Nitro engines are not meant to idle for long, 30'ish seconds is what you should be aiming for. If (when the engine is fully warmed up) the engine will not idle for longer than 10 seconds then you should adjust the low-speed needle. An erattic idle (revs change dramatically although throttle is stationary) is an indication of a lean setting, whilst a rich idle will cause the revs to gradually fall and then stall the engine as the crankcase fills with fuel. Hitting the throttle after 10 sconds of idling will also give a good indication of mixture (lean/rich/perfect). You want the engine to spool up immediately with no stutter off the line. If the engine pumps out a lot of smoke (bogs) then it is too rich, whilst a lean setting will also cause the engine to bog - but it will sound as if the engine is struggling to get enough fuel. When you have then engine tuned properly, then adjust the idle opening.

Also, when you first start and engine you should not leave it to "warm up". Idling while stationary will generate much less heat than running the engine at higher revs. In reality, as soon as the engine starts, use it normally - this wil get the engine up to temperature.

I do not believe there is a pressure problem or air leak - this would generate other symptoms. Priming the engine to get fuel into the carb is necessary on all engines.

I hope that answered all of your questions.