4020 lp spark

Went to start 4020 lp today and wouldn't
start. Checked the spark. It had spark but
was very weak. Checked the points everything
looked good. Took the coil off and it says
6v. The tractor has had a 12 volt
conversion. I want to do a ignition tune up
on the old girl. But should I replace the
coil with a 12volt coil with an internal
resistor or should I put another 6 volt back
on? Any help would be greatly appreciated.

Is the ballast resistor still there and functional ?

I would check the condenser first for a weak spark.

Take cap off, open and close points with plastic screwdriver, a lot of sparking across points can indicate weak condenser.

That tractor would of came new 12 volt. It was not converted.

There is not a ballast. The wire comes off
the solenoid on the starter to the coil and
into the distributor. The tractor has one
single 12 volt battery and is running a one
wire Delco alt. I've been using this tractor
for awhile and has run good. I looked up the
part number for that coil and it looks like
it can be used for 6 and 12 volt but should
it have a ballast.

That Vintage Deere had resistor built into key switch IIRC.

If you're using a 6 volt coil UNBALALSTED on a 12 volt tractor the points will burn and carbon prematurely resulting in a weak spark plus the coil can overheat and be damaged. That tractor was always 12 volts and if it really ?? had a 6 volt coil it would need an external series voltage dropping (12 down to 6) discrete ballast resistor or some sort of a resistive wire or a thermistor type wire link (on switch or elsewhere) with resistance that increases with temperature. If it had a temperature compensated resistive wire link (on switch or elsewhere) it starts out at low resistance for good cold starting but when warm its resistance increases and if enough you could use a 6 volt coil on a 12 volt tractor.

Points that are burned or pitted or oxidized or not gapped correct is one cause of a weak spark followed by a bad or weak condenser. If the coil overheats it can go bad.

John T

THEN LATER THEY HAD A RESISTER WIRE , ALL 6 VOLT COILS .

The free parts book on the JD web solves many mysteries . http://m.jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt

Your post reminded me of something funny that happened to me. I was working on a Deere 1010 that had intermittent ignition problems. Burned up distributor caps often and only ran decent with the timing way off (according to the timing light). I ran it that way for a year. Hard starting, ran hot, etc. Ends up it had a distributor in it from a Deere 4020. So it had a 6 lobe points cam but a four-cylinder cap on it. Took me quite awhile to discover the problem. I then took a four-cylinder distributor from a Case tractor, put it on the 1010, and it ran like a new machine.

I stopped at a farm store today and got a condenser. I noticed alot of spark coming from points and with cap on can hear it arching. I will be stopping at deere tomorrow to get parts. Funny thing is it ran fine two days ago. Thanks for everyone's input so far hopefully I can get it going tomorrow.

Below you stated "I looked up the part number for that coil and it looks like it can be used for 6 and 12 volt but should it have a ballast. "

Sure a 6 volt coil can be used on EITHER a 6 or 12 volt tractor HOWEVER as you indicated IT NEEDS A VOLTAGE DROPPING (12 down to 6) ballast if used on a 12 volt tractor.

When you state its wired off the starter solenoid I WONDER IF IT GOT RE WIRED INCORRCT AT SOME TIME??? I have seen ballast resistance wired 1) On the ignition switch 2) A resistive or thermistor (temperature compensated resistance) wire link device between switch and coil 3) Stand alone discrete bathtub style ballast resistor between switch and coil.

If its a 6 volt cool and is MIS wired such that there's no ballast on the switch or resistive wire link or thermistor wire after switch or a stand alone ballast resistor THE COIL CAN OVERHEAT AND THE POINTS BURN PREMATURE AND CAUSE A WEAK SPARK

TO SEE IF ITS BALALSTED AND MEASURE COIL INPUT VOLTAGE

Stick a volt meter on the coils input,,,,,,,,turn ignition on,,,,,,,,,with points closed see if its around 5 to 7 volts or battery voltage????????????? IF 12 VOLTS ON A 6 VOLT COIL UNBALLASTED the coil runs hot and points will burn and you get a weak spark HOWEVER IF ITS 5 TO 7 VOLTS ON A 6 VOLT COIL THATS LIKELY OKAY

Since its a 6 volt coil and a 12 volt tractor YOU NEED A BALLAST be it on the switch or a resistive wire link or thermistor temp compensated wire device AND IF ITS WIRED SO YOU DONT HAVE THAT points will burn soon and burned points causes a weak spark.

YOU HAVE TO MEASURE COIL INPUT VOLTAGE WITH IGN ON AND POINTS CLOSED TO SEE IF ITS BALLASTED!!!!!!!!!!!!!!!!!!!!

John T