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Removing air boxesThe opposite problem often occurs when air boxes are removed and replaced with filters, or when boxes are gutted or modified. When the restrictions are removed, the carb gets lean because more air passes through and the vacuum in the venturi is reduced. On one model (Ski-Doo MXZ 670) we had to go up 10 main jet sizes (from 290 to 390) to compensate for the air box removal.
This is an extreme example, but often a change of 2 jet sizes is normal. The safest procedure is to richen a large amount if you're not sure, then jet down until you burn clean again. This may take a little effort, but it's easier and much less expensive to change jets than burned pistons.
Filters are popular because they increase performance and make the carbs easier to work on. When used in winter, the filters should be dry, not oil-soaked, and used with an "outerwear" cover to prevent snow from gathering in the pleats and clogging the filters.
This is only a short list of new trends and tricks. Be assured that carbs will be around on the majority of snowmobiles for years to come. Newer and improved carb models will require some new approaches, and the CV carbs now appearing on 4-stroke models is another chapter. There will always be tuners who prefer to change a jet instead of firing up a computer to dial in their favorite race engine.