Intermittent misfire proving impossible to diagnose

[Chancer]

I doubt that it is the following as for me it manifested as fuel starvation after a few hundred yards but I will mention it anyway, it may help someone else.

I had some early weber carbs where the float chamber vented via a crenellated washer under the top jet cover (the one with the brass wing nut) the rebuild kits I used came with a gasket for this joint which I should not have fitted, later carbs vent via a hole going into the air filter.

The problem never manifested itself on a rolling road as the first thing the guys do is remove the jet covers!!!!!

Good advice re the tacho!

It could also be a HT tracking problem, the rotor arm and dizzy cap being suspects, this probably wouldnt be indicated by the tacho malfunctioning. I think there were some dodgy remanufactured dizzy caps that had similar problems, was yours changed by any chance?

[Hapless Biker]

Yes mate, the dizzy cap is an Aldons kit I think, would need to check but another thing to look for, thanks very much!

[Mazzini]

Ballast or non-ballast resisted coil?

[DJ908]

Had similar problems to this on my car some years ago. It turned out to be tracking, or arcing, across the either the distributor cap, or the head of the coil ? cannot quite remember which. But it too, was most frustrating for it only seemed to happen after the car had run for a while. I remember some wise (older ? more experienced) mechanic changed whatever it was ? and was able to show me where the spark had been tracking across the bakelite (?) surface and I have continued to enjoy the car ever since.

Robert

[Watership Down]

What about the spark plugs. As they get hot one or 2 of them could be breaking down. Do you have the correct type fitted ( off hand I can't remember the type)

[billwill]

Dunno if you have found the problem since May, but I would definitely try a new Rotor arm even if you changed the distributor, you might have a bad new rotor arm.

Try a red one from Distributor Doctor.

[miked]

I had lots of bad caps and arms on 23D4 dizzy caps. Same script, would start to miss under load when hot. Failure or insulation. That's why I run 43D. Mike