intermittent Backfire

[Joss_D]

My car developed a slight cough about a month ago, and backfires occasionally. As of yet I've not been able to suss out what the problem is. I originally thought it was an air leak, as it seemed to have all the symptoms. Fast idle speed, backfiring at lower speeds when a little throttle was applied, and not reaching the red line.

So I bought a gasket set, but before it arrived, the backfiring seemed to have stopped. No spluttering at lower speeds, and reached the red line perfectly well. Since then, there have been days where I've taken it out and it's run fine, and days where it's had all the symptoms I mentioned above. Sometimes it changes within the space of a journey, feeling fine at first, then backfiring later on.

I don't really want to dismantle the carbs and all that, to replace all the gaskets only to find that the problem hasn't been cured. Any ideas?

I really hope it's nothing related to the fuel/air mixture, as the car was tuned on a dyno about 3 months ago. Although, even after it was tuned, the idle speed remained at about 1000 rpm, which isn't ideal in a 3-synchro box. I'm surprised first gear has any teeth left at all...

Anyway, any help would be much appreciated!

[Pandora]

sticky choke?

[timo]

It may be a coincidence but I had just the same problem with my Frogeye, it would run fine and then occasionally start to backfire and then misfire and sometimes cut out completely. I tried everything including stripping the carbs, replacing the coil, swaping the ignitor back to points. When it eventually refused to start at all, I spotted a small hole about 1mm diameter going up vertically inside the rotor arm. An arc had been leaping from the rivet in the arm to the distributor spindle, eventually breaking through the material leaving a hole.

I replaced the arm with a blue one from H & H and have had no problem since.