The float level of the SI carburettors is not adjustable. If the swim level is too low, there will be full struckling and dangerous weight loss. This may be caused, for example, by the use of a Cosa float chamber on a SI24/24E carburettor type of the PX models. The Cosa swimmer lies lower and reduces the swimmer level. The spacers offered here raise the float level back to the right level and enable flawless operation.

Note: We do not recommend use on carburettors that still have the standard float lid and float on the PX models (recognizable by the Cosa's unsprung float needle with only Ø4.5 mm instead of Ø5.2 mm). Otherwise, the float level is above the bore of the mouth piece in the intake area, with the result that the engine is flooded with gasoline. The standard carburettors of the Cosa models (24/24H) are an exception. They can also benefit from the spacers because the factory float level is also very low here.

TUNING tip: The spacer is not, as otherwise claimed, suitable for eliminating problems caused purely by tuning the carburettor (lean jerking at full load). The often postulated “vacuuming up” of the float chamber is a myth (the engine couldn't burn as much gas as it gets into the float chamber). Unless the reasons mentioned above (modified float chamber cover, e.g. Cosa in PX carburettor), 99% of weight loss under full load is always an incorrectly designed main air treatment system. If this is taken advantage of (by drilling holes in the air filter base or using an intake funnel or a main air correction nozzle not adapted to these measures), the gasoline level in the mixing tube falls under full load and causes the engine to lose weight and even die out.

Although a float chamber spacer appears to solve this problem (because the water level in the carburettor mixing tube channel is raised), it often leads to problems with overflowing carburettors and/or an overflowing carburettor adjustment in the middle area. The solution is therefore not a spacer but the use of a main air correction nozzle adapted to the air supply. If this is reduced in size (from 160 to 140, for example), the motor runs significantly fatter and no longer requires oversized main jets. This is often misinterpreted and the small main air correction nozzle is replaced with a larger one because the motor was much more agile as a result. The solution here is to readjust the smaller (correct) main air correction nozzle via the main nozzle. The motor will then return to full power with the advantage that it runs stably at the top and is durable. It is also important not to ignore the secondary nozzle system. Its flow rate plays a significant role in the total amount of gasoline available to the engine. If you have previously driven with a large main air corrector and a very large main jet, the middle is often also heavily greased. For this reason, small side nozzles are often used. Therefore, after a conversion to an adapted main air correction nozzle, the size of the secondary nozzle should also be reevaluated. If necessary, this should be enlarged.

About the manufacturer BGM

BGM is a leading brand for high-quality spare parts and accessories for scooters, motorcycles and classic Vespa models that stands for quality, precision and innovation. With an uncompromising “Made in Germany” philosophy, BGM develops durable products in collaboration with leading engineers and under strict quality controls. Whether restoring vintage cars or tuning modern scooters — BGM is the first choice for discerning drivers. Thanks to first-class workmanship and a wide range of products, BGM offers ideal solutions for performance, everyday use and individuality.