QuestionQUESTION: The other day my 1968 MGB MkII ran perfectly when I drove it out of its garage. When I started it again to head off for the day, it started but missed so badly it continually stalled. To cut a long story short, I checked compression - OK, checked fuel supply - OK, checked spark at plugs - weak. I replaced the capacitor and the plugs and it now runs perfectly again. However I have two questions.
1. The spark at the contact breaker appeared to be much stronger after replacing the capacitor. Would this suggest that the new capacitor might be a dud - I thought capacitors reduced the spark?
2. The spark on the HT lead to the distributor cap is much stronger than the one on the leads from the cap (to the spark plugs) when the lead is held close to an earth. Even though everything is running well, does this suggest a problem?
Thanks in advance for any help/advice
ANSWER: 1) The capacitor in the distributor does more than protect the points, it stores energy between sparks. You can test your capacitor if you have a digital ohm-meter. Put the ohm-meter across the capacitor. It should read infinity. Now reverse the two wires. As you touch them, the meter display should jump and display strange numbers before settling at infinity. The first measurement charges up the capacitor, and the second measurement is the discharge. If the capacitor is faulty, it will not hold the charge.
2) Sounds like a classic problem which you have caught early. The spark plug leads on a 68 B have a core of graphited silk. They usually fail after a few years. I would suspect that they are ready to be replaced. Also, I would fit a new rotor arm.
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QUESTION: Thanks, very helpful. I will try the test and it appears I am up for some HT leads. Out of interest, if the capacitor does fail what symptoms does one generally experience in terms of engine performance?
Many thanks.
AnswerDepends how the condenser fails. If it fails short circuit then the engine will not run at all. If it fails open circuit (which is more usual) then the engine is difficult to start, low on power, and doesn't like to rev.
Buy some good plug leads, preferably those with a spiral of stainless steel wire around a central conductor. They cost a bit more, but they will last forever.
