NARAKU 85 cc cylinder for Vespa 50, PK and APE - high-torque and suitable for touring
The 85 cc Naraku is an enlarged version of the 75 cc Naraku cylinder with a 50 mm bore. For use in the Piaggio APE50 three-wheelers, however, it was turned down by 1 mm at the cylinder base compared to the Naraku 75 and the same dimension was left at the top edge of the cylinder. The control angles were reduced to 152°/98° (exhaust/overflow) in order to allow the cylinder to start assisting even earlier in the rev range.
Improved acceleration is therefore not to be expected on a Vespa V50/PK with the original gearbox compared to a Naraku 75, as the cylinder reaches the end of its rev range very quickly. The gears must be shifted through quickly in order to achieve reasonably acceptable acceleration. However, this characteristic can be used to good effect with an extended gear ratio to turn a fifty into a durable long-distance tourer. To do this, use a longer primary (3.00) and a 19/19 mm carburetor with intake manifold. The 10.7:1 compression ratio cylinder runs very well with the equally high-torque banana exhaust from BGM (BGM Touring) or an original banana. PK models can very well continue to use the original exhaust, provided it is not coked. After the obligatory adjustment of the jetting (main jet min.74), checking the pre-ignition (the standard pre-ignition of 19° is retained) and the use of the spark plug with the correct heat value (NGK B8HS or Bosch W4AC), a long-lasting and powerful touring package is ready.
TIP: Please always fit piston rings carefully. Some pistons have trapezoidal profiled piston rings (so-called keystone rings), which only fit in one installation position. If the ring does not move freely, please loosen it carefully and reinstall it 'upside down'
.TUNING TIP: Simply raise the cylinder using a 1 mm foot spacer and turn the cylinder by the same amount on the upper sealing surface. This lifts the control angles to the same level as the Naraku 75, making the cylinder significantly more torquey.
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