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Derestricting
The standard motor gives approximately 3.2bhp and 30mph top speed. The gearing is restricted by a spacer washer (nylon) that limits the travel of the front pulley. Removing this will add 10mph to the top speed.
However, the catalytic exhaust and the air bleed system into it reducing emissions is an integrated system, which means that changing the exhaust requires removing the air bleed system as well.
In the carb mouth in the air filter hose mounting flange there is a brass plate with several 7mm holes drilled into it. I cannot make up my mind if this is a restrictive or emission orientated item. The area of the holes works out at 17mm. The carb is 17.5mm but a 12mm carb will give 5bhp on older standard motors, so removal will affect carb jetting (too much air) and may spoil the way the catalyst works. The catalyst exhaust has a very small resonant pipe around 3.5 inches long. Again, I’m not sure if that is to make the air bleed pulse system through the reed work or not, as the air into the exhaust system front pipe is not pumped but sucked through by the exhaust chamber pulses working through the reed valve in the pipework.
If the exhaust is going to be changed then removing the brass plate is not going to affect the then non-existent catalyst and air bleed system. This will require a much larger main jet, and the new exhaust will need roller weight alterations to suit the new operating RPM.
Size 50 is the standard main jet - be aware that the needle, atomiser and slide fitted are all different to the 17.5mm carb fitted to other earlier models and used as aftermarket add-ons, so do not use these for jetting comparisons. Start with a main jet of 75 and expect to be close. Adjust according to any modifications that have been made. It will depend on the exhaust used. (Use the standard airbox without modifications.)
Because of the original catalyst exhaust a CO meter will not detect air-fuel mixtures accurately, as the CO is absorbed and burnt by the catalyst, and the system also bleeds in fresh air. So I cannot give any guidance on what jet to use with a catalyst exhaust.
On our Dynojet rolling road the CO reading for the standard engine on full throttle was 1.5% instead of the normal 6 to 6.5%. Yet when the motor was stripped for modification it looked to have been running extremely rich. Experiment at your own peril !!!
Fitting a 70cc or 50cc Cylinder Kit
Having made the decision to fit a 70cc cylinder kit the problems start. Piaggio, in an effort to create anti-tamper, have used a smaller spigot (52mm) on the cylinder compared to the normal 50cc motors (54mm), so the 70cc kits will not fit into the crankcase. The first 10mm into the case on the transmission case half is at a smaller diameter, so only a 52mm spigot will fit.
The case needs to be ground back, which means an engine strip to avoid aluminium finding its way into the crankshaft or main bearings.
The standard motor gives approximately 3.2bhp and 30mph top speed. The gearing is restricted by a spacer washer (nylon) that limits the travel of the front pulley. Removing this will add 10mph to the top speed.
However, the catalytic exhaust and the air bleed system into it reducing emissions is an integrated system, which means that changing the exhaust requires removing the air bleed system as well.
In the carb mouth in the air filter hose mounting flange there is a brass plate with several 7mm holes drilled into it. I cannot make up my mind if this is a restrictive or emission orientated item. The area of the holes works out at 17mm. The carb is 17.5mm but a 12mm carb will give 5bhp on older standard motors, so removal will affect carb jetting (too much air) and may spoil the way the catalyst works. The catalyst exhaust has a very small resonant pipe around 3.5 inches long. Again, I’m not sure if that is to make the air bleed pulse system through the reed work or not, as the air into the exhaust system front pipe is not pumped but sucked through by the exhaust chamber pulses working through the reed valve in the pipework.
If the exhaust is going to be changed then removing the brass plate is not going to affect the then non-
Size 50 is the standard main jet -
Because of the original catalyst exhaust a CO meter will not detect air-
On our Dynojet rolling road the CO reading for the standard engine on full throttle was 1.5% instead of the normal 6 to 6.5%. Yet when the motor was stripped for modification it looked to have been running extremely rich. Experiment at your own peril !!!
Fitting a 70cc or 50cc Cylinder Kit
Having made the decision to fit a 70cc cylinder kit the problems start. Piaggio, in an effort to create anti-
The case needs to be ground back, which means an engine strip to avoid aluminium finding its way into the crankshaft or main bearings.
