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Triumph Spitfire - miss firing spitfire

Please 1971 MK4 spitfire keeps misfiring(as if there is a rev limiter) at 4000rpm.
I have changed the plugs, coil, condensor,distributor cap, rotor arm,ignition leads and the low tension lead and had it tested to confirm it is an electrical fault.
If you didnt take the car to 4000rpm you would never know there was a problem!
T. Dodington

T., Joanna?.
You had it tested and it was an electrical fault? Didn't the tester give you a clue as to where? Ask them!

My guess is worn distributor. The spindle is wobbling about at speed, and the gap becomes random. But a carburettor problem could do the same - worn jet - or a worn out fuel pump - low pressure.

Use a timing light to see if the ignition timing is right at low speed and then becomes ragged as you accelerate - that's a worn dizzie.

in reply to johnD
Thank you very much for your help...when i say i had it tested i mean i tested it with a little red flashy thing that the AA man told me to try when i accosted him in my local car part shop. It fitted onto spark plug and plug lead connected to it..AA man said it should flash consistantly and if it was an electrical fault as opposed to a fuel fault it would die at the misfire (which it did) Would a distributor just "go wrong"? or would it be a gradual decrease in performance as this fault occured from nothing.
T. Dodington

Fair enough! That shows for sure that it is a failure of the spark impulse to reach the plug that causes the misfire. But doesn't tell anything about 'why'. A timing light may help as I said.

It also occurs to me that the condensor might play a part, and that is easy and cheap to change. Try that.

Sad to say, although one might think that faults should gradually appear, the reality is that they ALWAYS occur unexpectedly, in the worst possible circumstances, causing you the maxiumum difficulty. This is known as the Triumph version of Murphy's Law.

This thread was discussed between 28/08/2002 and 29/08/2002

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