Atomic mini reed-valve kit Vespa PX/VLB Sprint/VBB/etc

Atomic mini reed-valve kit Vespa PX/VLB Sprint/VBB/etc

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400 grams



[About our Lambretta reed kit using the exact same reed-valve:] 

  • I bought one a while back to fit to an old school Yamaha 200 kit. Back in the day, the DT175 piston for the kit had to have the reed valve windows welded up, so I bought one of the Atomic reed manifolds to save messing around with the piston! It fitted with no alteration to the manifold or the barrel, even the port to manifold area was virtually spot on!
  • I ran one all last year on my (Yam pistoned) Rapido 230. No cutting of fins and plenty of clearance with a 30mm PHBH and remote filter. Mine is a touring set up in a S1 so not lightening quick pick up/acceleration but it's no slouch either and the fuel consumption is equivalent to others in our group who are running smaller engines (i.e., around 12 mile 1L). Hope that helps.
  • [Customized for a Lambretta Luna Starstream]: The Atomic reed block itself needs fettling to fit the Starstream barrel, but not much. My impression is that it is a better quality job than the [other company's] unit.
    -did you get the Mini Atomic? Very little fettling was needed on my Starstream barrel. 
    -The future is ScootrRS Mini Atomic Reed Valve. No fin cutting & no packer needed between inlet & reed valve, just drilled out holes to 8mm & elongated the back hole slightly. Manifold mouth is real small, so plenty of scope for matching to inlet, I'm just mocking now so i'll post some more pix later ... 26 PHBH carb no issues.

Atomic Performance high-quality bolt-on mini reed valve kit for Vespa PX/VLB Sprint/VBB/etc.

What is a reed-valve? Basically a flap that opens and allows fuel in as the pressure in the cylinder needs it, then is pushed closed when not needed. You gain power and responsiveness down low, a huge improvement in fuel efficiency and no spit-back from the carb. People making the change rave about the smoothness of the power delivery.

You do not need a highly tuned motor to use this kit. It is fine for regular motors too.

The kit includes everything needed.


  • good quality reed-valve
  • fits under the panel
  • no need to cut your case
  • rubber manifold with 34mm opening to fit our PWK 24-30mm carburetors (might also fit Dellorto 26-30 PHBH, VHSA 28, Mikuni TM24-30 but check your carb first)

Reed-valve features:

  • good quality Atomic reed-valve for Minarelli horizontal. We also have spares.
  • alloy body
  • fiberglass reeds for optimal Vespa performance (not carbon for super high RPM motorbikes)
  • rubber coated

See our tech notes for modifications needed.

Does not fit smallframes, GS, SS, etc., only 1960s largeframe types with the same pattern as a PX or Sprint.

Tech Notes

  • Check your jetting when making the change. You usually need to upjet a lot. See our tech page for how to do a plug chop.
  • Matching your inlet port to the new manifold is best. One simple way is to tape some plastic in the hole to catch any debris then mark and dremmel the inlet. You can also open the manifold or inlet as much as you want to allow more flow. 
  • A standard Vespa only opens the inlet port when the crankshaft is out of the way. To take full advantage of the reed-valve and allow fuel to enter whenever it is needed you can change to a reed-valve crankshaft or you can modify your own and have a deep groove cut round the crankshaft web to unblock the entrance. A very large inlet port can also open the entrance around the crankshaft web. Raising the exhaust port slightly will help increase power. Please consult a local shop for tuning assistance.

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