The .40 LA would benefit from added castor oil. It will run OK with 80/20 synthetic castor blended lubrication, but extra castor oil would help float the crank shaft inside the bushings and the engine will actually produce slightly better compression and more power with an all castor lubrication package.

The ideal fuel for a 2-stroke with bushings instead of ball bearings is 10% to 15% Nitro and 20% pure castor oil for lubrication. Folks who don't like the O.S. Max LA series have probably never tried running them with the proper fuel. This mix is also recommended for the Thunder Tiger GP series and K&B Sportster series of glow engines.

The Kangke SK .50A should be a little more flexible with regard to lubrication, and should run fine on most any sport fuel that meets the manufacturer's recommendations for basic nitro range and minimum oil content.