I have a nexstar with the 46 fx engine. I went out for my first flight with my instructor yesterday and it was great. We had a ton of engine problems though. My instructor says that the engine is just breaking in but man this is getting to be a pain. We're having trouble getting it to idle, and the engine is cutting out alot. I ran a tank of gas through it today in my driveway and took some temp. readings. Running it rich it gets to 200 f. If I lean the engine out it climbed to 285 f. I'm just wondering manily if anyone has any break in suggestions and what temp is too high for this engine. Thanks

I presume that this is an ABC type construction engine. In which case, the piston will be tight until you've ran about a dozen tanks of fuel through it (at least!). After than, it should free up a bit and idle better. Make sure you run it really rich while you are breaking it in so as not to damage the engine. Do this for a dozen tanks of fuel and you should notice the improvement.
In the mean time, I'd set the idle a bit higher so it shouldn't cut out as easily, but still leave some movement on the trim (or if you've got a throttle cut switch, use that) so that you can still stop the engine when you land.

WALL all of the nexstars are supposed to have been broken in from the factory, the trouble your having is typical of mostly all of the nexstars. you have to adjust the lower end mixture screw, i would start buy turning it in buy an 1/8 this is the screw at the bottom of the carb, you will also have to change your mixture screw as well,when it is adjusted correctly you should be able to snap your throttle and the motor should respond emediatly.

Do NOT run an ABC engine rich! ABC engines use a tapered sleeve so the piston gets "squeezed" at top dead center to maximize compression. The construction is such that the sleeve and the piston expand at approximately the same rate in order to maintain compression.

Running it rich will cause the piston to expand at a faster rate, which will cause it to excessively wear the sleeve. Then when the engine is brought up to proper operating temperature, compression will be low. NOT what you want from your new engine!

The best way to break in an ABC engine is to run it on the "slightly" rich side of "peak", at full throttle, for about a minute, then shut it down and let it coolfor a couple. Then repeat.

Proper (operating) head temperature for most of these two stroke engines is about 300 degrees. 200 degrees is way too rich.

I too would look at the low end setting, but it will take a few tanks to get it to the point where it runs reliably.

Good luck,
Dennis-