The problem was a perished inlet rubber ( the one between the carbs and the reeds).it had split in two on the l/h cylinder!

Does anyone know if it's the same part on a 21?

And if so does anyone have one?

It will be a few weeks if I order new and I want to be out this weekend if possible.

Thanks

21 and 28 insulators are different. The 21 has holes for the boost bottle, the 28 doesn't.

Buying a new one pretty much ensures that you get a nice snug fit with no leaks.

Thanks for your help.