Your problem is impatience! There are probably multiple settings that are not quite right, and your inexperience is causing you to chase the problems. You need a methodical approach to tuning that an experienced ear will really help you get through. Get your hands on a tachometer to make this easier.

New motor, new glow plug, new fuel, you can probably rule those out as problems.

First, get the motor running, and with the glow igniter attached, get it up to full throttle. Now remove the igniter, and adjust the HIGH speed needle for peak RPM and then back it back out (richen the mixture) until the RPM drops about 300-500 RPM.

Now that the motor is up to temperature, and the high speed needle is set, bring the throttle back down, and adjust your THROTTLE trim to about 3000 rpm.

Now allow the motor to sit at idle for about 30 seconds. Now pinch the fuel inlet line and listen carefully to the engine. If the engine rpms rise slightly, your low speed needle setting is slightly RICH. If the engine just dies, the low speed needle is lean. Release the fuel line before the engine stalls. Slowly raise the throttle to full for a few seconds to clear things out and warm it back up, then bring it back to idle. Let it set for another 20-30 seconds at idle, then punch the throttle to full. If the engine hesitates then goes to full throttle, the LOW speed mixture is RICH. If the engine sputters and dies, the LOW speed mixtures is probably LEAN. If these two tests give you inconclusive results, just guess if its rich or lean.

Now, turn the engine off by putting your finger over the carb inlet or the kill switch on your radio (don't use the throttle trim yet).

With the engine off, make a SMALL adjustment in the LOW speed mixture screw (its the one inside the throttle arm). The adjustment should be 1/8 turn or less. Its very easy to completely miss the optimum setting if you make to large a change.

Now restart the engine, and (this is important) reset the HIGH speed needle for peak RPM and richen to 300-500 RPM below peak. Did I mention this is important? Now repeat the tests as before. Is the engine behaving better or worse? If its better, keep making adjustments in the same direction until the engine will go from idle to full throttle without hesitation. If you cant tell if its better or worse, keep making adjustments in the same direction until you can tell.

The key is to make only one adjustment at a time, and then see how its performing. The good news is that once you have the low speed needle set, you probably won't have to touch it ever again.

Good Luck

Brad