Guy's I have several of these engines and like them very much, however they seem to be having a castor build up inside  the engine and I am having some trouble getting the steady runs that they once produced.
 What suggestions do ya'll have for restoring the run's ?? 
 They still have real good compression, so that tell's me that they aren't worn out.
  Randy Smith and others your oponions please...........
                 Thanks a lot...

How much castor are you running in them, the most they would need is 1\4 castor. You may want to run a synth blend with only about 5 or 6 ounces of castor in the fuel

Randy

   Thanks for the reply's fellow's..
  Guy's I am running 22% oil half castor half synthetic, I will run all syn in it as they are Ball Bearing engines.
   Thanks for ya'll's help..

According to the Tower catalog, the SX was a "special purposes" (hotrod) engine, with pretty high rpm range, and ABC. The ABC is good, but the rest isn't, for stunt. They were used by some in 80mph combat, but at $125 each, that was thought to be a bit steep for what many consider a 'fun' event. It appears like OS has dropped the SX and come out with the new AX, in ABL cylinder configuration, whatever that may be. I don't understand why they wouldn't keep the same design and adopt new cylinder technology (if it's better) to it. Unless that technology isn't as good as ABC, of course.

Short answer is: Probably not for your purposes, unless you want a go-fast combat-ish model for reflex tuning on occasion.    Steve