RE: K&B .65 Sportster
Turbo.gst hit it right on the head, as far as I'm concerned.
If you're looking for an OS type of engine, believe me, this isn't the one. But if you are looking for a "poor man's four-stroke", it is a perfect match.
I have two Sportster .28 engiens and one .65 Sportster. I cursed the .28 engines at first. Why? Because I was expecting them to run similarly to my old K&B .40 and .61 engines of years previous. They do not. At least, they do not right out of the box. These engines are crudely built and they take some babying to get them just right. Lots of oil and it should be castor oil, or one hell of a lot more synthetic oil than you are used to using.
My first experience with the Sportster .65 was when I flew a friend's kit built Sig Kadet Senior. I forget the size of prop on the nose, but it was much larger than the traditional 11x7-8 prop that a sixty would normally spin. The engine had been flown quite extensively on this Kadet Senior and was well seated. It was a *****cat to hand start, idled and transitioned without stumbling at all, and once running, did not quit until it ran out of fuel. Who could ask for more? Well, it was also quieter than the average sport engine too.
The Sportsters were designed with a muffler that was effective and which provided a bit of boost when compared to other design mufflers of the period.
The carbs were designed to run without muffler pressure initially. Later, K&B caved in and fitted the engines with muffler nipples. Didn't make any difference, but it did keep the modelers from complaining about it.
Early versions (many years of production) did not have bronze bushings fitted to any part of the engine. K&B had a lifetime warranty on these engines. When the crankcases or connecting rods wore out, they would replace them for free. Later iterations of the engines were fitted with bronze bushings. Again, this may have been an attempt to quell the complaints of some folks. None of my bushingless Sportsters have needed new crankcases or connecting rods as yet - so go figure. There was one fellow at my Salem County R/C Club field (Ray Hubshmitt), who seemed to take delight in seeing how many times he could get K&B to replace his thoroughly worn-out .45 Sportster crankcase for free. Ray used to fly A LOT, but he always used fuel with at least some castor oil in it - maybe all castor oil.
So, if you are looking for an engine that will pop into your model and run just like the OS, Enya, Webra, YS or Irvine that you took out of there, look elsewhere. The K&B Sportster series is not for you.
If, however, you like exploring new territory in how differently engines can behave (engine freak - like Hobbsy, Jim and me) due to metallurgy and basic design philosophy, the K&B Sportster Series engines can be loads of fun. Just don't be in a big hurry and buy some fuel with at least half castor oil lube, preferably all castor lube.
And remember to have plenty of patience. This IS a hobby my friend. The journey is far more fun than actually getting there.
Ed Cregger