If installing a open type or hi flow air filter a upjet is required. The same goes for a performance exhaust system. Stock carbs tend to be jetted lean from the factory to begin with. Air filter and exhaust mods increase air flow through the combustion chamber of the engine,thus rejetting is needed to satisfy the increased fuel demands of more air. How much of a retted is needed? That is variable upon the individual engine. I tried a 80 first and was to small. A 88 was to big . A 85 jet worked prefectly in my paticular scooters setup.
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