Top Speed

[Chainlube]

I have 50 cc version in my shop, 3 speed full of oil and carb on it and it weighs 39.4 lbs.

 

[Anime2019Master]

My current top speed is about 35mph on level ground. Upgrades are high compression head, mz65 generic muffler, 38t sprocket, ngk plug and upgraded ngk cdi wire, and rejetted to 65mm. I could get about 40mph if i dropped the gearing to a 36t but theres alot of hills where im at, so i need at least some ability to tackle them, lol. I also plan to upgrade the cdi eventually as well, but while thatll give better, more reliable spark, i dont see it likely to boost speed much.

 

[Street Ryderz]

My current top speed is about 35mph on level ground. Upgrades are high compression head, mz65 generic muffler, 38t sprocket, ngk plug and upgraded ngk cdi wire, and rejetted to 65mm. I could get about 40mph if i dropped the gearing to a 36t but theres alot of hills where im at, so i need at least some ability to tackle them, lol. I also plan to upgrade the cdi eventually as well, but while thatll give better, more reliable spark, i dont see it likely to boost speed much.

The 38t sprocket is limiting you're speed and if you were to put a 36t chances are you'll go slower or just take longer to get there! These engines in their stock form or modified have a sweet spot where they like to run best and stock like yours is usually between 6.5 and 7.5 k not a very big range but they can run all day there when setup right. You can use your gearing to set top speed or to get a good cruising speed and retain the engine life a stock gear 44t on a 26" wheel at 7k gives you around 30 mph and another 10 at top speed easily without over revving the engine and a better over all pull,or if you really want to get a good top speed the engine can be reworked/modified to handle more rpm and make more torque to turn the smaller gears but without this work the engine just struggles to over come the load of the smaller gears and ends up going slower.

 

[5-7HEAVEN]

That 60t is 9.55” diameter.

The 48t is 7.64” diameter.

 

[Anime2019Master]

The 38t sprocket is limiting you're speed and if you were to put a 36t chances are you'll go slower or just take longer to get there! These engines in their stock form or modified have a sweet spot where they like to run best and stock like yours is usually between 6.5 and 7.5 k not a very big range but they can run all day there when setup right. You can use your gearing to set top speed or to get a good cruising speed and retain the engine life a stock gear 44t on a 26" wheel at 7k gives you around 30 mph and another 10 at top speed easily without over revving the engine and a better over all pull,or if you really want to get a good top speed the engine can be reworked/modified to handle more rpm and make more torque to turn the smaller gears but without this work the engine just struggles to over come the load of the smaller gears and ends up going slower.

This is my second build, on my first build i have a 36t sprocket. It does indeed take longer to get to top speed, but by no means will it be faster than a 44t. No chance. Top speed on that one is 42mph, cruising speed of 38 on flat, though i got it up to 49mph once, (cheated, used a hill.) I was getting 28mph top for current build, with 44t, replace it for 38t and now i have 35mph top. I agree that the 44t would be better option if the engine is stock, but mine is far from it, the expansion chamber alone helps greatly to get back some of the low end torque lost from a smaller sprocket. Soon ill replace the jug and piston with ported versions as well. Although, to be clear, i have no intention to put the 36t on this build. Too many hills. Currently i get decent climbing ability, as well as getting up to top speed fairly quickly. (4-8 seconds), so torque is acceptable for my needs. Certainly better than my first build by far. Ive put what i learned there to make this one better, currently im up to about $800 invested in this build. I didnt buy a walmart special like my first build to put the engine on, i bought the frame, wheels, front fork, and gearing seperate to byild this completely from scratch.

I do also have a runtong hp carb, but even with rejetting i was getting crap power with it, lost 8mph+ and a lot of torque with it compared to the standard nt carb. I intend to switch it out for a speed carb eventually, basically the same as the nt, but with the scoop it gets better airflow.

