I had one of those mushrom air filters in the garage which was missing the element so I some foam to size but now @ around 2800 rpms and under pressure, the engine just dies (loses all power). If I easy my foot of the accelator, it pulls again. Is it because the foam is too dense and not letting enough air through when needed?
Thanks
Raf

Raf , take the foam out and see if it still does it.
If the foam was restricting it that badly it would probably suck it down the carbie.

Took the foam out last night. Worked OK this morning. Gotta get the right filter then

You can actually buy air filter foam, but you end up with more than you need (I still have about a square metre left from some I bought about 8 years ago, but it's starting to break up now...)