Just to concentrate on these, the ST 15 may be either the old G20/15 or the later G15 but both most likely have a cast iron piston so I wouldn't use a fuel with less than 20% all castor. Neither of these engines are your normal run-of-the-mill sports engines and are rather collectable.

The Enya 45 is a fantastic engine but not as powerful as later engines because the 6001 model was originally intended for CL stunt. It came in two versions, the first had twin rings (like mine) then changed to a single ring in about '71. Don't use Morgan fuel (either Coolpower or Omega) in this because their fuels don't have enough oil content (only 17%). Personally I used 25% all castor in mine.

The Enya 35 has a cast iron piston and really needs 25% castor. With this type and amount of oil these engines are legendary for their life span. It's rumoured that someone managed to wear one out but no one actually believes it .