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The Different Versions
The Yamaha BWS and BWS NG (New Generation) in the UK are known as the Zuma and Zuma 2 in the USA. This motor is also used in a lot of other machines including Aprilia Amico and SR 93, MBK Rocket, Sorriso, Booster, Booster Next Generation and Target, Garelli SR and Pony, Fantic Big Wheel, Italjet Bazooka, Pista, Pista 2, Reporter, Scoop and Yankee, Lem Flash, Ghibli and Tornado, Yamaha CRZ, CT and Spy.
The early versions in the UK were of Japanese origin. After 1992/93 they were made in the MBK factory in France and the engine units were assembled under license by Moto Minarelli in Italy. There are small differences but they are basically the same machines.
Rev Limiters and Restricters
To comply with the 30mph moped legislation restrictions are made by a spacer in the variator front pulley which restricts the gearing and by a rev limiter. The washer between the front pulley halves is easily removed. On early BWS motors the rev limiter can be removed by disconnecting the red wire from the CDI (Capacitor Discharge Ignition) unit to the wiring harness. If the engine will not run after this wire has been disconnected then you have the later CDI. The later CDI has a retarded ignition timing that makes the motor’s power output fall considerably when the motor starts to rev out, making replacement of the CDI the only cure.
There are several replacement CDI units available. Some maintain a fixed ignition timing to RPM well in excess of what the motor will take. Other CDI units retard at a fixed rate so that they match the standard ignition timing at 8,000rpm then continue to retard gradually.
On a motor modified to run to 10,000rpm with power and a high compression, a retarding CDI unit gives better results by matching the requirements of the motor more closely.
Exhaust
After the motor has been derestricted the first major improvement in power comes from changing the exhaust system. The original system is more a silencer than a performance enhancer, so power increases of 60% to 70% are quite feasible.
Most exhausts run at higher RPM than the standard system. This means that transmission alterations are necessary to make the engine run at this higher RPM. Exhausts such as the LeoVinci SP3 and Handmade give good power increases similar to the Giannelli Sport Cee and NRX. The SP3 and Sport Cee exhausts run at around 8,000 to 8,500rpm. The Handmade and NRX run at 9,000rpm.
Although this extra RPM will give greater speed and performance it is better to use a lower revving exhaust with 70cc cylinder kits, as these kits tend to run at higher RPM than standard, and gear up the machine to obtain the top speed required.
The Yamaha BWS and BWS NG (New Generation) in the UK are known as the Zuma and Zuma 2 in the USA. This motor is also used in a lot of other machines including Aprilia Amico and SR 93, MBK Rocket, Sorriso, Booster, Booster Next Generation and Target, Garelli SR and Pony, Fantic Big Wheel, Italjet Bazooka, Pista, Pista 2, Reporter, Scoop and Yankee, Lem Flash, Ghibli and Tornado, Yamaha CRZ, CT and Spy.
The early versions in the UK were of Japanese origin. After 1992/93 they were made in the MBK factory in France and the engine units were assembled under license by Moto Minarelli in Italy. There are small differences but they are basically the same machines.
Rev Limiters and Restricters
To comply with the 30mph moped legislation restrictions are made by a spacer in the variator front pulley which restricts the gearing and by a rev limiter. The washer between the front pulley halves is easily removed. On early BWS motors the rev limiter can be removed by disconnecting the red wire from the CDI (Capacitor Discharge Ignition) unit to the wiring harness. If the engine will not run after this wire has been disconnected then you have the later CDI. The later CDI has a retarded ignition timing that makes the motor’s power output fall considerably when the motor starts to rev out, making replacement of the CDI the only cure.
There are several replacement CDI units available. Some maintain a fixed ignition timing to RPM well in excess of what the motor will take. Other CDI units retard at a fixed rate so that they match the standard ignition timing at 8,000rpm then continue to retard gradually.
On a motor modified to run to 10,000rpm with power and a high compression, a retarding CDI unit gives better results by matching the requirements of the motor more closely.
Exhaust
After the motor has been derestricted the first major improvement in power comes from changing the exhaust system. The original system is more a silencer than a performance enhancer, so power increases of 60% to 70% are quite feasible.
Most exhausts run at higher RPM than the standard system. This means that transmission alterations are necessary to make the engine run at this higher RPM. Exhausts such as the LeoVinci SP3 and Handmade give good power increases similar to the Giannelli Sport Cee and NRX. The SP3 and Sport Cee exhausts run at around 8,000 to 8,500rpm. The Handmade and NRX run at 9,000rpm.
Although this extra RPM will give greater speed and performance it is better to use a lower revving exhaust with 70cc cylinder kits, as these kits tend to run at higher RPM than standard, and gear up the machine to obtain the top speed required.
