First time posting to the site, hope someone can help. Have a 1961 Gray Marine Fireball V8 327/255 with side draft and twin one barrel Carters (both rebuilt) that will idle nicely and throttle up to 2000rpm before it begins to run rough and shake. Have pulled distributor and cleaned up fly weights, new points/condenser, cap/rotor, wires and plugs. Timed to TDC per mfg specs. Vacuum advance is questionable but have used manual suction to watch advance arm move. Manually advancing distributor during throttle up has no effect. Any ideals out there??????