Put weaker springs on it or stretch the ones you have The last thing is to check both carbs for binding on the throttle linkage, also try looseing the fasteners on the carbs base plate a little, not real loose, just barely snug and try that from the driver seat If is better looser then you know what to work on
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
The last thing is to check both carbs for binding on the throttle linkage, also try looseing the fasteners on the carbs base plate a little, not real loose, just barely snug 
and try that from the driver seat 