need help with over heating of K&b.40

[tewitt1949]

Hi all. I posted this in another area then I found this area which might be better.
I have a old K&B 40 motor that I've had about 22 years. It has always performed great and still does. I haven't changed anything internal infact I've never had it apart. 15% nitro fuel and I've even added extra castor oil which someone suggested.

Anyways, it will run on the ground or in the air for about 1 1/2 minutes 1/2 to full throttle. Then it starts to sag on rpm's. Finally quiting 30 seconds later. At that point, if you wet your finger and touch it, it sizzles. I've always run a 10-6 prop. I tried a 9-6 and same thing. It has great compression and runs like a raped ape at first.

I tryed richening the carb until it starts to blubber from being too rich, but will still heats up. I do have a pressure line to the tank from the muffler. I really hope to find the answer to correct this heating problem as this motor really runs great.

There is no cowl or any thing around the motor, completly exposed.

Why?? I can't figure it out. Any idea's???? Thanks Terry

[MECOA]

Check these things

http://www.mecoa.com/faq/fuel/tank.htm
http://www.mecoa.com/faq/carb/needle_aero.htm
http://www.mecoa.com/faq/carb/debris/carbdebris.htm
http://www.mecoa.com/faq/overheating/overheating.htm