4-stroke performance

Mike St

Well-Known Member
Local time
9:28 PM
Jun 16, 2008
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:


Active Member
Local time
8:28 PM
Jun 4, 2019
Hey guys! As you may have seen I built a 4 stroke for my girl to cruise around on, and as you could imagine, it's a bit slow. With a lot of pedaling help and about a half mile, it holds about 25mph flat. Is there a certain website I can buy actual performance mods on? Is there a way to tweak valves/carb on this motor to get more power? What clutch should I get? I know you don't get these to haul ass on, but I would like it to be a BIT quicker.
Please tell me this is due to a cheap clutch, not user error. After a total of around 16-17 miles.


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Sidewinder Jerry

Well-Known Member
Local time
11:28 PM
Mar 14, 2011
Rockwood, TN
I don't know what the total weight is you're moving or if you have steep hill to contend with. With that transmission you should be using a 9:56 drive ratio. This'll give you a reduction of 18.67:1. Your engine only produces 1.6 hp. So with an 18.67:1 reduction and only 1.6 hp you'll have to provide a lot of pedal assist. As for steep hill climbing that'd be way to low of a reduction. If the rider is large the clutch is going to be strained even more. Last of all if you're using a single speed you even at a bigger disadvantage because you don't have multiple ratios to pedal assist with.