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Faulty sparking plug

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bob hughes

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Came across a new one this week end, my BJ7 had just completed a 100 miles run with the club the week before withy no probs. I started it up this week end and immediately it started to fire on 5 cylinders only. With new plugs a month ago I thought the HT cable was faulty, then checking that out I accidently must have pushed the carbon brush into the dizzy head and it had stuck there 'cause nothing was sparking then. Fearing the worst I checked out all the low tension side, all was OK, coil was 100%. That meant that the problem was in the spark distribution, I soon found the pushed in carbon brush and sorted that, but was then still only firing on 5. Number 3 was out, and testing the plug outside, some sparks were seen but seemed to be intermittent, not as it should be, it still would not fire so I used an old plug - all was fine.
So, how could a plug go down so quickly and what could cause it to occassionally spark but not fire up in the engine.?

Bob
 
Long ago I replaced a set of plugs with new, Holly or Champion. Wouldn't run right. Replaced wires, tinkered with carb, replaced distributor cap & rotor, coil, No help.

In desperation took it to a friend with a modern ignition scope. He informed me that the brand new plugs were failing. I didn't believe that this was possible but he said if he replaced the plugs & no improvement, no charge for the plugs & testing.

The car ran perfectly with the new plugs, NGK - wires cap, rotor etc. were not even needed.

So yes - new plugs can be bad right out of the box. Don't know exactly why. Only time it has ever happened to me. Slightly superstitious, I've used only NGK since. Friend had seen it before.

A few dollars spent on a real ignition test can save a lot of trouble & expense.
D
 
Thanks Dave

Had a feeling that you may come up with something, even though it was a similar experience to mine. Strange how it occurs as in reality the system looks to be fool proof, unless of course it is the isolator that is at fault, I have no way of checking.
As it happens my old ones were NGK but the replacements are Bosch.

Bob
 
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