Hi!
OK Here we go!
There is nothing wrong with the OS LA series of engines and has never been. There carbs are simple airbleed carbs and are so good that nothing else is needed.
There is absolutely no need for drilling the airbleed hole larger! At least if you live/fly at sea level and fly under normal air temperatures from -20 to +40 degress centigrade.

For good engine behaviour it's vital that you follow some simple rules. Which are...

Always use good fuel. This in the OS LA case means using fuel that contains 5-15% nitro.When it comes to oil percentages it's good to use at least 20% if you are using commercial fuels. Castor oil or syntetic oil or a mix doesn't matter. Personally I use 15% all syntetic oil (Motul "Micro" or Aerosynt 2 or Aerosave) but Klotz oils will also be fine, but use 20%.
I mix my own fuel as most people do over here, but as long as you use commercial fuel, everything will be just fine. But see to that you run at least 5% nitro and that the fuel is fresh. Do not use more than 15% nitro!I personaly use 5% nitro in all my engines.

The airbleed carb idle needle should be set half open. That is the standard setting. Open it slightly if the engine doesn't have instant throttle respons.
Al OS engines can sustain long periods of idle running and still bark to life instanly if just set correctly.

The way you adjust the high speed needle is vital.
Not to rich and not too lean.
By holding the nose of the plane straight up for a few seconds you can check if the engine is set correctly. Always set the needle a little rich from full rpm. Do not shake the plane when doing this , just hold it straight up!

Correct glow plugs are also vital.
For your engine and 5-15% nitro an Enya 3 or OS 8 is what I personally would use.There are of course other plugs that will work too.

When it comes to props a 10x7, 11x6 or 12x4 is what I would recommend if you have a low winged sport model or slow high winged trainer type model.

Tank position and size is also very,very important.
For a .46 engine a 240-300cc (8-10oz) tank is what should be used. Anything bigger and you risk having engine setting problems due to engine could not cope with such large pressure variations inside the tank.
It's also very important that you follow the simple rules that says: "Always place the tank so that the center of the tank is inline with the carb intake orifice when plane sits horizontal". If you follow these simple rules any engine will run well, throttle perfectly and have instant throttle respons even after several minutes ideling, upright or inverted doesn't matter.