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carberatorjets and tuning


johnmolitor01
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I have a 47 panel with a 1960 straight six . It has a fenton manifolds on it. two single rochcester carbs. It is running to rich. I get 14 miles per gallon with it. I reset the floats an checked the jets.. I can't read the numbers on the jets to see what I have. does anyone know what size jets I should start with , an any help would be appreciated on it.

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You need to attach a vacuum gauge and adjust the carb's mixture screw to the highest vacuum. Get a UNISYN ...... Disconnect the linkage between the carbs and sync them with the throttle screws to the lowest idle speed. This really affects the mileage

 

Once correct the vacuum should be pretty steady depending on several things including the cam your running

 

I get about 18MPH with a built 302 GMC With the 228 I got well over 20

 

Feel free to PM me if you still have questions

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Since you have the Rochester type B carbs:

 

Check the airhorns to make sure they are not overly warped. The Rochester B is infamous for warping airhorns due to too few airhorn screws.

 

Why do I mention this when you ask about jets? Because there is a vacuum passage controlling the operation of the power (economiser) valve going from the bowl (center casting) to the airhorn (top casting) which should be sealed by a gasket. When the airhorn is sufficiently warped, the passage is not sealed. If the passage is not sealed, the power valve is open when it should not be open, thus augmenting the fuel supplied by the main jets, and the engine runs rich.

 

Jon.

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