An update on recent developments! I think I found the issue setting base idle. Basically the head was warped and had one bent exhaust valve. I tried everything and couldn't sort it. I noticed that it had developed an oil leak from between the head and block so sent it away to be tested. I'm surprised it ran as well as it did!

I've now got it back after having a skim, new valve and 4 new exhaust valve seats cut. Just need to fit it and test it.

Lee