1650 Keeps Frying Coils

vr4Legacy · #1 04-10-2018, 11:16 AM

I picked up a 1650 last fall and have slowly been bringing it back. Had to have spark plug threads repaired. Replaced the head gasket, new points and condensor, retimed and got it firing up really well.

However, I have fried 2 coils on it. Both after less than an hour of run time. I tested them using this as reference http://www.onlycubcadets.net/forum/showthread.php?t=11

Each time I get no continuity between + and -. At first I assumed it was just a bad or old coil, as it was the one on the tractor. Perhaps it didn't have a resistor. I ordered a new one with a resistor, listing specifically stated it had a resistor and was for Kohler K motors. Put it on and it fired right up and ran great. Was running the motor to get the carb set and check everything out, and after about 20 mins, it just shut off. Tested coil, and wham, no continuity between + and -.

I put another coil on and it fired right back up. I am hesitant to run it very long because I'm afraid I'll burn it up too.

What could cause this? Just bad luck with coils?

I have found that the + wire to the coil and the wire to the middle terminal of the rectifier both have quick splices on them, so the PO has tinkered with the wiring. I plan on splicing and soldering those, but I can't imagine that is causing an issue. The brake safety is also jumped with a wire. I'll double check and make sure it's a good and clean too.

The points wire was also bypassed with a 12 ga wire just hanging around the motor when I got it, I replaced it with a 14ga wire (looks like what is on my 1200) and new ends, rerouted it back the same way it is on my 1200. I can't imagine that's too small of a wire for that. But perhaps.

Anything else specifically I should check for or test? I really don't want to ruin another coil.

J-Mech · #2 04-10-2018, 11:36 AM

Few questions:

*How do you "bypass" a points wire? (As you stated was done before you repaired it.)
*What voltage do you have at the battery when the engine is running? It would be nice to know a voltage at both an idle, and WOT.
*Where is the condenser mounted? (And) Is it hooked to the same terminal on the coil as the points wire?
*What brand and part number is the coil you are using?

vr4Legacy · #3 04-10-2018, 12:00 PM

Quote:

Originally Posted by J-Mech

Few questions:

*How do you "bypass" a points wire? (As you stated was done before you repaired it.)

Poor terminology on my part, the points wire was replaced with a wire just running around the engine to the points. It was red 12 ga stranded wire. I wanted to replace it properly, with black wire. So I used 14ga, which is what appears to be on my 1200. But, the first one went out before I replaced it.

Quote:

*What voltage do you have at the battery when the engine is running? It would be nice to know a voltage at both an idle, and WOT.

Have not checked, but can probably do so tonight, if not I'll check tomorrow. Having said that, it was dead when it died last time, wouldn't even engage solenoid. Recharged and it wouldn't fire up, that's when I checked the coil.

Quote:

*Where is the condenser mounted? (And) Is it hooked to the same terminal on the coil as the points wire?

Yes, on negative side, bolted on top bolt of coil mount.

Quote:

*What brand and part number is the coil you are using?

This one
https://www.ebay.com/itm/Ignition-Co...72.m2749.l2649

Brand on box is BBT. I can get the P/N tonight, I believe I kept the box. First coil has no markings other than +/- on top posts.

ironman · #4 04-10-2018, 12:06 PM

Quote:

Originally Posted by vr4Legacy

I have found that the + wire to the coil and the wire to the middle terminal of the rectifier both have quick splices on them, so the PO has tinkered with the wiring. I plan on splicing and soldering those, but I can't imagine that is causing an issue. The brake safety is also jumped with a wire. I'll double check and make sure it's a good and clean too.

I would pull the plug off of the key switch and use this drawing to verify that all wires go from it to the connections that they are supposed to and are not shorted or grounded.

J-Mech · #5 04-10-2018, 12:24 PM

The only things that can cause a coil to burn up are:
*Incorrect internal coil OHM rating.
*No resistor (internal or external).
*Overcharging (Related to internal OHM rating, and point dwell. Dwell is basically set on this motor when timed properly.)
*AC voltage leak from the alternator. Or feeding too many volts to the coil. (Failed voltage regulator)

I would be looking for these things. Could also just be bad luck, bad coils. The one you bought appears correct.

vr4Legacy · #6 04-10-2018, 01:08 PM

Quote:

Originally Posted by J-Mech

The only things that can cause a coil to burn up are:
*Incorrect internal coil OHM rating.
*No resistor (internal or external).
*Overcharging (Related to internal OHM rating, and point dwell. Dwell is basically set on this motor when timed properly.)
*AC voltage leak from the alternator. Or feeding too many volts to the coil. (Failed voltage regulator)

I would be looking for these things. Could also just be bad luck, bad coils. The one you bought appears correct.

The coil read ~4 ohms when I got it.

Any way I can test the regulator? The middle terminal (DC) was loose and sparked a couple times before I caught it. I replaced and insulated the connector. Tractor ran fine for a while after that, but I suppose those sparks could have weakened the coil.

J-Mech · #7 04-10-2018, 01:13 PM

Quote:

Originally Posted by vr4Legacy

The coil read 3 ohms when I got it.

Any way I can test the regulator? The middle terminal (DC) was loose and sparked a couple times before I caught it. I replaced and insulated the connector. Tractor ran fine for a while after that, but I suppose those sparks could have weakened the coil.

Yes, do as I asked and report DC battery voltage at idle and WOT. I don't want you to burn up another coil getting that info, so you can save the WOT reading for later.

Testing for an AC voltage leak is complicated, and unless it's a very large leak, you may not find it anyway. Usually it fries the points and condenser before the coil.

Those sparks were caused by a poor connection. It didn't hurt your coil.

dodge trucker · #8 04-10-2018, 01:15 PM

As I remember with a points system, you need a coil with around 5 ohms or else you need to wire in a resistor to the+ side. 3 ohms would be more suited to electronic ignition.
Just went through that when I had to replace the coil on an off branded tractor with a KT 19 on it which calls for the exact same points and condenser as a cast iron single cylinder Kohler.

vr4Legacy · #9 04-10-2018, 01:15 PM

Quote:

Originally Posted by J-Mech

Yes, do as I asked and report DC battery voltage at idle and WOT. I don't want you to burn up another coil getting that info, so you can save the WOT reading for later.

Will do. Hopefully I'll get to it tonight, if not def tomorrow.

Thanks!

vr4Legacy · #10 04-10-2018, 01:16 PM

Quote:

Originally Posted by dodge trucker

As I remember with a points system, you need a coil with around 5 ohms or else you need to wire in a resistor to the+ side. 3 ohms would be more suited to electronic ignition.

It was closer to 4 IIRC. The reference diagram says 4-8 +/- 10%. So I think I'm good there.