My 1966 Impala bogs down at wide open throttle. If I am cruising and step on it, it hesitates bad. When I let off and continue to cruise, no problem. The carb is a 4160 Holley 4 barrel. I tried to raise the fuel level in the secondary bowl as described by 'the book', but I cannot really see any gas. Of course, looking thru the small hole is really difficult. Any suggestions?