CNS Carburetor for Motorized Bicycles

The CNS carburetor kit includes a handlebar mounted choke lever and choke cable, K&N style cone air filter, throttle cable, throttle assembly, offset longer intake manifold to clear frame, and fuel line.

Comparing Carburetors- The CNS carburetor for 2-cycle bike engines is a performance booster over the normal NT carburetor. The New Style 66cc carburetor designed for SkyHawk engines is also a performance booster compared to the normal NT carburetor which was originally designed solely for 48cc engines. Upon initial installation of the CNS, you may not see much of a difference compared to your old carb.

The benefit of the CNS carb can be realized several ways.

The 2-cycle bike engine is a scavenging motor design meaning that fresh and spent fuel charges are circulated throughout the engine during the normal combustion process via the cylinder ports which connect the upper combustion chamber to the lower engine case and crankshaft. Fresh air/fuel charges enter the cylinder from the carburetor and intake manifold straight into the lower engine case. The fresh charge then swirls around the lower bearings providing needed lubrication and then enters up the side channels of the cylinder ports into the combustion chamber. Some of the burnt exhaust charge escapes through the muffler and some recirculates down through the cylinder ports to re-lubricate the lower engine bearings.

At low RPM and low throttle, the engine receives adequate lubrication. At high RPM and full throttle, the fresh charge quickly explodes in the combustion chamber and rapidly exits the engine not leaving enough time for the oil that is mixed into the gasoline to lubricate the engine bearings or cylinder wall and piston. This partially explains why smoke is more likely to be visible at the exhaust during idle compared to full throttle. (Side note - not all visible smoke particles are harmful to the environment. Consult your local emissions testing station for more information.)

Because the CNS carb has an air/fuel screw (turn in to close the air channel and make richer, open to make leaner) and an idle screw, it is possible to tune the carburetor to suit your individual style of riding. If you consistently are trying to reach top speeds and high rpm, then you will benefit from owning the CNS carb and the ability to richen the air/fuel ratio.

The other added benefit of the CNS carb is that the main jet is larger than stock and the jet needle has a more precise taper, meaning better throttle response. The inlet and outlet ports on the mouth of the carb are much larger and require a 2mm thick nylon shim in order to be adapted to the stock intake manifold (supplied in the kit). The normal aspiration of the engine is blocked.The air/fuel flow is not restricted by the carburetor on a stock engine, but rather by the poor port castings from the factory. If you were to use a dremel to open the cylinder, intake, and exhaust ports you would then find the real benefit of the CNS carburetor. In that instance, it will supply a larger amount of fuel and deliver what you need from a real carburetor.

Ports on the CNS carburetor-
The pink tube that comes attached to the carb out of the box can be disregarded. The port tubes are for various purposes. One port tube is for equalizing pressure in the float bowl, and another is a vacuum.

Adjusting the carb-
The front screw is for the idle, the rear screw is for air/fuel. Set the idle to a good speed. Then "blip" the throttle and listen to how long it takes for the idle to return back to normal. Adjust the air/fuel screw so that mix just gets rid of the lingering idle. Run the bike for a while and pull the spark plug to check the condition. If the plug is dry, tan or white then you should turn the air/fuel screw in so that you richen the mixture. This will help keep your engine cool and well lubricated, especially at higher rpms. 

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