Royal bought their engines from Leo engines the owner is the nephew of the owner of Thunder Tiger. Leo has his own website and makes engines for Megatech as well as others in the car market likt TNT. These are very good engines are indeed copies of both the FSR (2 piece case) and SF series (one piece piece case)of OS. The only problem is in the idle circuit of the carb. The stop screw is to thin and allows the barrel to move when you adjust the idle needle. To deal with the problem make adjustments with the engine not running or when you push in the screw driver you will push the barrel and shut off the engine. The other choice is to make another stop screw. Remember the stop screw rides in the groove in the barrel to cam the the barrel position into the stop position as well as adjuct the idle mixture strength.

By the way these are the type of questions this website was set up to address.

DDD