nm9stheham said

New tank and lines too? The 'brown stuff' would not be from fresh fuel boiling off. Older 'gunk' is more likley, as MO sez.

BTW, consider a full heat shield, not just a spacer. The spacer does not prevent heat from radiating up from the intake and into the bowls.
Like this:
Holley 108-51: Insulating Carb Gasket Heat Shield Fits Holley Model 4150&#0153 and Model 4160&#0153 Square Flange Carbs | JEGS

Click to expand...