The 1275cc air filter assemblies use a pair of individual filter housings, one mounted on each SU HS2 carburettor intake. The front and rear assemblies have different part numbers due to their slightly different mounting orientations, but both use the same paper filter element. Each assembly consists of a pressed steel housing with a gasket that seals against the carburettor body, secured by bolts with plain and spring washers.
1275cc Filter Casings
The 1275cc filter casings were bevelled on their upper face to clear the underside of the bonnet. The taller 1275cc engine left less clearance than the previous 1098cc unit, and without the bevelled profile the filter housings would prevent the bonnet from closing. This bevelling is a useful identification point, if unbevelled housings from an earlier or different application are fitted, the bonnet will not close fully and may bounce up while driving.
1275cc Air Filters Maintenance
A connecting strap with a nyloc nut links the two filter assemblies together for mutual support and to reduce vibration. The paper element should be replaced at each major service interval. A restricted element reduces engine power, increases fuel consumption, and can cause the carburettor mixture to run rich, leading to sooty spark plugs and black exhaust smoke.