you cannot run the spacer behind the VF3's, it will allow the center cage to push back and out during hard acceleration.
the intake is what holds it in.
if the VF4's assemble in the same manner as the vf3's ?
you cannot run the spacer behind them, only in front of between the cage and cylinder.
running in in front of any reed cage results in a lower rpm power band,
behind reeds raises the power band in the rpm range.
unless you are running a spacer to purposely alter the powerband rpm's, or for larger carb clearence,
use it as a paperweight.