I did do some performance tests on one of my K&B Twister .61 engines. it was quite impressive. The more rare tuned muffler really livens them up but it ran really well with the Evolution(aja Jett) tuned muffler too.
I posted the RPMS I got with different propellers here. It seemed to like 12x8 props really well too.
http://www.rcuniverse.com/forum/m_11...m.htm#11027798

I just got me a Kraft 61 from Bruce, I really like it. It makes really sweet enginey type noises.

I will try a 12x8 prop. I have a 13x6 on it now. Good engine!!

I take a handful of different props in the appropriate size range and bolt each one on, tune the carb for it and fly . Lets me know first hand which one I like best. I find I usually end up with one of slightly lower pitch than I would have thought, probably because I like the throttle response.

Originally Posted by 1ruffdog

An OS 55 AX has more power than the Enya .61 for about $150. With K&B there is always a concern about parts. The original K&B company no longer exists.

Cheers,

Mecoa acquired K&B several years ago and stocks parts for most K&B engines.