Inliners International Forums General Discussion Engines carb circuits and gearing/tire sizing

The main metering circuits generally uses a main jet and an air bleed orifice. Without the air bleed orifice, the main jet tuned for mid range rpm's would tend to run too rich in the upper rpm range. So if you increase the main jet a few sizes and don't change the air bleed, your specific tuning will not stay in the best fuel/air ratio band throughout the mid to high rpm range, especially as the weather temperature changes.