Lightening the load on a model engine, without changing anything else will make the mixture richer. Any time you change the load you must re-tune the carb. If the engine was smoking a lot at half throttle and died, then its probably too rich. Some engine and glow plug combinations will never fourcycle, they just stop running. Often an idle bar plug will allow an engine to run very rich and fourcycle without stopping. A K&B idle bar plug will be more forgiving of overly rich mixtures while tuning your carb. Once its correct it won't matter what you use.