external, internal resistor for coil with EI

[Fstued]

I have a new rebuilt engine ran great for a while then it stopped and won't start
I chased the power since there was no spark. The coil says on it use with external resistor. I don't see a resistor. I assume there are internal resistors also. Anyway after much diagnosis. It looks like the problem might be the electronic ignition. Would not having the external resistor cause the EI distributor to burn out and not produce spark. When bypassing the distributor I get spark at the coil. That says to me the problem lies in the EI . If I have a resistor where would I find it?

Thanks

[joe_db]

I have a new rebuilt engine ran great for a while then it stopped and won't start
I chased the power since there was no spark. The coil says on it use with external resistor. I don't see a resistor. I assume there are internal resistors also. Anyway after much diagnosis. It looks like the problem might be the electronic ignition. Would not having the external resistor cause the EI distributor to burn out and not produce spark. When bypassing the distributor I get spark at the coil. That says to me the problem lies in the EI . If I have a resistor where would I find it?

Thanks

Using a coil that needs a resistor and not having one will burn out some of the commonly used EI units. Can you send a description of what you see under the distributor cap?

[JOHN COOKSON]

I have a new rebuilt engine ran great for a while then it stopped and won't start
The coil says on it use with external resistor. I don't see a resistor.
Thanks

Take a resistance reading between coil + and coil - and see what is really going on.
There must have some resistance somewhere between coil + and ground or it would have turned into a momentary arc welder. The engine ran with the coil so there had to be some resistance to ground.

TRUE GRIT

[joe_db]

I am sure the coil has SOME, just not enough. It would burn out eventually even with points, but it can do EI in pretty fast.

[ndutton]

It's pretty clear you're headed for a replacement EI AND a proper coil. If you want to fine tune the coil resistance, use the calculator found here or as a generic approach make sure your coil + supplemental resistor (if necessary) add up to 4Ω minimum. Be careful with this, resistance can be overdone too.

I wouldn't dally around with this or take a piecemeal approach. A reliable ignition system is the goal and these replacements will achieve it.

[joe_db]

+1
A lot of experiments went into the Moyer coil - just buy it and it will work with points or EI

[ndutton]

We continue to recommend measuring the internal resistance of any coil, MMI coils included, to apply the formula accurately. Vendors change over the years so it's best to be vigilant and confirm these things ourselves.

[Ken Rockwell]

I'd get two......if I was in a boat, and my engine was just rebuilt, and my coil just fried.