I have a brand new tower hobbies .75 I have been trying to break it in but I can't keep it running. Can someone tell me how many turns I should set the low end screw?

Sounds like the low end is too lean or closed to much. Open up a turn and see what happends. Several ways to check. I'll try and ramble off a few.

1. disconnect your fuel line from the hipple on the carb. and attach a separate line to the nipplie long enough to blow into.
2. open the carb up to its approximate idle position.
3. completely close you low end needle.
4. Open up your high end a few turns.
5*****Now at the same time, blow into the fuel line and open your low end until you here a hissing noise. With this done, your low end is now in the ball park.
Start it up and dial in your high end to peak rpm.

If you can get it running smooth, lets check your low end again.
This time while the engine is at and idle (hopefully) disconnect your fuel line from the carb. it the rpm increase right before the engine quits, the low end is to rich, therefore close it a tad (1/8 inch). If the rpm just goes down and quits, low end is to lean-open a bit.

These are not barnyard methods but are in most owners manuals. i use them religiously and my engines run fine.

appreciate your help. I will try it out and let you know how it worked

If you still have trouble, it might be your plug

Enjoy,

Jim