Please note: These pages are part of my RS 125 Workshop Page on my web blog and they are not related to the manufacturer Aprilia/Piaggio. These are self-written repair instructions, hints, tips and tricks for the old Aprilia RS 125 with two-stroke engine until year 2012. This blog is operated by a private individual without commercial background and without any benefits. There is absolutely no warranty. Any liability for any kind of damage that may be related to information from this website is totally denied. Use at your own risk.
The reed valve block, which by the way can also be found like this in the Rotax Max in kart endinge, offers a few minor places where you can optimize a little.
For a better sealing effect, the reed valve carrier can be sanded with fine sandpaper on a flat surface (grit 400-600 is quite sufficient), the sealing surfaces are only milled flat and a light gap is visible here in the original state. Whether this has any measurable effect in practice is doubtful, but this measure costs nothing and an improved sealing effect will not have any negative effects.
There is also room for optimization on the intake manifold itself. The end that protrudes into the reed valve case is not perfect in terms of its geometry. There are inserts that are placed on the front of the intake manifold and optimize the flow while cutting off the tongues of the original intake manifold.
Reed Valves
Boyesen reeds are available for the original reed valve support, these consist of shorter deck valves that open at low flow and a larger valve underneath that also opens at higher gas flow.
Caron reed valves are also widely used. Here, however, you should only buy from reputable manufacturers. Cheap carbon reed valves should be used with caution. If they break or fibers come loose, this can cause fatal engine damage (crankshaft bearing, connecting rod or cylinder damage!). Carbon fiber composites have extremely good tensile strengths, especially in relation to their weight. This does not mean that they can be bent well and often. Carbon fiber composites are not suitable across the board for every application; you can buy them as sheets in all qualities and cut all sorts of things from them – including avoidable tuning reed valves . These are offered at ridiculous prices on various online portals.
The RS 125 already has fiber composite reed valves as stock, whose mechanical properties can change after a few years of operation. If new carbon reeds are installed, they can feel better than the old, worn original reeds.
Reed Valve Kits
In addition to replacement reeds for the original reed valve carrier, complete reed valve kits are also available from some manufacturers.
Moto Tassinari VForce 3
The VForce 3 reed valve block is center split and equipped with carbon reeds. For installation, the intake manifold must be cut off, a nozzle is not supplied.
Italkit Double Prisma
Like the VForce 3 valve block, the Italkit Double Prism valve block is split in the middle and comes with an intake manifold fitting the 34mm carburetor.
The reed valves here are made of a material that is at least visually very similar to that of the original Rotax reeds.
Polini Superval
A somewhat older product from Polini, the Superval diaphragms, consist of a large number of small diaphragms. This product is listed here more for historical reasons.
The information given here about the jetting is quite interesting: The rebound waves to the carburetor are supposed to be lower, therefore the size of the idle jet is to be reduced by about 20%. At high speeds, the “aerodynamic shape” is supposed to draw in a larger amount of air, which is why the main nozzle is supposed to be enlarged by 20 to 25%. Whether these valve design is actually more aerodynamic, I do not evaluate at this point.