I have plenty of experience with cold weather running, they will not warm up if you can get it to run rich enough.
It's never good to rip a nitro engine at less than 150 degrees, or as low as 100 when it's freezing out.
Sledman? It's probably cold out isn't it? Try warming the engine up with your wife's hair dryer first.....hehe...Also keep in mind that cold air is more dense, which means you need plenty of fuel to mix with it. Never lean your needles to get the engine warm. If it's not warming up you may have...