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.

Fitz:

What you have is the K&B "Sportster 65" engine. And if the carb is tight in its mount there's nothing missing - it uses a clamping bolt. If it's loose you might be able to figure it out looking at the parts diagram on the MECoA site.

This engine is an excellent torquer, it does not like high rpm. Keep it below 12K or so, and with castor oil lube it will last a long time.Use a low nitro fuel, any more than 10-15% is wasted. Also, don't be worried by its mechanical clatter, all the "Sportsters" are noisy.

Yours is next to the latest production version, differing only in not having a remote needle from the current engines.

Bill.

PS: No fooling about the castor oil. This engine has a plain bearing crank, synthetics just wont do it. A blend, like Omega or Powermaster is OK. If you can only get all synthetic, add four ounces of castor oil to each gallon. wr.