Super C hard to start after 12 volt conversion

[True Son]

I just converted my Super C to 12 volt. Now it’s hard to start? It always fired right up on 6 volt…

 

[used red MN]

Explain what all you have done in your conversion. Off the top, a 12 volt (approx. 3 ohm primary resistance) does not need an additional resistor in the coil feed circuit.

 

[ss55]

I just converted my Super C to 12 volt. Now it’s hard to start? It always fired right up on 6 volt…

Are the spark plugs actually firing when the starter is cranking, or is the starter spinning over the engine with weak or no spark at the cylinders?

 

[True Son]

Explain what all you have done in your conversion. Off the top, a 12 volt (approx. 3 ohm primary resistance) does not need an additional resistor in the coil feed circuit.

I put on a new 12 volt coil with internal resistor

 

[old]

I put on a new 12 volt coil with internal resistor

No coil has an internal resister they are made for either 6 volts or 12 volts simple as that. You need to check that you have a good blue/white spark at the center wire of the distributor cap and at all 4 plug wires that jump a 1/4 inch gap or more as in simple trouble shooting. You could simply have a bad new coil which sadly happen all to often now days

 

[Janicholson]

Explain what all you have done in your conversion. Off the top, a 12 volt (approx. 3 ohm primary resistance) does not need an additional resistor in the coil feed circuit.

Agree, as we are working toward___ the issue is if you have a resistor in the circuit as well as a 12v (designed) coil. No resistor needed in a true 12v coil. Jim

 

[560Dennis]

Get a piece of paper (white preferably) . Open points , close points on paper. Pull paper out of points . If a black soot comes off , oil or grease has contaminated them .clean points with elec contact cleaner . Retry .

 

[John T]

No coil has an internal resister they are made for either 6 volts or 12 volts simple as that. You need to check that you have a good blue/white spark at the center wire of the distributor cap and at all 4 plug wires that jump a 1/4 inch gap or more as in simple trouble shooting. You could simply have a bad new coil which sadly happen all to often now days

While I NEVER saw a farm tractor coil with an "internal resistor" actually some exist, here's a couple coils with internal resistors (or thermistors or heat compensating resistors)....

Best wishes Happy Memorial Day, Thanks for your service Rich

John T

 

[DaveBN]

Your 12v conversion probably is the cause of bad starting but think real hard about anything else you did or touched. Your problem could be whatever else you did. Regap points, adjust timing, adjust carburetor, new sediment bowel etc.
Dave

 

[Geo-TH,In]

Very few people mention the reason for using a coil and ballast.
My cars in the 60's used both coil and ballast.
The ballast resistor was bypassed when the starter was engaged
because the cranking voltage is always lower than the running voltage when the alternator is working
and lower cranking voltage means a weaker spark.

My old Farmall C uses a very hot magneto. No need worrying about cranking voltage.

The battery on my Converted Jubilee was suffering from an old battery and lower than normal cranking voltage.
The easiest way to bypass the ballast was to use a diode the middle of the

pic,
One end of the diode I connected to the +12 wire going to the starter and the cathode end, the white stripe, going to the coil.

This may be the best reason not to use a 12v coil with internal resistance.
Install a new battery and see if lower cranking voltage is your problem.

 

[old]

While I NEVER saw a farm tractor coil with an "internal resistor" actually some exist, here's a couple coils with internal resistors (or thermistors or heat compensating resistors)....

Best wishes Happy Memorial Day, Thanks for your service Rich

John T

Yes at one time they made them but lets see you buy one today. I've never seen one and if you ask for one you get a funny look from the counter guy since they don't know what your talking about

 

[John T]

Yes at one time they made them but lets see you buy one today. I've never seen one and if you ask for one you get a funny look from the counter guy since they don't know what your talking about

I have actually seen them on a few old cars or old car swap meets, as I noted and the pictures indicate, there are indeed coils that have internal resistors...........

