advice help 40s please.

[taxi]

Hi, my twin cam has this odd running at very part throttle, but is fine if nailed off the line. been on the rollers and seamed ok. What happens is as you drive it slowly it shudders very bad and the fuel pressure drops off,push down a bit harder and its fine and pressure back and it flys. My question is would a duff ignition side effect the fuel pressure on driving? Any help cheers, i think ive checked nearly evrything on the car but some one might have come accros it before. The carbs have been apart floats ok and its fine on the rollers,tank been out aswell ????? can text your answers to 07979044495 cheers all