No u have to drain it or the engine will explode..............J/K


u do not need to drian it u jsut fire it up like normal the only thing ull notice is it smells funky buring at first but after half a tank it will smell like normal nitro what i do is take the filter off and the fuel line off and inject some after run into the carb and just turn over the engine.........this will coat you whole engine inside...........i use to also take the plug off to inject after run there also BUT i stoped doin it to lower the risk of geting dirt and grime inside the piston