Yep, I think you guys who went for the Orbit type clunk were right on target. I have removed the tank and clunk and there was considerable restriction when sucking through the clunk line with the clunk attached. The clunk was opened up, ye gods, its amazing the engine ran at anywhere near full power. No wonder no dirt can get through the screens they are amazingly restrictive. The four "windows" have very fine screen mesh which when removed considerably eased the flow restriction. Inside the clunk there is another filter made of a sort of porous plastic. When that was removed all the restriction cleared. With THAT plastic removed the two feed holes were revealed and they are TINY, about 1.5mm square, totally inadequate for our purpose, certainly for a 36 pound thrust engine.

I have attached the pictures and if the clunk is NOT the cause of the vapour bubbles it certainly WAS a potentially serious problem now, thanks to you guys, removed.

The other picture is of some of the final details going onto the Hawk, this morning it was the inner widscreen and MDC.

Thank you ALL again SO much for your input.

Regards, David.