My GTX will start and idle, but will not accelerate when I hit the trottle. The engine just chugs. If I slowly ease the trottle up it will eventually accelerate and run quite well as long as keep the rpm above an idle. If I let the engine slow back to an idle and hit the trottle it will not respond and accelerate. I have read it could be the Rave Valve or power pack. Anyone with any thoughts what the cause can be? I have had the carbs rebuilt.