Air Cleaners for HS Carburetors on
Late Model MGB with Brake Booster
Contributed by Pete Westbay
I’ve been looking for an air filter housing I could modify for my 1976 MGB with dual SU HS4 Carbs. It would need to have a replaceable filter element that was readily available as well as fit the small gap between the brake booster and intake manifold. I also wanted it to appear like it was from the 70’s. I’m still searching for a better “look”.
After looking at many cars, tractors & small engines, I found the filter below that is common to many lawn mowers. I picked up the plastic housing from a local recycle yard. Air cleaner base #795259 -- Air cleaner cover #692298 Tools:
Drill & Drill bits, 11/32nd, 5/16th
Two part epoxy
Bench vice or bar clamps
Build time; 2 Hours.
Begin by separating the back cover from the front. Remember NOT to cut the tab for the hold down bolt! I started with a sawzall, and cut off all the protruding high spots. Then sand all remaining protrusions inside and on the back of the cover with a belt sander. Fill in the unneeded holes with epoxy [shown in photos below]. I added some screening over the larger hole as support for the epoxy.
It may help to use your current metal air filter base or intake gasket as a template. The rear carb cleaner should be as far forward as possible to clear the booster. The intake hole should be drilled on the lower left corner when looking at the back of the piece. I used a 1 inch pilot hole for the intake hole and finished enlarging it with a Dremel. Drill a hole for one hold down bolt. Bolting your template to the work will keep it aligned before drilling remaining holes.
The rear carb cover will need a cut 1-1/2" X 1-1/2" in the lower right corner to clear the
brake booster. Incoming air will still pass through the filter however.
I took the car out for a 60 mile run at freeway speeds with the local MG club and performance was fine. I’ve added louvers (pickup truck rear cab vents) for more airflow and aesthetics (though not needed).
I opted to use the Briggs & Stratton filter #491588S. The Honda filter part #17211-ZL8-023 will also fit. (It appears that the Honda pleats are spaced more tightly, so it may be more restrictive). These are working prototypes. My subsequent sets will be of higher build quality.