Adjusting Progressive vs Synchronous Carburetors

All adjustment procedures are the same for Progressive and Synchronous carbs, however it is important to understand the differences between the two carb styles. Progressive carbs idle through one barrel and one mixture screw, then transition to the secondary barrel which has an additional idle (low speed) jet. Synchronous carbs have individual idle jets and mixture screws for each barrel. They also have an additional air bleed screw and lock nut. The air bleed screw is not used for idle adjustment or quality. The settings for this screw should be closed. The adjustments settings for synchronous carbs tend to be half of what is recommended for progressive carbs. Example, if a progressive carb is set at 2 turns, the synchronous carb would be set at 1 turn.

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