Michael,

The screw you are talking about is mainly the stop screw for the throttle barrel inside the carb. There usually is no need to adjust it.

I usually hate to answer a question with a question but I have to in this case.

You mentioned it will idle abot 30 seconds then die. Does it just shut off or does it spit and die.

If it just shuts off it's most likely too lean. If it's spits and sputters then dies it's a little to rich.

The low speed mixture screw/low speed idle screw is located inside the arm where your throttle linkage/clevis is connected to. You will need a small jewlers screwdriver to get to it. On page 10 of the manual you will see a diagram that explains throttle position. There are 2 lines, 1 for 1/4 throttle and 1 for 3/4 throttle. Thise 2 lines are pointing right where the screw is. It's easy to miss because it is actually inside the arm. That is the screw I was saying about making only 1/8 to 1/16 turns on.

Just follow my procedures. Here they are again for the low speed needle just to make it easier for you

BTW...Page 15 of the manual shows the screw in the carb breakdown

http://www.osengines.com/manuals/46ax-manual.pdf

Bring the engine to idle and let it sit for about 10 seconds. Now quickly move the throttle to no more than 1/2 throttle, 1/3 throttle is usually pretty good, the engine should respond slowly and blubber and maybe spit fuel out the muffler, that's OK, it's rich. Bring the engine back to idle and stop it. Now turn the low speed needle 1/8 of a turn clockwise (leaning it), no more than 1/8 turn please and restart the engine. Run it up to full throttle and hold it there for a few seconds to clear it out and bring it back to idle and wait 10 seconds, now quickly bring it up to 1/3 throttle. If it is still spitting fuel and slow to respond stop the engine and turn the low speed needle clockwise 1/8 turn again. Restart the engine and repeat the procedure for the low speed needle. Make sure that when you go to adjust the low speed needle you do it with the engine off as you will be very close to the prop.

Keep repeating the low speed sequence until the engine responds instantly up to 1/3 throttle. Once you have that back the low speed needle out 1/16th of a turn (richen it) , then take the engine to full throttle and back to idle. Wait 10 seconds and go to full throttle again quickly. The engine should now be responding instantly. If this is an new engine leave the low speed a little rich for about a gallon. If this engine is already broken in then do not worry about backing the low speed needle out the 1/16th turn.

The reason I am having you go to no more than 1/3rd throttle is because the low speed needle is in effect up to half throttle and then it transitions to the high speed needle.