Do you have the engine manual??? In the back of my engine manual for my os it has a detailed chart showing how to set up the needle valve and airbleed screw. For the high speed needle, close it all the way, then open it 2 turns. Start the engine and close it about half a turn, you should be abelt o hit full throttle here. Leave it at full throttle, without the glow plug ignitor on, and slowly close the valve and listen to the rpm's, as soon as they drop off, open the valve 15-30 degrees. This should allow instant transition from idle to full. What kind of engine do you have, a .48 sounds lie it is an MDS, i don;t know if these have an airbleed screw like OS. If it does the website should have a downloadable manual that'll show you how to adjust the airbleed.