I recently acquired a K&B two stroke engine which is brand new. The only markings on the motor besides the K&B logo is a :91 stamped on the rear plate. My concern is that I compared the size of this motor to an old OS 61 i have and they appear to be the same size. Also, on the case below the carb, there appears to be a small allen bolt and brass plate. On the other side of the body under the carb(Side where the needle is) there is a threaded hole where i assume something is supposed to go. A visit to K&B website did not clarify the size of the motor so i could not dowload a parts diagram. I curious to figure out what size this motor is and what is missing from the threaded hole. trying to post pics. hope it works.