 

[Street Ryderz]

This is my second build, on my first build i have a 36t sprocket. It does indeed take longer to get to top speed, but by no means will it be faster than a 44t. No chance. Top speed on that one is 42mph, cruising speed of 38 on flat, though i got it up to 49mph once, (cheated, used a hill.) I was getting 28mph top for current build, with 44t, replace it for 38t and now i have 35mph top. I agree that the 44t would be better option if the engine is stock, but mine is far from it, the expansion chamber alone helps greatly to get back some of the low end torque lost from a smaller sprocket. Soon ill replace the jug and piston with ported versions as well. Although, to be clear, i have no intention to put the 36t on this build. Too many hills. Currently i get decent climbing ability, as well as getting up to top speed fairly quickly. (4-8 seconds), so torque is acceptable for my needs. Certainly better than my first build by far. Ive put what i learned there to make this one better, currently im up to about $800 invested in this build. I didnt buy a walmart special like my first build to put the engine on, i bought the frame, wheels, front fork, and gearing seperate to byild this completely from scratch.
View attachment 101298
View attachment 101299View attachment 101300

I do also have a runtong hp carb, but even with rejetting i was getting crap power with it, lost 8mph+ and a lot of torque with it compared to the standard nt carb. I intend to switch it out for a speed carb eventually, basically the same as the nt, but with the scoop it gets better airflow.

Trust that I know what I'm saying since I've built literally over 1000 of these bikes in the 17 years that I've been playing with these now,it was 18 years ago when I first got a bicycle engine and I spent the first year pushing the crap out of them to see what they could do and grenaded around 8 engines before finding what really worked. You're engine is stock it's not ported the crank isn't balanced it still uses the factory cdi and so on, the head is not higher comp and unless you decked the cylinder and set the proper squish clearance it does nothing but aid in cooling and resist warping. That pipe is slightly better than stock but that's it there is no real boost or defined power band it just breaths a bit better, as for the carb the speed carb is just slightly bigger than the regular nt but it's filter cover does not scoop in air that's not how a carb works on a 2 stroke. As for you're gearing again that's not right since a stock engine with the proper gearing (40-44 t) can easily hit 40 mph when setup right, they can also go faster still as I've hit 50 all stock with a stock Bertha pipe that does nothing but allow the engine to breath there is no pipe hit to it it's all engine doing the work.
You will find alot of good info within these pages to help you achieve you're goals and many experienced people whom have been there done that and are willing to help if you're willing to listen and learn!

 

[Anime2019Master]

Trust that I know what I'm saying since I've built literally over 1000 of these bikes in the 17 years that I've been playing with these now,it was 18 years ago when I first got a bicycle engine and I spent the first year pushing the crap out of them to see what they could do and grenaded around 8 engines before finding what really worked. You're engine is stock it's not ported the crank isn't balanced it still uses the factory cdi and so on, the head is not higher comp and unless you decked the cylinder and set the proper squish clearance it does nothing but aid in cooling and resist warping. That pipe is slightly better than stock but that's it there is no real boost or defined power band it just breaths a bit better, as for the carb the speed carb is just slightly bigger than the regular nt but it's filter cover does not scoop in air that's not how a carb works on a 2 stroke. As for you're gearing again that's not right since a stock engine with the proper gearing (40-44 t) can easily hit 40 mph when setup right, they can also go faster still as I've hit 50 all stock with a stock Bertha pipe that does nothing but allow the engine to breath there is no pipe hit to it it's all engine doing the work.
You will find alot of good info within these pages to help you achieve you're goals and many experienced people whom have been there done that and are willing to help if you're willing to listen and learn!

I do plan to get a ported jug and piston soon, dont trust myself not to do it wrong, so ill buy one. And already ordered a better cdi a few days ago, just havent arrived yet. Ill take your words for it tho, i cant afford to build a bunch of these, so obviously youd have a wider range of knowledge. But i do wonder, what am i doing wrong with the 38t, if i put the 44t on it, changing nothing else, i lose 7mph compared to the 38t. Perhaps once i have the ported jug and cylinder? Or would it be the better cdi that would make up the difference. I do have a ngk plug, if thats relevant. Its hard to imagine these little engines going much over 30-35 max with 44t, mustless 40+.
Edit: also how would i balance the crank? I wasnt aware this could be done, i assumed you had to buy a low end pre balanced.

