The as-manufactured updraft FAB doesn't fit in the 7 cowling. (I'm sure this holds true for the 9 as well.) Threads abound regarding the narrow clearance between the port side of the air box and the nearby inside surface of the updraft induction cowl. It's way too tiny, so the engine whacks the FAB against the cowl, especially at start-up, unless you alter the FAB design. It's one of those Van's things they simply will not fix.
Alteration for me always meant making a new mount plate, relocating the carb interface as far to port as possible, about 3/8 inch, limited by the FAB-to-carb screws fouling the filter element. That may not seem like much, but it doubles the as-manufactured FAB-cowl clearance at the port side. Watch out, though. The clearance is smaller still where the lower radius of the air box and the cowl radius almost nest.
This project I'm also modifying the top plate, as the above approach still yielded only a 1/4 clearance between FAB and cowl. (It would have touched otherwise.)
Open up the top plate oval hole to port so the filter element can remain closer to its natural round shape. How far is controlled by the bottom edge of the element; it can only round out so far before it starts riding up the radius of the air box. Check that you also have at least 1/2" between the filter's outside surface and the fiberglass airbox for placement of retaining clips and platenuts, as well as allowing the carb sump cutout to remain inside the filter. Now, the carb stud and intake hole pattern can slide about 3/4 inch to port of the factory punched mount plate. The mount plate also must have it's circumference swelled out to overlap the new expanded top plate cutout, and you need to be creative about placement of the platenut/retaining clips. Obviously, you need a piece of 1/16 aluminum sheet for this custom part, so order it with the FAB.
This works for carbs. I know the mixture arm recess won't fit in this modification, so the AFP servos will need the optional mixture arm relocation, which brings with it another set of installation problems. YMMV.
Nothing is ever simple.
Hope this helps.
John Siebold
Alteration for me always meant making a new mount plate, relocating the carb interface as far to port as possible, about 3/8 inch, limited by the FAB-to-carb screws fouling the filter element. That may not seem like much, but it doubles the as-manufactured FAB-cowl clearance at the port side. Watch out, though. The clearance is smaller still where the lower radius of the air box and the cowl radius almost nest.
This project I'm also modifying the top plate, as the above approach still yielded only a 1/4 clearance between FAB and cowl. (It would have touched otherwise.)
Open up the top plate oval hole to port so the filter element can remain closer to its natural round shape. How far is controlled by the bottom edge of the element; it can only round out so far before it starts riding up the radius of the air box. Check that you also have at least 1/2" between the filter's outside surface and the fiberglass airbox for placement of retaining clips and platenuts, as well as allowing the carb sump cutout to remain inside the filter. Now, the carb stud and intake hole pattern can slide about 3/4 inch to port of the factory punched mount plate. The mount plate also must have it's circumference swelled out to overlap the new expanded top plate cutout, and you need to be creative about placement of the platenut/retaining clips. Obviously, you need a piece of 1/16 aluminum sheet for this custom part, so order it with the FAB.
This works for carbs. I know the mixture arm recess won't fit in this modification, so the AFP servos will need the optional mixture arm relocation, which brings with it another set of installation problems. YMMV.
Nothing is ever simple.
Hope this helps.
John Siebold
