The diode is working correctly when it is installed such that the engine does not keep running.
The ceramic resistor is used between the ignition switch and the coil (supposed to be positive) little terminal. The other end of this resistor is connected to the ignition switch directly.
The wire with diode is connected to the resistor on the same end as the ignition switch.
This allows the ignition to supply a exciter source to the alternator through the diode, but prevents the alternator from supplying voltage to the coil when shutting it off.
If the coil gets hot, it may be going out.
If the points and condenser are good, and set to .020", they are good to go. Jim
Bob M diagrams Very Correct one with alternator

 

[teddy52food]

Sounds like a diode , not a resistor.

 

[geezer in mo]

thanks Jim...I believe I'm just going to go ahead and swap out the 6v coil for a 12..sounds like the old 6v one is about done, Could be the original one...G