<VV> backfiring

[Paul Abel]

Finally got the 65 monza sedan 110pg on the road. I've put about 200 
miles on it, and the valve train seems to have settled in fine (sat 
15yrs) It starts right up, and idles good, no lifter noise. Up to about 
40 mph it runs pretty well. Problem is, when I get on the highway and 
get it up to speed, it bucks and backfires, hard to keep a constant 
speed. I've been told the carbs need adjusting. I tried setting them 
according to the manual, but I'm having trouble getting them perfectly 
balanced. Is this really my problem? I've had misadjusted carbs before, 
but never had the bucking / backfiring thing happen. Could I have a bad 
condenser? Gas tank was cleaned, lines replaced, new fuel pump, inline 
filter.

Paul Abel.