The modern take on powerjets is to turn them off after peak power to extend the rev range. This assumes that you are happy for your engine to rev that much further past peak power & on many buckets perhaps this is not so good unless you have uprated the crank assembly. The jet will start to flow, depending on its position. Some don't seem to work well without an airbox if they aren't very prominant, or perhaps if the suction isn't so much (putting big carb on a smaller cylinder). In some cases they are best blocked off presumably if the air jet doesn't match very well & is tending to increasing richening with airflow as it is.
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