Was out riding it yesterday evening, and there was a marked reluctance for it to run properly.

Lots of bucking / surging (they all do it to a degree but this was really bad) also a lack of power just lots of vibration after about 5000 RPM just as it should be coming alive.

Ah well I thought I have bought a "pup" - knackered engine.

Anway, pulled the plugs this morning, they were all white, where they had been a nice brown / tanned colour the last time I looked.

I have done nothing to cause this.

I decided to take it out for a quick run this morning to see if the cooler air would fix it - 2 strokes run better in cooler air.

Anyway I popped in to pick up some fuel and switched the tap to the "prime" position accidentally.

Normal service was resumed.

The tap works off a vacuum, in the prime position it bypasses the vacuum system but means you have no reserve.

I suspect it it the 40+ years diaphragm in the tap that was causing the problem, so will be ordering a replacement.

In the prime position it has run better than ever so the tap must be the issue.

You live and learn.