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DEXTER RACING Item number: DEX30210
DEXTER RACING

Diaphragm intake manifold -DEXTER RACING- Vespa PX80, PX125, PX150, T5, Cosa 125-200 - for carburetor Ø26-28-30mm - PHBH, VHSH, PWK28, TMX30, Smartcarb 26-28)

Suitable for large-frame housings (e.g. Sprint, Rally, PX, Cosa) with long carburettor sealing surface (≥ 70 mm between stud bolts in the direction of travel)
Very good thermal insulation between engine and carburetor
No welding and no adapter plate required
For Honda NSR diaphragm(OEM/aftermarket compatible)
Recommended carburetor sizes: 26-30 mm
169,00 €*
available immediately
Shipping weight 0,6 kg
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DEXTER RACING reed valve intake manifold - Vespa Largeframe (Sprint, Rally, PX, Cosa) - Honda NSR reed valve

Suitable for all engine case variants of largeframe engines (including Vespa Sprint, Rally, PX, Cosa). Conversion to reed valve intake eliminates the original rotary valve control via the crank web. This means that the intake in the engine housing can - and should - be opened/milled for a significant increase in performance. A diaphragm crankshaft(flow-optimized intake cheek) is a sensible option and further increases the potential.

Largeframe PX/Sprint/Rally/Cosa Honda NSR Diaphragm Oil pump free ≥ 70 mm sealing surface 26-30 mm carburetor Made in Germany

Advantages compared to rotary slide valves

Inlet cross-section can be dimensioned large - no sealing edge constraints as with rotary slide valves
Better filling at medium/high revs, stable idling and response behavior
Thermally decoupled carburetor mount - less carburetor heating
No welding / no adapter plate required - clean fit

Technical data & notes

Diaphragm mount for Honda NSR type(OEM/aftermarket compatible)
Design: Stainless steel tube or CNC-milled flat upper part (depending on variant)
Fitting dimension carburettor sealing surface: ≥ 70 mm length between the stud bolts (measured in the direction of travel)
Recommended carburetor: 26-30 mm, depending on setup
Racing part without E-marking; registration possible via individual approval if necessary

Compatible vehicle models (selection)

Vespa Sprint / Sprint Veloce, GT / GTR, GL / Super 150, TS 125
Rally 180 / Rally 200
P125X / P150X, PX125/150 (Lusso/Arcobaleno/MY/Disc) - for housing with long carburetor sealing surface
Cosa 125/150/200

Requirement: Carburetor sealing surface ≥ 70 mm (in the direction of travel between the stud bolts). Short surfaces are not suitable.

Motovespa Iris 125/150/200 and other PX derivatives with long sealing surface
LML Star / Star Deluxe 125/150/200 (Genuine Stella)

Not suitable for cylinder direct intake manifolds (e.g. GS160/SS180) without corresponding housing conversion.

Conversion note rotary valve → diaphragm

Rotary slide valve function omitted. Mill/adapt inlet window(case reed layout)
Recommendation: Diaphragm crankshaft (flow-optimized intake cheek) for maximum performance

Practice & tuning

Adjust carburetor/jetting, intake length and air filter to the setup
Check ignition/AFR under load; ensure heat protection and freedom of movement
Powerful pre-reso range with box systems; peak power further up with resonance systems

FAQ - Frequently asked questions about the MRP diaphragm intake manifold (Largeframe)

A long carburetor sealing surface is required (≥ 70 mm between the stud bolts, measured in the direction of travel). Please check before ordering.
Honda NSR type(e.g. NSR125/NSR150). Compatible with OEM and common aftermarket inserts (NSR type).
No. No welding and no adapter plate required. However, the inlet should be milled to utilize the potential of the diaphragm.
From ~26 mm upwards, typically 28-30 mm depending on cylinder/performance target. The final choice depends on porting, exhaust and application.

Note: Racing product without E-marking. Use on public roads only in accordance with national regulations or after possible individual approval.

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