Whenever I have a student show up at the field with a limiter on the high speed needle, the first thing I recommend is to take it off. Then with their approval, I help them remove it. Better to teach them how to properly tune the engine from the start.

Your problem sounds like you're setting the high end too lean. (you said it revs high for a few seconds then drops). The statement "If I let it idle more than about 10 seconds, I never get to BRRRR - it starts to rev, then dies." leads me to believe your low end is too LEAN. Just to be sure, are you sure you're adjusting the low speed needle? I don't want to seem insulting, but some first timers don't recognize the difference. This is different than the high speed needle. The low speed needle typically requires a very small (jewelers screw driver), and is located inside the ring around the throttle arm. I just looked at the Evolution manual on line, and it does show a limiter collar on the low speed needle. I'd get rid of it.

I had a Megatech engine I just finished breaking in that I actually had to modify the carb internals in order to get the low speed needle adjusted correctly. Its set up with a tube and sleeve arrangement. The low speed adjustment moved the sleeve to adjust the mix. The sleeve was a few thousandths too long. The engine was exhibiting similar characteristics as yours. The difference between rich and lean at the low end is difficult for the novice to determine. Rich, after 20 to 30 seconds, the engine will hesitate, and then rev up due to the excess fuel that builds up in the carb. Lean, the engine will hesitate, then die because there isn't sufficient fuel in the carb already to support the extra air being dumped into the carb when you punch the throttle. Its subtle.

To test, richen the LOW speed needle by 1/8 turn, start the engine, and reset the high speed needle to 200-500 rpm below peak to the rich side. Try the punch test. Keep trying this by making small adjustments in the LOW speed mixture until you're convinced (try up to a full turn) its not getting better. If its getting better, keep going until it doesn't get better, or you start to get the hesitation before the runup.

Good Luck.
Brad