I am attempting to repair an EXT special (550 cc). The problem is with the engine. The engine starts easy, idles fine, but when attempting to increase engine speed, the engine is very boggy and cannot move the sled. Even with drive belt off it has a hard time to get to 6000 rpm. Engine has been totally gone through mechanically and all internal workings meet factory specs. Pressure test is excellent. Carbs have also been worked and are good. Factory main jets are installed (310). Previous owner tryed different jets with no luck. All coils meet factory resistance values and reveil no visual problems. CDI cannot be tested by myself. Timing required retarding the stator ass'y as far as possible to achieve factory specs. As engine is reved up the timing light has trouble operating and timing advances 6 degrees or more. Seems to me I have an electrical problem. Suspect CDI as this is only electrical component I cannot evaluate. Can anyone knowlegably confirm this or point me in the correct direction. I hate buying parts and using the trial and error method of resolving a problem as parts are not cheap.