Hey Goirish try this,
1. take a unused piece of fuel tubing and slip on end of the fuel tubing on the carb fuel inlet nipple
2. open the carb to just open enough to represent an engine idle, if the carb has a idle stop screw go ahead and use the stop screw. What opening would be used for an idle? A simple large T-pin that you may have sitting around from building on models, or even a safety pin can be used but it needs to be the large safety pin and not a little bitty in that wont make the opening on the carb enough to come close for an engine to idle around 1800 rpm.
3. when you blow into the piece of fuel tubing turn in the low speed needle in until you slow the air going thru the low speed needle to just noticable you may be using your tongue to do this and not your lungs. Yeah I mean just noticable where you may have to be in a real super quiet room so you can "hear the air going thru the needle".
4. The high speed needle should only be turned out NO MORE than three to four turns
5. When satisified with the minute air going thru the low speed needle undo or back off the idle stop screw so your servo has that job and try running the engine again.
6. If you still have engine running problem the next thing i can think of is that you are missing the o-ring from the bottom of the carb to the engine crankcase and too much air is being loss from the negative/positive pulses from the piston and you are not going to get a reliable engine run.
7. If you still have a engine running problem the next thing i can think of is the o-ring at the engine back plate or maybe a paper gasket it is so brittle or damaged or missing and that will allow the engine to loose air from the positive/negative pulses to leave.
8. The last thing i can think of is the front bearing it has to have a shield on the bearing, if the shield is not on the bearing air can be lost from the positive/negative pulses.
In my mind someone bought the engine and let it sit too much and they noticed the bearings rough and replaced the bearings and forgot to replace the gasket on the back plate and add insult to injury they didnt use the proper front bearing where the front bearing is missing one or both of its shields. Good luck and i hope this helps. If you get fed up with it you can send it to me and i can see what i can do with it. I will admit early, way early asp engines were a very cheap knock offs of magnum engines they ran but not very well i know because i had a .46 and it would only run at full throttle and i ran it this way until i leaned it down too far and locked it up lol.