Have you thought about fitting a reed valve inlet and a boost port. I did on a lambretta engine which is very similar to a Bantam cylendar. Added 6bhp with same carb and exhaust system.
Terribly intrusive soundtrack. At one point speech is (almost) audible but is drowned out by jangly guitars etc. Ugh!!! I am sure what is being said is very interesting but I cannot hear a damn word - and then get deafened by the alleged musci starting again, Please sort it out.
