First of all, you have a 3:1 gearbox, sold on very cheap ebay 4 stroke kits.
You can confirm this by measuring the number of teeth of the sprockets inside the gearbox.
The situation is not totally without hope if you know what
you're doing and are willing to make some changes. You need
to use a 56T rear sprocket. Assuming your drive sprocket is 10T and the gearbox 3:1, your
top speed theoretically will be 32mph, and your torque will be
acceptable. Now to get more power from the HS142F 4 stroke
here's what you have to do:
1.Clean out the hole in the plastic insert under the idle screw with
a 0.010 wire. I used a wire from a wire brush.
2. Drill out the carb jet to 0. 026 inches, more like reaming
with a super mini drill bit. Bought the bits online.
3. Drill several 1/4 inch holes in the plastic carburetor cover.
4. Use a very porous air filter. See link below.
5. Install a flexible 7/8 inch ID exhaust tube, 28.5 inches
long for a proven 18% increase in power.
Check this site for more air filter tips:
Here is our test bike.Santa Barbara, California makes an excellent location to build and test motorized bicycles due to the great beach weather we have year around.This bike is equiped with a 49cc HS 4 stroke engine using the EZM Q-matic gear reduction box.This bike is equiped with a front disc...
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