With the engine sitting at about 1900RPM in 4th the revs intermittently drop by about 500RPM very quickly before shooting back up to 1900. It does this twice in about 10 seconds then drives fine for 15-20 mins then does it again. I've changed the plugs, rotor arm, cap and points, but not sure if the problem is electrical of mechanical to be honest.
My hunch is that it may be over fuelling so I'm going to check the condition of the plugs tomorrow.
I think I'll check the compression of the cylinders while I'm at it.
If any one else could shed some light on what they think the problem could be I'd be grateful!!