Happy Memorial Day Rich, best wishes

John T

 

[John T]

Very few people mention the reason for using a coil and ballast.
My cars in the 60's used both coil and ballast.
The ballast resistor was bypassed when the starter was engaged
because the cranking voltage is always lower than the running voltage when the alternator is working
and lower cranking voltage means a weaker spark.

My old Farmall C uses a very hot magneto. No need worrying about cranking voltage.

The battery on my Converted Jubilee was suffering from an old battery and lower than normal cranking voltage.
The easiest way to bypass the ballast was to use a diode the middle of the View attachment 72659pic,
One end of the diode I connected to the +12 wire going to the starter and the cathode end, the white stripe, going to the coil.

This may be the best reason not to use a 12v coil with internal resistance.
Install a new battery and see if lower cranking voltage is your problem.

Exactly true very few mention the reason, although myself and a few others have explained it for yearssssss lol Glad to see at least some understand it. What I liked about the ballast resistor by pass system on some old two cylinder Deeres was no diode was even needed. It did improve cold weather starting when battery voltages dropped drastically but that system went by the wayside. Above I posted pictures of some old coils that indeed contained internal resistors but didn’t utilize mechanical switching type of bypass or diodes.

Happy Memorial Day remember the fallen who gave their lives so the rest of us are free

John T

 

[Fritz Maurer]

 

[jdeere562]

I converted a WD to 12 volts. It cranked too fast and was advancing the distributor weights and caused too much timing. It would only pop off when you released the starter button and the engine slowed down. Had to put stronger springs on the weights.

 

[wore out]

View attachment 72719

I would not put much faith in a modern parts catalog description of such parts, the folks that make up those descriptions have likely never even seen what they are writing about, much less have any knowledge or expertise in such parts.

Example, on this very site many rod and main bearings are listed as "OVERSIZED", while the rest of the engine parts world lists them as "UNDERSIZED". If you want to be technical and "old school" about it, "OVERSIZED" rod bearings are for a rod who's "big end" has been reworked to an "OVERSIZE".

Cut one of those coils open and show me a discrete resistor and I'll believe!

 

[HFJ]

I converted a WD to 12 volts. It cranked too fast and was advancing the distributor weights and caused too much timing. It would only pop off when you released the starter button and the engine slowed down. Had to put stronger springs on the weights.

strange. i have a WD that a PO converted to 12 volts. it starts easy every time. now i wonder if he replaced the springs too.

 

[jdeere562]

strange. i have a WD that a PO converted to 12 volts. it starts easy every time. now i wonder if he replaced the springs too.

No idea, just my experience. Have only done that one. I just threw that out as something to look at as a possible problem.

 

[Janicholson]

I converted a WD to 12 volts. It cranked too fast and was advancing the distributor weights and caused too much timing. It would only pop off when you released the starter button and the engine slowed down. Had to put stronger springs on the weights.

That issue could also be a starting voltage issue. If it is cranking fast, the engine usually will spin past advanced spark. If it is actually kicking back against rotation then sure. Experience based opinion, Jim

 

[John T]

I would not put much faith in a modern parts catalog description of such parts, the folks that make up those descriptions have likely never even seen what they are writing about, much less have any knowledge or expertise in such parts.

Example, on this very site many rod and main bearings are listed as "OVERSIZED", while the rest of the engine parts world lists them as "UNDERSIZED". If you want to be technical and "old school" about it, "OVERSIZED" rod bearings are for a rod who's "big end" has been reworked to an "OVERSIZE".

Cut one of those coils open and show me a discrete resistor and I'll believe!

X2. I have told people the same on here for yearssss. While a few old mostly car coils did indeed have discrete stand alone resistors in the bottom of the can (see my pics above) I’ve never seen any later model tractor or automotive coils that even though labeled internal resistor actually had a resistor inside. Instead the necessary resistance was made up by the coils of wire and its own linear resistance, NOT any actual resistor tucked away hidden inside the can regardless what they are called. That’s my story n Ima stickin to it. As I explained to Rich above it’s not true that NO coils have internal resistors as he stated . However the modern ones pictured above regardless of the labeling I agree with you do NOT have discrete stand alone resistors inside them.

John T