How to Increase the Power of the 48cc Engine of Motorized
Without modifications this engine only has 2 horsepower and is not strong enough to easily haul heavy people or climb the inclined streets which are common here in Cuenca. This page lists the necessary modifications to make it where you can climb most streets up to around 10 degrees inclination.
Reduce the hole diameter in the carburetors main jet to .6mm to maintain the ideal ratio of air to gasoline (15 to 1) in this high atmosphere where the air is less dense. (look at this chart). Less gasoline in places of high altitude surprisingly gives more engine power (and around 80km per tank which is 1/2 gallon).
Install an extension (10-14cm) between the carburetor and the motor which makes use of vacuum/pressure wave resonance to push 15% more air/gas mixture into the engine for 15% more power when your speed is less than 15mph. This is very important if you want to be able to climb inclined streets.
Cut 1.5mm from the bottom of the intake skirt
of the piston to permit the air/gas mixture to enter the engine 4 degrees
earlier in each engine cycle. The period of intake port opening will then
be 121 degrees as this chart shows is the best for both low and high
rpm's. Or if you want the best climbing power and don't care about losing
1-2mph in top speed then cut the skirt 2mm for an intake period of 125
The engine compression of air/gas is less in places of high altitude and needs to be corrected by reducing the compressed combustion area. This can be done by not using the head gasket. But to prevent any compression leaks both mating surfaces need to be leveled by moving them in a circular pattern on sandpaper on glass. Also you can increase the compression even more by having the head mating surface milled down by .5mm.
Use a rotary tool to change the ports in the cylinder to be equal to the measurements in the drawing below. This will increase power throughout the whole rpm range.
References: "The Effect of Crankcase Volume and the Inlet System on the Delivery Ratio of Two-Stroke Cycle Engine" by Fujio Nagao of the University of Kyoto
Motorized Bicycles are available from the business "Auto Comercio" on Avenida de las Americas (east of Super Maxi) in Cuenca. Call Esteban Mogrovejo at 080-718-421. They charge $250 to install the engine kit on your bicycle, or $400 for a complete motorized bicycle.