MG Car Repair: 1976 midget, coil windings, air gap

Question
QUESTION: i have a 1976 midget that i do not want to through alot of money at
my problem lies with no spark
i only have about 7 volts at the coil
where do i start

ANSWER: Hi Greg,
First since you say you only have 7v at the coil, that tells me you have an external ballast resister. There are white wires on the coil (Power side where you got the 7v reading?? correct?) If so, remove the coil wire from the cap while the key is on and you have the 7v at the white wire. Hold the coil wire close to the engine (1/8 inch) or put a spark plug on the end of the wire and lay the plug on a metal part of the engine so you can see a spark. Then while looking at the plug or the 1/8 in. gap, remove the wire/s (White w/black strip) from the other side of the coil. You should see a spark jump. If you do then the coil and wiring is (probably) OK and it becomes an igniter/pick-up problem.
If you didn't get a spark remove the white wires from the coil and with the key on check the voltage of the white wire/s. Should be 12v
disconnected. Check the resistance of the primary coil windings. (+ to -)(wires disconnected) You should see about 1.5 ohm if it is a external resisted coil. Probably 3.5 ohm or so if it is a straight 12v coil. Those figures are off the top of my head but close.
It is unlikely that you have the original igniter/pick-up in the car as the originals failed before they got out of warranty.
If it is a reluctor type you could check the air gap between the rotor and pick-up or if it is a light emitting pick-up you can look for dirt in between the receiver and light. Not much else you can do unless you know what kind of igniter it is and have some specs on it.
Let me know,
Howard

---------- FOLLOW-UP ----------

QUESTION: so far so good
holding the coil wire close to the engine and removing the ground did not cause a spark but when i shut the key off it sparked.
now you were right about the power i do have 12v going into the coil (disconnected) and i do have 12v going to the cap.
i think that i have the reluctor type igniter
do you know or know where to find the gap specs for the ignited?
and do you have any other ideas where my spark has gone?
thanks for your help
greg

Answer
Hi Greg,
Most ignition systems like that can be tested by just confirming power to the coil and confirm no pulse at the (-) side of the coil with a test light when the engine is turned. Then disconnect the + & - wires on the coil and check the ohms across + to - (about 1.5 for an external resistor and 2 to 3 ohms for a straight 12v coil)
Then connect up the + wire on the coil and remove the coil wire from the cap and hold it close to the engine metal (1/8") and take a ground wire and scratch it across the (-) post of the coil. (you should get a spark. This is a rough test of the coil.
Also, an indicator of a bad ignitor on a failed ignition system is one single spark from the coil each time you turn the ignition switch off.
Most air gaps that I have run across are .012" to .015"
Let me know,
Howard