 

[Chainlube]

I do plan to get a ported jug and piston soon, dont trust myself not to do it wrong, so ill buy one. And already ordered a better cdi a few days ago, just havent arrived yet. Ill take your words for it tho, i cant afford to build a bunch of these, so obviously youd have a wider range of knowledge. But i do wonder, what am i doing wrong with the 38t, if i put the 44t on it, changing nothing else, i lose 7mph compared to the 38t. Perhaps once i have the ported jug and cylinder? Or would it be the better cdi that would make up the difference. I do have a ngk plug, if thats relevant. Its hard to imagine these little engines going much over 30-35 max with 44t, mustless 40+.
Edit: also how would i balance the crank? I wasnt aware this could be done, i assumed you had to buy a low end pre balanced.

If you look through these pages, https://motoredbikes.com/threads/breaking-down-a-china-ht-engine-in-pictures.23495/ it gives you the complete break down of the engine. You have to be willing to take one apart and do a little work on it to get it balanced. To balance a crank you have to take metal from the piston side, which is equivalent to the weight of the piston and rod. Search around on this site, it has all been covered.

 

[Street Ryderz]

I do plan to get a ported jug and piston soon, dont trust myself not to do it wrong, so ill buy one. And already ordered a better cdi a few days ago, just havent arrived yet. Ill take your words for it tho, i cant afford to build a bunch of these, so obviously youd have a wider range of knowledge. But i do wonder, what am i doing wrong with the 38t, if i put the 44t on it, changing nothing else, i lose 7mph compared to the 38t. Perhaps once i have the ported jug and cylinder? Or would it be the better cdi that would make up the difference. I do have a ngk plug, if thats relevant. Its hard to imagine these little engines going much over 30-35 max with 44t, mustless 40+.
Edit: also how would i balance the crank? I wasnt aware this could be done, i assumed you had to buy a low end pre balanced.

Setup is key to getting the most from the engine, the load from a smaller gear is harder for a stock engine to over come and make use of the potential rpm so you could be jetted too lean or have an air leak that will rob a lot of power,the video I put above is a stock engine with the speed carb and it's operating at 500 -1100 ft above sea level it's jetted with a # 70 jet to get as much fuel as possible without 4 stroking under load it's a little bit rich and you can hear it in the video when the throttle is let off but this ensures no heat issues and yields the most power for that setup, it is running a 40t gear and 26" wheels with tires that make it 27+ " in dia which adds to the circumference and makes turning any smaller than that gear harder on the engine to get up to peak rpm. I have a video on this site explaining how we balance the crank to shift the rpm peak up and keep it smoother in that range.The cdi if it has a lower base timing and less advance as rpm climb also helps to keep it smoother plus helps to get a better burn of more fuel with a stronger spark which will then make a bit more power. With the 44t gear and 26" wheel 10k rpm is around 42 mph and can be done with all stock components pretty easily as I've shown, going above 11k rpm is where you will run into problems if the engine is not prepped properly and even still I don't like to go above that for fear of failure at that speed which is no fun!
So if you work on you're setup and get it to unload a bigger (stock) gear properly you should go a bit faster and have a better pull doing it. I suggest some reading and trail an error with the tuning until you get where you want to be as for many of us here that's half the fun!

 

[Street Ryderz]

This isn't top speed for the setup but shows the time taken to accelerate from 20 to 40 mph using the gps race timer app, it's funny to see peoples claims of how long it takes to reach top speed being ridiculously low! Most of us realize that these engines don\t start to pull hard right out of the hole because the port timing hasn't kicked in yet and that's why these test is preformed from 20-40 I only hit 50 in this run as a top speed after the timer stopped it was still accelerating and I lifted off the throttle, still to this day it is the fastest acceleration time from a china girl with all Chinese parts not a saw cylinder or Minarelli hybrid as they have posted some impressive times.