Yes its a what vacuum it comes in at I herd please correct if Im not getting it. IM pulling 22 vacuum at idle so I cut it in half per Holley instructions. I put all my squirters in from 28 to 37 still has off cruising surge when u give it gas in one spot of throttle. The bigger main jet I install gets rid of it. Ive gone as high as 60 main but it just destroys power. The 3 chamber muffler has a certain tone u can feel and hear when u run a good leaner jetting and the power is good. Except for that spot or surge if u press gas pedal real slow u can over come it or get threw. There has been many other post I've read with real close situations but no one ever puts what cured there issue.
