Hi there. I had acquired this older K&B .20 engine a while ago and am now in process of building a PBF to use it in. I have not flown a nitro engine in approximately 20 years and am unsure of how to tune and or adjust this thing. The things I am not sure of are the carburetor and how to set it. I do not believe that it is original. The needle is very short. Also, the other thing I am unsure of is the rotating larger disc on the needle side that the needle screws into, as it has a + and - as well as 3 lines on top of the carb. Any help would be greatly appreciated.

Also in one picture, you can see that the upper right side lug where the screw screws into is broken off and was missing. Will this be a problem?

Looks like a Perry Carb and also appears to need to be rotated 180 degrees so the fuel line nipple is pointing to the rear of the engine. Just my guest.

Yes it looks like a Perry carb that is on "backwards" (just rotate it 180°). The rotating disk is for the low end and it is very sensitive, minute adjustments is the key. The the lines indicate neutral position and maximum points for a leaner and richer settings, yes it doesn't need a larger span than that (!).

The mounting of the backplate is a little compromised but if it doesn't leak then the crankcase damage shouldn't matter.

Awesome. Thanks for the help, as i now have something to look for now.

Not just the carburetor, looks like the whole head has been rotated, never seen an exhaust outlet on the left!

That's a K&B Sportster .20. The cylinder and head can be rotated to use the exhaust on the right or left. Whichever orientation it's run-in as is the way it should stay until the piston/liner wear out. They cannot be used as a rear exhaust engine however.

The Perry Carburetors are notorious for needing o-rings replaced. Do this and clean the carburetor out extremely well or you will fight to get a good tune out of it.

Your is the older sportster 20, the current model has a K&B carb:
http://www.mecoa.com/kb/56/5600.htm
And here is the manual for Perry carbs:
http://www.perrypumps.com/Carburetor.pdf
http://www.perrypumps.com/prod01.htm

Thank you all for the help.