replace fuel lines, personally i would tear down and clean engines, use Denatured alcohol, nitro fuel, or non-chlorinated brake parts cleaner, (i would pull needles out first if using anything but the nitro fuel to clean. them, always skeptical about things eating the o-rings).
bench test electronics including on/off switch, make sure batteries are either replaced or charged up, for both igniter and vehicle/controller.
replace air filter.