RE: Fox .40 BB engine
First a bit of model fuel in the carb will loosen up the carb and the bearings. The varnish that is built up is softer than the steel bearings so it won't hurt to turn it over to get the new fuel to disolve the varnish. One you get it started the heat will finish removing the sludge.
You could use gasoline but it's more dangerous to do so and you have to be very careful.
The .40BB was a great motor in the mid 1970 when it came out. A real power house motor that is pretty comprable with todays .40s.
Also Fox has a very resonable repair program. They only charge for parts for their repairs. Or at least they did the last time I checked, a couple years ago.