knightmagic,

This may be a long post so bear with me.

It's sounds as though you may be lean. The low speed needle does not adjust the idle, you transmitter does that. It only adjusts the mixture. A rich low speed will make the engine blubber and respond slowly to the throttle and it may deadstick, especially if idling for several seconds, like on a down line in the air or just plain old idling on the ground. A lean mixture will allow the engine to respond quickly but will deadstick if the throttle is opened quickly but may idle forever on the ground.

I am assuming by your post that you have checked for air leaks going from the tank to the high speed needle and from the high speed needle to the carb and that your fuel is fresh. If you have air leaks between the high speed needle valve you will see bubbles in the line from the tank all the way to the carb. If the line between the high speed valve is leaking you will have bubbles between the needle and the carb only. The little "O" ring on the high speed needle will also cause leaks. Any leak will make it difficult to tune.

I also assume you are using the proper sized prop. Anything else will lug this engine and cause it to overheat and no amount of richening will help and the glow plug is good

These engines are usually rock solid. I have had more than my fair share of them and usually sold them with the plane. I can name several that are still flying after setting all winter.

If you need it, here is the manual http://www.osengines.com/manuals/46ax-manual.pdf

Having a tach handy will greatly help, but you can do this by ear. This will take about 10 - 15 minutes to do and if everything else is as it should be you will have a powerful engine that is rock solid

To tune this engine, lets get it back to the factory settings on both needles. Turn the High speed needle until it seats (Clockwise) and then back it out (counterclockwise) 1 1/2 to 2 turns. Now take the low speed needle and seat it (clockwise) and back it out (counterclockwise) 3/4 turn. Be sure not to seat the needles tightly, just seat them until you feel pressure.

Now start the engine and leave the glow driver on. Let it warm up for at least 30 seconds. Make sure the plane is strapped down tightly or is being held firmly. Now go to full throttle, the engine will probably stumble and blubber but that's OK right now, it's rich. Once at full throttle start turning the high speed needle clockwise (leaning it) until the rpm starts to pick up, When first starting this, turn the needle 1/4 turn and wait a few seconds for the engine to clear. Keep doing this until the RPM does not get any higher, once you get to that point turn the needle counterclockwise to rich it so that it looses about 300 rpm. Back off to about half throttle and remove the glow driver, now repeat the high speed needle procedure. Once you have the high speed set, go ahead and lets work on the low speed needle.

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.

Hope this helps...

By the way, this will work for most any OS 2-stroke engine...