Air Filter - BGM PRO REV - with hole, Vespa Dellorto SI20, SI24E, SI24H, SI26 - for Vespa PX80, PX125, PX150, PX200, Rally 180, 200, Cosa 125, Sprint

BGM Air Filter with Relief Hole for Vespa SI Carburetors

The BGM air filter with relief hole was specially developed for higher-performance Vespa engines with SI carburetors. A precisely positioned hole above the main air correction jet specifically influences the fuel-air mixture at higher RPMs.

The goal here is not to allow as much additional air as possible through the filter. Rather, the hole alters the pressure conditions in the air correction system and ensures that the mixture enrichment—which normally increases as RPM rises—begins later.

• Relief hole above the main air correction jet
• for Vespa SI carburetors 20, 24, 26 mm
• Improved throttle response in tuned engines
• Smoother high-RPM performance
• Wider usable power band
• Successfully tested even on high-performance engines with over 20 PS

Why the relief bore is useful

The stock SI air filter is not a traditional performance restrictor. However, its tuning is designed for the RPM range of a stock engine, which typically reaches its maximum power between 5,500 and 6,000 RPM.

More powerful cylinders in a touring setup can still generate significant power even above this range. It is precisely there that increasing fuel enrichment in the SI carburetor can limit high-rpm performance. The relief bore addresses this issue and enables a fuel mixture characteristic better suited for tuned engines.

Confirmed on the test bench

Adjustment via a relief bore has proven effective over the years in many Vespa engines. A direct comparison between engines with and without a bore in the air filter base shows that the engine with the relief bore revs more freely and can maintain its power over a wider RPM range.

Especially when combined with high-torque touring cylinders, this allows for better utilization of the SI carburetor’s existing potential without fundamentally altering the proven air filter design.

A very cost-effective solution for increasing power and torque and broadening the usable RPM range.

Note: After replacing the air filter, the carburetor jet settings should be checked and, if necessary, adjusted to match the specific engine setup.