If you find that the engine will not chop off clean or is slow to come back from high rpm's when you lift the throttle, this is a sign that the pop-off pressure in the carb is too high. The cure for this is to lower the pop-off pressure. If you experience loading-up problems, this is a sign that the pop-off pressure may be too low. The cure for this is to raise the pop-off pressure. As a general rule of thumb, the pop-off pressure will be from 8 to 12 lbs, and is a tuning factor that you can adjust for the altitude