28PSI made good power but was brutal on drive belts. An 8mm x 30mm HTD would last 1/4 mile if I was lucky. I converted to twin vee belts and I could get a full meeting out of a pair. At 28PSI jubilee clips could not hold the rubber hoses on the inlet pipes, I brazed studs into the pipes and used straps to stop the joints parting
These engines are tough as old boots, especially if fitted with a Jawa conrod

BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro no senshi"