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Old 01-24-2012, 11:25 PM
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Using a vacuum gauge to determine carb size

Can a vacuum gauge be used during a WOT run to determine if a larger carb is needed?

I was rolling this idea around & it seems to me that if manifold vacuum showed a steady build in the upper rpm range, the motor (providing it was built to rev) could use a larger carb.

Am I on track with this?

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Old 01-24-2012, 11:44 PM
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Basically, yes. This assumes no restriction from the filter element/air filter assembly and no excessive exhaust backpressure is skewing the results, no vacuum leaks, etc.

I should probably mention that air turbulence across the top of the carb can cause problems that may look like the carb is pulling vacuum at high speeds. This could be due to reasons besides the carb size. This is sometimes found when running a scoop w/o a filter housing, that sort of thing.

Last edited by cobalt327; 01-24-2012 at 11:52 PM.
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