For the high speed jet, because a RC engine could seize in seconds if it is too lean, I like to do spark plug checks between runs of steady thropttle, and I do several runs to "work up" to full throttle while checking the plug b etween runs, adjusting, and making another run with more RPM until your going full throttle. If the plug is dark in color (black or brown), you are safe to increase RPM for the next run. If you can't get a good color to your plug while your working up to full throttle and your plug is running white or very light, even if your high speed jst is a whopping 2 turns out, you have some otyher problem like a carb problem or some fuel delivery problem. If you don't fix it, you stand a chance of seizing.

Rememberr, a hot engine under load needs more fuel than a cold engine on a stand with no load. So no matter what method you use, the engine should at least be up to operating temps, and a clean air filter should be used also.