Ive found on new engines its most often better to have a smaller prop on it until it has some time on it before getting too heavy on the load. Some engines need to loosen up more and thus need to heat up more so rpm is the ticket. Getting the engine to run at its intended RPM while still rich is important. I run my tapered bore engines on 1" less diameter for at least half-3/4 gallon of fuel before loading it down too much. This allows the engine to be run rich while still maintaining rpm (heat). If the engine is on the tighter side, it may take some time before it will throttle well. I have used and do use the pinch test on my Super Tigres with stock Mag ST carbs because the needles seemed to have finer needle threads so it took more than a few clicks or 1/8-1/16 turn to run rich enough on the top end. Otherwise its always good practice to set the high end to peak rpm first and then set the idle mixture for a good transition. I dont go 30 seconds because I've found in my climate that a clean transition at 30 seconds is a tad lean and usually needs to be a tick richer. The real trick is getting the mid-throttle to not get too rich... Some carbs are horrible for not having a linear mid-throttle mixture. Sometimes a good throttle transition and good top end will still end up with a burbly midrange.
Questionable quality carburetors can make a guy pull their hair out if everything you try doesnt get it to run right... As was said, Magnum carburetors are sometimes suspect so if problems arise that cannot be cured with the normal things, try another carb. Sometimes less nitro is all thats needed to get an engine to purr like a kitten.
Just my thoughts and observations through my limited experience.