I notice the gasket between the reed block and the adaptor appears to be rubber.
I'm going to try a thin piece of neoprene (0.020) and see if that does the trick
All is good vacuum wise from the top of the adaptor using a piece of inner tube to block it off.
I really hate to tie this saw up as it as been great to cut up some firewood. I think it is lighter than the 5200 just by the fact that it has one less label on it.
There should be no use of rubber for gaskets there. Plain automotive gasket material should be used.