Missing at full temp

[jbowlby]

Im trying to diagnose why at full temp my 73 Midget 1275 is missing. New petronix and coil, freshly rebuilt carbs. no vacuum leaks.
I have noticed the coil is HOT to the touch after running. Could this be a sign of a faulty coil. I was under the impression a coil would either work or not.

Thanks!

 

[Jim_Gruber]

You might have a coil that requires a ballast resitor. These types use a higher voltage to start and then run at a lower voltage. I had that issue with a Mercruiser and went through 5 coils before I found out from sources other than the extras from the movie Deliverance that were holding my boat captive. Idiots, idiots, I was surrounded by idiots. And while the coil was working boat ran like a scalded cat. Then progressed into missing, missing, missiung runing worse and worse and finally quit.

And yes if coil is runing at too high a voltage it will get extremely hot and burn up.

 

[Trevor Jessie]

I do not think a coil would cause a miss. It could be a bad rotor button and/or cap ... or plug wires.

I replaced my rotor button and cap with a unit from Jeff of advanceddistributors and my idle smoothed out quite a bit.

 

[GrahamP]

I had that problem on my frogeye and it did turn out to be the coil!
Graham.

 

[Trevor Jessie]

OK, I'm apparently wrong.

The thing to do would be to check the resistance of both the low and high tension of the coil while it is hot and see if there is a short.

 

[Trevor Jessie]

BTW, Doug Lawson wrote this very nice article that might help even though you are using pertonix:
https://home.mindspring.com/~purlawson/files/LucasPointsIgnitions.pdf

 

[jbowlby]

Wish me luck, im heading to the garage with a large glass of ice water. I will switch the coil out with the old one. I dont know about you guy's but it's a tempid 97 here in Memphis today!

 

[jbowlby]

It's fixed! While I was switching out the coil I noticed a small black line in the coil wire. It had arched out and was causing the misfireing at full temp.

I guess a good rule to follow is when your stumped don't forget to check the obvious! I will add that the wire set was less than 1 year old and had less than 500 miles on them.

Thanks to everyone for your help!

 

[jlaird]

Well done. Always nice to find a cheep fix.

May I suggest that when you have a miss or interment miss you check the engine running in the dark.

 

[mrsprite]

Same thing happened on my nearly new set of plug wires. I had a very small rip in the boot and it arced and sparked (and missed) like crazy......drove me nuts figuring it out because how could a 3 month old set of $80 plug wires possibly be bad?

Anyway, glad you found the problem and that it's an easy fix.

 

[tweety]

so it was missing at IDLE when warm? Did you even try to drive it? If so what did it do.

Congrats BTW, there's nothing better than a simple fix for a problem that caused much mental agony

 

[Jim_Gruber]

With these cars it's usually something simple. We always go for the catostropic solution when often just plain old wear and tear or a loose connection.