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Discussion Starter #1 (Edited)
I know there is a lot of post of upgrades to do but I don’t know what ones actually work and make a difference. I have a 43cc mini pocket bike and can top out at around 33mph. I did a few upgrades like a new clutch, carb, tires, and aluminum pull start. Every thing else is pretty much stock. I have a 7 74 gear ratio, but I don’t really want to mess with that too much. What are some mods and upgrades that aren’t that expensive I can do to get more top end without suffering on the low end.
 

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How are you getting your speed ?....33 mph with a 7/74 gearing [10.571:1 ratio]would make your 43cc awefully modded already with more revs than the crank could handle repetitiously over a prolonged period..[ over 16,700 rpm's]..

You need to get real baseline numbers in order to know where you really stand so you know how effective the mods through your hands and interpretation can and will deliver compared to how it was...

You need to find compression ratio,,,squish numbers,,realtime max unloaded aswell as loaded rpms then do a realtime GPS max speed run......

I already know what the bone stock 43cc belts out as far as horsepower[1.6hp] and the max rpm/speeds you can get....

With a wheel circumference of 18"[6" radius] and a ratio of 10.571:1 max speeds at 16,700 rpm's will only belt out a max speed of like 28mph.......

At a realistic 8000 rpms with same parameters its only 15mph.......

I think youre gonna need a small turbine engine swap............
 

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Discussion Starter #3
I used a gps to measure how fast I was going. I was getting 28 with the old worn out clutch and tire. When I first put the clutch in I was getting 31 mph but recently I hit 33 mph.
 

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I used a gps to measure how fast I was going. I was getting 28 with the old worn out clutch and tire. When I first put the clutch in I was getting 31 mph but recently I hit 33 mph.
IDK which GPS you use but its 100% wrong......Math never lies.......

My phone utilizes Snapdragon GPS...I also use the Verizon network...Its dead on accurate with a brand new Dodge ProMaster Hightop Van that uses a transmission speed sensor aswell as GPS to display speed on two spots on the dashboard...

A cag has a 6.5" rim... multiply that by pi 3.14...Youll get around 20.41" circumference...

To verify:

Take your rear tire and put a chalk mark on the tire and the floor at the same point...

Push the bike forwards until the chalk mark is at the floor again,,,Mark the floor again...

Take a tape measure and measure the distance between marks.....

Thats your circumference in inches............

Then you need a Tachometer.......I use a TrailTech TTO its $25 bux.....

Mount it to your handlebars,,take your phone and record a high speed run...

Review the topend run portion of the video and note its max revs.........

Like you said your gearing is 7tth pinion and 74tth rim sprocket

Divide 7 into 74........You get a 10.571...That means your pinion spins 10.571 times before the rear wheel makes even 1 full revolution on the pavement..IE 10.571:1 ratio

Bone stock 43cc engine loaded max rpm's 8500-9000 rpm's

This is the formula for MPH:

Pi * tire diameter = circumference.

Circumference / 12 = circumference in feet.

Axle teeth / clutch teeth = gear ratio.

Engine RPMs / Gear Ratio = Wheel RPM's

Tire circumference in feet * wRPM = feet per minute.

Feet per minute * 60 = feet per hour.

Feet per hour / 5280 = miles per hour.

Or you can just put your values in the boxes in the link below and have it spit you a number based on the figures.......

Heres some speeds of my stuff...

Stand up scooter...49cc alky engine...13,917 rpm's loaded,,gear ratio 6.2:1,tire circumference 9" X1 rim 38.274" circumference...62mph...

Cag... 6.5" rims,,43cc engine,,12900 rpms loaded ,, 7/47 gearing..37mph
 

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Discussion Starter #5 (Edited)
Thanks, I know what you mean about the gps being wrong, but I do always test the ones I use in a car to verify that it works accurately. I will try to do the math too though and see the results. I use the speedometer 55 start app.
 
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