Yes like they said, probably too rich, you should read up on the fuel mixtures and how they work, all the combustion is in the ratio of the nitromethane, and oxygen, this is how the engine fires after the glow has stopped sparking, when the fuel mixes with the oxygen and gets put under pressure it will combust, the low speed needle, and high speed needle, work like a garden hose, opening them "rich" allows more fuel, were closing them "lean" lowers the amount of fuel, this is all very important when making these engines run, and prolonging the engines life, flooding, spitting out unburned fuel and sometimes stalling are signs to too rich fuel, were if it over heats, or has either no to little blue smoke, it may be too lean, also will want to check the idle, on 2.5 engines, if i am correct, the idle gap should be 0.7-1.0mm, the high speed factory setting is 4 turns out from closed, and for the low speed needle, it should be flush with the ring around the head of the screw, also make sure that when the throttle servo is in neutral, that the throttle arm on the carb is completely closed, never turn up your idle by adjusting the servo, hope it helps, you can find most instructions through google and some searching for tips and tricks, it is either a fuel problem, or maybe the engine needs a rebuild, check compression, clean air filter, exhaust, for no clogging, also, i have heard, that even a pin hole in a gasket can cause problems, this is why we use "after run" oil, were the methanol in the fuel will dry out the gaskets....
.....do you take the temp at the glow plug ???