your NEXTAR should have come with a inst. manual for the OS 46fxi but for starting the recomended amount is 1 1/2 turns you should run it pretty rich for the first few flights at least 4-5, not so much that it dies when your running it but so there is oil coming out of the pipe you also should be slow and gradual when using the throttle if you jamb it open its also going to cut out on you, nice and easy untill you get to optimum tune. the 2 OS 46's II have are set around 1 1/4 to 1 1/8 turns on the needle each engine is different.
if you have run cars you know the basics of running glow powered engines, airplane engines are a little diferent but not that much,you need less nitro content and more oil usually 5-15%nitro and 18% oil in your fuel for most engines, some brands require more oil for OS engines those are the recomended #