Looking to limit top speed on 80cc motorized bicycle

Acton67

New Member
Jan 17, 2020
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Hey guys,

I bought one of these kits recently for my 12 year old nephew whose been struggling with depression. I wanted to get him out of the house and teach him a thing or two about mechanics and two strokes in the process. I bought the Goplus 80cc motorized bicycle kit with a few other upgrades based on what I read would be good ideas to improve performance and safety. I bought an aftermarket carb with the offset intake manifold, a CNC sprocket adapter, an aftermarket chain tensioner, 2 shimano caliper brakes with a dual brake lever, a double leg kickstand, and an aftermarket NGK sparkplug.

The CNC sprocket adapter came with a 36 tooth sprocket which I definitely DO NOT want to use right off the bat. This is a build for my 12 year old nephew. He has a good head on his shoulders and at this point in his life I want him to start getting out into the world and enjoying what life has to offer. His father (my uncle-in-law) is all for the idea, but since I'm primary the one doing all the research on this project I'm responsible for making sure the build is safe.

I'm thinking of getting a higher tooth sprocket that will further decrease the top end speed, the 36 tooth sprocket increases top end speed past what the stock sprocket already allows for, but I'm not sure the stock sprocket is compatible with the CNC sprocket adapter. Can anyone recommend any mods I can do to limit the top speed to 15-20mph MAX? Any other suggestions for a young rider like this?

Kids need to get out and live more and experience the world! If the kid gets a few scrapes falling off his bike but has a smile on his face doing it, he'd be way better off then he is now! I just don't want him to get seriously hurt and I didn't realize how fast these bikes can go even without any serious mods right out of the box.
 
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Greg58

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May 1, 2011
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Welcome Acton, the largest sprocket I've seen that won't break the bank is a 44T for a hub adapter. Most sprockets from eBay vendors have both mounting holes patterns. Even if you could find a 48T or even a 56T the bike would still do 25mph with ease.
 
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bairdco

a guy who makes cool bikes
Aug 18, 2009
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There's some simple mods you can do to slow it down.

Decrease the intake opening. Easiest way is to cut a gasket for the intake manifold and make the hole smaller. Or make a thin sheet metal restrictor plate with a smaller opening. Make sure you have a gasket on both sides.

A larger sprocket will slow down top speed, but I've had well tuned bikes with no mods and a 44t that would do 40mph.

But you might get "lucky," and have a crap engine that's slow right outta the box. : )
 

Acton67

New Member
Jan 17, 2020
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Personally I hate using 'em, but here's a thumb throttle with an adjustable governor that should work. They're really better for beginners. If they panic a little it's easier to release a thumb than to twist a throttle forward.

https://www.amazon.com/GOOFIT-Universal-Throttle-Control-Assembly/dp/B00ZWZUF44
This just got me thinking, is there anyway to restrict the throttle grip itself from being opened up all the way? Like can I make the grip stop turning at halfway open?
 

BlindAngel

New Member
Oct 7, 2016
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Keep in mind that in most states probably all of them you can't ride on the road unless you are over 16 so he'll have to keep off the road.
 

Tony01

Well-Known Member
Nov 28, 2012
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Yeah these things go about 30. As said above there are simple ways to make it slower. Unfortunately they’re illegal to ride on the streets without a valid license.
 
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BlindAngel

New Member
Oct 7, 2016
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Here's a link to a 56tooth sprocket, a word of caution though the higher the teeth the more torque the bike will have so unless the kid weighs like 200 pounds it's quite possible that the bike will wheelie and that can be just as dangerous on one of these as speed is. Make sure for the kids sake he has a decent helmet and preferably some crash gear as well.

https://www.amazon.com/CDHPOWER-Mul...?keywords=80cc+sprocket&qid=1580051225&sr=8-4