RE: K&B 6.5 Engine
Old Formula One engine? You might try Clarance Lee for parts. Certainly he knows how these engines are set up in terms of head clearance and rear rotor spacing. I had 10 of them about 20 years ago, but sold them off years ago when I switched to X-40's (ST). They will run good for sport flying with 15% fuel, and can run on 65% if you don't mind changing pistons and sleeves after lean runs. Use a long plug, standard element like a K&B 1L, it's not too critical. Keep ground rpm in the range of 20-21 K. Start with a APC pylon prop with about 7 1/2 pitch and cut down to get into the rpm range. I think the rear rotor is set at about 0.004 to 0.006 for proper needle operation. From time to time you should surface the rear rotor backend with 600 paper on plate glass with light oil to make flat. You will burn about 2 oz of fuel per minute with 15%, more with the higher nitro fuels. For long life, I wouldn't exceed 30 or 40%, as the needle get more critical. Fly rich or shut down as soon as it starts to go lean over the top. Oh yea, head clearance depends on fuel, altitude, air density, and prop load. Start with plenty of clearance (0.012 -0.015) and the needle will be broad and easy to set. As you bring down the head, it should remain easy to set the needle. If the head is too low, it will be difficult to set, and you will start to see glow plug damage. Good luck, have fun.