The great majority of B16 engine Volvos sold in the US were (and many still are) equipped with the B16b engine. This means the cars have a slightly higher compression ratio, a little hotter cam profile and twin H4 SU 'side draft' carburetors.

This has proven to be an excellent combination, blending good performance and gas mileage with outstanding longevity. Of course, nothing lasts forever and changing fuel blends along with many, many heating/cooling cycles are taking their toll on the fuel delivery systems of these cars. The pushrod Volvo engines are not 'crossflow' designs as are the newer OHC B21/23, this means that the intake and exhaust systems must coexist in pretty close proximity. This is especially true on the SU equipped B16b engines. The distance between the float bowls and seals in relation to a VERY hot exhaust manifold on these engines can be measured in inches or less! Add to this, modern fuels, with a more volatile and sometimes more reactive alcohol/injector cleaning components and it is easy to see why this system is prone to leaks around the rubber/cork seals. Of course, in this design the fuel tends to leak directly on the exhaust manifold. Even slight leaks will lower the fuel level in the float bowl enough to make restarts harder, especially with a warm engine in hot weather. Hard starting is problematic on 6 Volt starters and potentially more so in converted 12V systems!

SU-Filters has designed a kit to address these issues, stopping the leaks, increasing fuel mileage and improving starting performance, especially in extreme temperature conditions.

Below is a graphic illustrating the Carburetion part of the solution.