Got it, thanks Ron, that at least is one mistake i won't be making now!! I feel a lot more confident about this now and if things don't go well with riding then i will try taking out the jets. I found getting the block out, with care and balsa wood and hammer - and then putting it back, straightforward. thankfully.

it is great to have this website and all the knowledge that goes with it. with thanks again and all best peter

The upper half of the jetblock is very easily damaged/distorted and lots of them are.....especially if the carb has a larger bore, like the M21, here the top only stands on 2 very thin brass legs.

To tap out the jetblock without putting force on the top half I made this very simple tool from a spoke and a piece of aluminum.






BR Michiel