For the Rotax 618 UL, the main jets typically differ between the PTO and MAG carburetors, with common stock settings being #135 (PTO) and #145 (MAG), though these can change with altitude, intake silencers, or specific setups, with larger jets (like #160/#170) often needed at lower altitudes or with silencers to prevent running too lean, a common issue for this engine.
Key Jetting Information
Standard/Altitude > 5000ft: #135 (PTO) & #145 (MAG).
Sea Level/With Silencer: #160 (PTO) & #170 (MAG).
Why Different Sizes? The 618 uses two different carburetors, and they require different fuel flows for optimal performance,