6 mpg entitles you to Holley Gold membership. I remember a mate walking into the workshop one day with a big smile; he changed one POS Holley for another & doubled his mileage! Yep, went from 2 to 4 miles per gallon.
10* initial timing is nowhere near enough with that combo. And if you are not using vac adv, that is only making it worse. Worse, because the engine is inefficient with it's current ign timing; inefficient, gobbles more fuel.
Your engine needs at least 30* of timing at idle [ not 10 ], & maybe as much as 40*.
Read these links & learn.
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