Once you get it running, run it at full throttle and adjust the mixture so that it runs slightly rich of peak rpm. Get the high-speed needle right first, then slow it down to idle. If it quits right away, it is more than likely lean on the low speed needle. If it idles but hesitates when you quickly increase the throttle setting, it's more than likely rich on the low speed needle. Adjust the low speed needle accordingly, then run it at full throttle again. You might need to adjust the high-speed needle again at this point because the low speed needle still allows fuel through while the engine is running fast, and will affect the high speed settings. Keep working at it until you can get it to run well at full throttle, idle, and get a good transition. Also, when you first start the engine, leave the glow plug connected for a minute or two until it gets warmed up, and don't start messing with the needles any more than necessary to get it running until it is warmed up.
Charlie