Engine hesitates when C4 kicks down

[WarEagle]

I recently hooked up a kickdown cable from my 300 ci (bored .010 with a 240 head) to my c4. It kicks down like it should. However, the engine revs up good for 1-2 seconds, then 'bogs down'. I have a 450 cfm Holley 4bbl on an Offy dual plane intake, medium Crane cam and headers.
I think the initial performance is from the primary pump shot of gas, but not sure why it bogs after that. I did put in a one step stiffer spring in the vacuum secondary diaphragm, thinking the 450 cfm might be a little big for the motor. Should I go back to the stock secondary spring? I think it is fuel related, just not sure how.
Thanks,