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progression holes?

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...I know WHAT they are, but I'm b*gg&red if I know how they work.

They are the group of small (<1mm) holes dilled into the body of your DCOE/DHLA's and are covered by a brass threaded plug.

They somehow ensure a smooth PROGRESSION from steady throttle opening to acceleration without flat-spots/hesitation.

...now I pass the baton to someone else....

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Progression holes provide the fuel for the critical transitional time just off idle (closed throttle) and full throttle which is called 'progression', they are drilled thru to the top of the carb barrel and do nothing until the throttle plate passes over them at which time the moving air draw fuel through them, the further the throttle opens (and therefore the more air inducted) the more holes are uncovered.

The fuel is metered to the progression drillings by the idle jets and it is not uncommon for the drillings to be innappropriate for the engine's needs and sometimes need re-drilling to adjust them.


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