How to make a 50cc faster on the cheap
Based on a Jincheng 50cc but may also apply to others. If your too skint to bore up or you simply would like to see what you can get out of your 50 on the cheap then this may be of use to you.
Modding the inlet manifold:
Remove the inlet manifold and note the small (6mm?) hole at the head end. Use a piece of thin cardboard to make a template of the size of the inlet in the head. Lineup the template on the manifold and use paint or a marker to mark the material to be removed. Then using a rotary burr in a dremel or similar open up the manifold to match the head, tidy it up with a small grindstone or sandpaper wheel.
Now move onto modding the airfilter, cut off a section of the rear of the filter housing to remove the restrictive long thin inlet pipe. Open the filter and remove the plastic disk from the wire gauze section, bend any ends of wires you break so they point away from the foam.
If your unlucky after the above mods you may find that the fuel just can't get into the float bowl quick enough. The bike will start to splutter and die after a few minutes riding. First check the flow from the hose to the carb to make sure there’s no blockage there. Then you need to remove the carb, remove the float bowl and then reconnect the fuel line and test the float operation. If with the float down the fuel just slowly drips then you need to drill out the inlet hole that the float valve operates in untill you get a slow but steady stream or at least a fast drip. Be very careful to keep the hole neat and straight and don't go too large or the valve wont seal. To help it seal use a larger bit by hand to neaten up the hole and very slightly taper it's edges.
This gave mine 45mph on the flat with a 11 1/2 stone rider, and the best bit is it didn't cost a penny.
If you have a restricted CDI you'll also need to replace it, all the dealers stock them or a c90 one can be used. I'm not sure how to identify a restricted CDI, I think all the large square ones are restricted but I'm not sure if any of the normal sized rectangular ones are. I have a C90 one that I havent got round to trying yet.
Stopping from 50 down hill on a wet bumpy road with standard rear shocks and original nobly tyres aint fun though so it's now probably time to part with some cash.