welcome to the world of gas motors!!
sounds like your running it too lean. with the main dial on top (high speed needle) turn it about 1/4 turn counter clockwise. performance will go down but see if it helps first. the one by the air intake is the Idle screw like you said and the is how high the engine idels without any imput from the gas/brake. You want it so that the car doesnt move at all without any imput from the sticks. turn it clockwise i THINK to lower the idle RPM which will make is idle without moving. Don't do it too much or it won't start very easily. the last needle (low speed needle) which should be on the little thing that pulls in and out when throttle is applied is for acceleration. for my car I do a pinch test. basicly pinch the tube going into the carb from the gas tank. If it dies all a sudden (less then 3 seconds) its too lean (adjust needle counter clockwise) if it goes for longer then 3 seconds before dying then its too rich (adjust needle clockwise). When properly tuned most cars should have pretty good top speed and acceleration. Make sure you arent overheating your engine. (steam/smoke coming up from the glow plug) like remember when i was driving my car off your jump? there was a little steam coming from the top of the cooling head. Hope this helps a little. anymore questions just ask