WTB: Coil that matches a 25D Distributor [Woodinville, WA, USA]

Hi all,

I have an issue with an intermittent "misfire" on my 1978 Roadster. I fitted a 25D distributor last year so I would imagine that the coil would have to be 25D appropriate. I dont want to spend a bunch of money on a new coil as Im not sure thats even the issue. I switched out everything (ignition wise) except for the coil.

Thanks all, John

John
Did you possibly install an Ignitor in your distributor?
Could possibly be a cause?

I would suspect a condenser before a coil given its a misfire. On the other hand....your stock unit coil would be ballasted and you need an unbalasted unit. Lucas 101 or Sports 105. You are only getting half the juice if you installed the 25 without the proper coil....

Either will be quite heated if they are failing.

New coils aren't expensive and if you get a used unit you probably won't know for sure that it really is good...

no "25D coil" exists. Your (1978) car's wiring harness has a built in resistor so your coil for your car should actually NOT be the same as used on cars that used a 25D since they did not have this resistor.

Interesting. When Iremoved the stock Lucas electronic-ignition type distributor. I just replaced it with a 25d, ran power to the 25D from the coil and have driven it like that for over a year.

I "think" what you are saying is that I got lucky in my ignorance and I actually need a stock coil from a 1978 setup - that had the Lucas electronic ignition?

Thanks all!

John - you may be onto something here. I suggest a new thread in the other forum, and provide and indication of:

- points or electronic ignition?
- 1.5 ohm or 3 ohm coil? (you can probably search for how to tell....)
- how exactly it's wired up (look through the wiring diagrams at Advanced Autowire .com to compare the later '78 diagram with an earlier 25D car, say from '69 or '70...)

Rick Astley's book on MGB Electrical Systems would really help you right about now....

Bob

John almost all if not all MGBs have the resister that Mac refers...it steps voltage down for the electronics. What you need to do I suggest is get a coil for a pre 1975 and be sure you delete the resister. This isn't my forte per se but since the beginning of time...well with 12v cars, the coil starts on 12v and runs on 6v to preserve the points. The electronic ignitions have no points thus the resister is in place and lowers current flow.

Its not so much lucky as having a dizzy operating with an incorrect coil.

In your case you have only partially swapped out the coil/dizzy combo. Newer style dizzy replaced with older style dizzy. Coil for the newer left in place and should then and now be replaced with the corresponding correct coil.

Thanks again all.

So I need to:

1. Get a hold of a coil suitable for a pre-1975 car
2. Remove the "resisitor" that should be in place on my 1978 car - anybody have a pic/location of this resistor?

What symptoms would I see if I ran a 25D, 1978 Coil and left the resistor in place - as I have dont for quite awhile now?

Thanks for your patience :)

I could be wrong, but I think that the ballast resistor on the later cars consists of some wiring that runs forward to the left headlamp area and terminates.