Turns out, this means the pilot setting is on the Rich side and a smaller pilot jet should be installed. If the engine idles at its highest RPM at over 2 The engine idles at its highest RPM from 0-1 turns out this means the pilot setting is on the Lean side and a larger pilot jet should be installed. The preferred setting window is between 1 and 2 turns. Continue backing the airscrew out until the engine idles at its highest RPM. Screw, to allow the engine to catch up with the adjustments). Next turn the airscrew all the way in until it bottoms out, once bottomed out slowly back the screw out a ¼ turn at a time (give the engine 10-15 seconds between each ¼ turn of the Then turn the idle up so it is idling about 500 RPM’s higher The ideal procedure for setting the screw in the correct position is to warm up your scooter engine to the proper operating temperature. Proper adjustment of the airscrew can offer direct feedback on the necessary setting required for the pilot jet. The airscrew works with the pilot/slow speed system of the carburetor, mainly affecting the engines initial starting, The carburetor to be slightly adjusted for variances in atmospheric conditions. The airscrew is a fine-tuning adjustment designed to allow In the end, you'll probably need to invest in a range of jets, and tune the engine accordingly.The air screw is a small (5mm in diameter) slotted brass adjustment screw located on the inlet side (air filter side) of the carburetor. The guidelines above are just starting points, or a rule of thumb. There is no shortcut or magic formulas for high altitude operation, you'll just have to work through it. Once again this is assuming the engine ran properly at sea level.įlat Levels and Fuel Pressure: No changes for High Altitude operation.
For example, if you used a jet size of 140 at sea level, you would install a jet size of 220 at 4000 feet, 250 at 5000 feet, or 270 at 6000 feet. Again, this is assuming the engine ran properly at sea level.Īir Jets: You will normally need to increase 2 jet sizes for every 1000 feet, once you go above 3000 feet. For example, if you used a jet size of 160 at sea level, you would install a jet size of 140 at 4000 feet, 135 at 5000 feet, or 130 at 6000 feet. Main Jets: You will normally need to drop 1 jet size for every 1000 feet, once you go above 3000 feet. Of course, this is assuming the engine ran properly at sea level. For example, if you used a jet size of 50 at sea level, you would install a jet size of 40 at 4000 feet, or 35 at 6000 feet. Idle Jets: You will normally need to drop 1 jet size for every 2000 feet, once you go above 3000 feet. This way you'll always have the original factory settings if you ever need to refer or go back to them. Don't use a small piece of scrap paper that could get tossed out in the trash, write them down inside the front cover of your Ford or Weber service manual, or anywhere you'll have a permanent record that won't get lost. Instead, remove the top of the carb and actually remove the jets, emulsion tubes, air correctors, check the sizes, then WRITE THEM DOWN. Never rely on a list you found somewhere on a website or in a book, that says what your carb might or should have came with. Make certain you designate the differences, if any, between the primary and secondary circuits. In other words, what parts were in the carb when you pulled it out of the box. This applies to both single and multiple, side-draft and downdraft carbs.įactory Calibrations and Set-Up Before you go tearing into your carb, the very first thing you need to do is make a record of the factory calibrations or set-up. However, jetting the carb properly to get the correct fuel mixture is the key in maximizing performance. Simply put, there is less air to mix with the fuel. Keep in mind that there is nothing you can do to stop some power loss at high altitude, as this is going to happen, due to the lack of oxygen at high altitude. While there is no exact formula for tuning or re-jetting a Weber carburetor for high altitude operation (4000 feet or more), the following steps should help to maximize the available power.