So, yeah. Spent a lot of money getting it ready for trackdays this summer: tyres, carb kits and ultrasonic cleaning/setup, plus the usual oil and filter and rad flush and so forth. I thought because it had had carb trouble (old fuel turning to varnish) that that was the problem. But it started and ran, just not well and would not pull through the revs or out of a corner. So, um, yeah.

My point is that if you only have a hammer, every problem looks like a nail.

It took a third party to step back and say "Have you started with the basics before chasing esoteric fixes: compression test, leakdown test, valve clearances etc then move on to peripherals.."

All I can say is "Doh" and I'm posting my tale of woe as a warning to others.

Now I have to decide if I want to rebuild it, or just quit it and buy something modern for trackdays. I like the idea of a 428cc one (hey, if its in bits, why not?) but the cost is well up there....

It may just be valve clearances that's tight, so I'd check them before condemning the engine.

Sadly not. valve clearances checked and compression checked too