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A3

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The Tomos A3 engine is a simple two stroke 49cc engine with a two speed automatic transmission. It is found on Tomos automatic models from the 70's until 1992. Depending on the model of A3 engine, they produce one to two horsepower with a maximum RPM of 4000-5500. This motor uses a Ducati 6v points type ignition. The A3 has a special flywheel alignment pin instead of the traditional woodruff key used by most other moped manufacturers. For more information on this pin, please see the woodruff key page.

1991 and Previous Technical Specifications

  • A3 Engine
  • 49cc two stroke
  • 38mm X 43mm Bore/Stroke
  • 8.5:1 compression ratio
  • Automatic 2 speed transmission
  • Encarwi 12mm Carburetor (#50 jet) or Dellorto SHA 14/12 (#53 jet)

Maintenance Information

  • Gearbox oil: Type A or Type F Automatic transmission fluid.
  • Spark plug: NGK B6HS, Bosch W4A2, Champion L82
  • Spark plug gap: 0.5mm
  • Timing advance: 1.8-2 mm BTDC
  • Points Gap: 0.35-0.45 mm

A3 Versions

The A3 came in three different versions -- the SL, GM, and SP (20, 25, and 30mph versions, respectively). For more technical data on the three models, read this.

Related Articles

Manuals

Repair Links

An overview of the flywheel, points, transmission, and how to replace the transmission fluid
A look at the gears and internal spring mechanism
Toolbox