There is no such thing as a factory needle setting. A good starting point is 1.25-1.5 on the low and 1.5 on the high. That does not mean its safe to fly it but a good place to start the engine and see what you have. Dont run an engine on the ground at higher thottle settings for more than a few seconds to get a feel for your high speed needle setting. No two engines are the exact same and no two carbs are the same. Throw in prop load, atmospheric conditions, aiflow in cowl, exhaust systems, cooling systems and the variables keep on changing things. What I like to do is fire the engine up, let it warm up a couple of minutes, run up to full power to clear it out and build some heat then come back to idle, goose the throttle and if the engine hesitates or dies its to lean on the low end, if not lean the low until you hear the hesitation when goosing the throttle then slowly richen the low speed needle until the hesitation is gone. I then set the high speed needle to a point that it will not clear out or the engine is four stroking, then lean it a bit until it just wants to clear out to a two cycle burn. It may bounce around a little between two cycle and four cycle. Then you have to fly the plane to let the temperature come up to maximum and listen to the engine. If you hear it four stroking land and lean the high needle about 1/8 turn at a time. Fly and check it again. You should get a bit of four cycle when flying horizontal but when you pull vertical it should clear out and have a good clean two cycle burn. You should tune the engine to pull the hardest on an upline and not worry so much about what it does in horrizontal. I know I shouldnt say this but if it makes you feel any better we have not ever repaired one single burned up 50cc engine. That is saying alot considering 50cc planes are the most common entry level gas airplanes and the BME50 is one of the most popular. Japanese engineer asked me what is difference? House burn down and engine burn up?

Keith
BME