i am working on my friends thundercat. the other day we got it out and it ran down the field twice fine. he stopped and let it idle and when he went to take off it would just fall on its face. we have replaced all the plugs and cleaned all the carbs and set them how they are suppose to be. its got great spark and it is getting fuel. we just cant figure out what it is. is there some kind of wireing that wont let it go if something its wrong? i was also thinking about if there is a sensor on the throttle lever? we have been working on this for 2 days and we are stumped!! we tried putting gas in the cylinder and that did nothing. we are thinking its someting simple because it ran good then just like went in to limp mode.what could it be?