I have a old k/b motor it has 61 stamped on the side and below the it has d0065006. I was wondering if some one could tell me what size this is, And if they were any good. It seems to have good compression.

The K&B .61 is a good motor. Try a 12x6 prop, maybe a 13x6.

The K&B 61 is really nice old motor. Ball bearing. Different carbs over the years. Just remember that it's not a Schuerle screamer. Run it at a nice slow pace, not over 10-11,000 rpm. Be sure to run some castor oil in the fuel, maybe Sig 50/50 syn/castor, 5-10% nitro. Parts aren't too hard to find-they made a lot of them.

I have a k&b 61 on a trainer with a perry carb on it it is a very good running engine like kdheath said they are not power houses . Meco said max rpm is 12000 i get that or a little more with a 11-7 prop Thea's engines are good runners never a dead stick with it . .

I was about to say they do run well with a 11-7 prop at 12,000 RPM. A modern engine would turn that prop at well over 13,000 RPM, but weighs much more. Great engine for a heavy .46 sized plane, or a light .60.

Thank for the help guys. Now all i need is something to put it in someday.