The Holley 2bbls are not progressive like the carter - they're a straight 2bbl
They must be tuned to the motor - specifically the power valve
You have the exact problem I had back some time ago
Visit The Holley technical library
and read up on tuning and power valve selection
Also, which adaptor plate do you have?
The Holley will not work correctly with the cheapo Mr Gasket adaptor plate
There is a link to a better one towards the end of my carb thread
You will eventually need to change the dist as well due to the mechanical advance limiting in your original dist.
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Holley Carb thread