Project 49 – 68cc Big Bore Kit – Chinese Two-Stroke Scooter Performance 50cc 70cc

This video shows the results from installing a 70cc (68cc) big bore cylinder kit on Project 49, a Chinese 49cc Minarelli / Jog / 1E40QMB powered scooter. The big bore kit is from Autotech355 on eBay. It’s a cast iron cylinder. Like other sport level kits, it’s very good for everyday street riding. Power increases across the rev range.

The first setup was :

Stock variator & fixed drive face without stock spacer washer
4.5g sliders
Stock rear pulley/torque driver
1,000RPM contra spring
Stock clutch, lightened
Stock clutch springs

The second setup was :

Hoca perfromance variator w/2mm spacers
Modified stock fixed half
6.5g sliders
Stock rear pulley/torque driver
1,000RPM contra spring
Stock clutch, lightened
Stock clutch springs

Main jet remained the same as I used with the stock cylinder (80). I had to lean the idle mixture screw a bit. Needle setting remained the same. Do not assume your jetting won’t change. It usually will. Always tune, never assume. I’d suggest upjetting before ever riding. It’s safer to be rich than lean.

The big bore engine was much easier to tune, thanks to the wide power increase. To me, the big bore kitted engine is much more fun to ride than the more peaky piped stock engine. Peak power is probably similar to the ported stock cylinder w/pipes, but lower RPM power is not.

Get all of the details at http://www.49ccScoot.Com and thank you for watching!


Jack Thomson says:

hey just wondering if one of these would work on this “Kinroad XT-50 Q CDi 50cc Motorcycle” it is four stroke. yours sincerely jack

90GTVert says:

You should check out my forum. Multiple people that are good with scoots are around to help. URL is in the corner of the vid.

The CVT needs to be tuned with the proper roller weights and springs so it stays in the RPM range that your engine works in. Otherwise it’ll either rev above or below your peak output and it won’t run right. Kinda like short shifting or waiting too long to shift in a manual transmission. Airbox is fine. No need to mod that if jetting is correct.

MSJDesign says:

Do a 4 stroke project

marc says:

It’s a 1E40qmb I put a 70cc on it and to fine out it was the rubber seal that wasn’t in the way so I Titanic it 10foot pound’s and stripe it it was the rubber seal that was in the way

Anthony Velikajne says:

Will that cylinder kit fit a pw50

mbahmannz says:

hi there, how do you found big bore kit is from Autotech355 ? is that good kit . do you have to do any mod on it or just straight bolt in ? just about to order in just for normal ride not crazy race, just want to get good takeoff because where i live limit speed most is 50kph ,

tjay ismael says:

what Can I do too this kit to make it hit 70mph. besides a stroker. I don’t want a stroker. if I was to Change the transmission and a new Carb. will it his like 70s. and how do I know if I have a 10mm or 12mm wrist pin without taking apart my bore kit. is there an easier way.

AGJT Productions says:

Is there a way we can communicate? Email or hell i would even text you if i needed too. What all do i need to do with the carb? its allready rejetted.. should i modify the airbox? What do you mean cvt tune? I’m new too all of this.

Mohamed Ali Cherkawi says:

please i have Benelli 49x i want uprade to 70 cc what can i do please i need your answer thank you

90GTVert says:

james bezer (won’t let me reply to you) : I always suggest getting a jet kit in order to ensure that the jet you use is the proper one for YOUR scooter and not just what works for the majority. I’ve seen jet size with a BBK vary from about 70 to 95 with stock airboxes or stock airboxes with the snorkel removed. Most commonly I’d expect 85-90 main jet. sells 10 jet kits for the minarelli engines for about $15.

mbahmannz says:

hi , will the kit improve rmp ? do you think better to upgrade 70cc kit or unrestricted cdi ?
thanks regards

90GTVert says:

@ David Hill : You should put some vids up of that.

90GTVert says:

Autotech355 is a seller on eBay. It’s a good street kit. You have to jet the carburetor and probably change the roller weights so they work with the new cylinder. Shouldn’t require any other modifications to run well on most scoots.

AGJT Productions says:

thanks will do

tjay ismael says:

if I was to put on juss this borekit and a racing exhaust. will it make a big difference in top speed and aCCeleration.

jamie xD says:

0 to 35 is shocking i had a aerox 70 and it did 72 mph and was like a fkn rocket

MSJDesign says:

I wish we lived closer I’d donate one to you. Getting ready to drop a 80cc bore kit into a gy6 50cc case with a ported and polished head, intake and carb. Just waiting on the bore kit.

Anjanette Luna says:


joshydoy says:

try putting/getting a shop to put new rollers in. 🙂

Justin Masters says:

Them damn clutch belts man I wish we could keep them quiet exhaust is fine but the belt rattling is annoying as hell

magicdevil1996 says:

Hi can someone help me, i brought a 70cc big bore kit for my cpi moped engine and i brought a new standard 19mm carb. Every time i rev it over half it keeps trying to cut out and has no power, does anyone know why this happens if you do then comment on my video (thanks). Midi moto 70cc cpi moped engine

deom9 says:

My 50cc did 45 anyway, and all I did was just take off the washer restrictor Yamaha W.H.Y

Snatch19882 says:

Love your video’s ! I also experiment a lot with 2 stroke’s 😉

90GTVert says:

I’d go over the carb and CVT tune first as well as checking squish clearance and compression. With your mods, you should be able to go faster than 41MPH if it’s setup well. Mark your variator with a sharpie from center to outer edge and take a top speed run. Check after and see how much travel you’re getting.


please I have scooter 50 CC engine 1PE40MB and i want upgrade to 70CC please what I can do

marc says:

What was the torque wrench measurements

AGJT Productions says:

i got a hammerhead 50cc 2 stroke, big bored and got a racing exhaust. Top speed 41mph. I want more, all else is stock, what can i do?

Joshua Lee says:

i have a scooter it takes a wile to start but when it dose it only stays at 10mph then cuts out i have cleaned the carb and wd40 nearly every thing i had a nasty shock from it the other day so it has the volts but its nt using them please help

melkerpower says:

And how big carb?

james bezer says:

hi i am about to fit my yamaha jog cv50 with a 70cc big bore kit and i am wondering what jet size i need to change to thanks

David Hill says:

kool videos really enjoy them and they really help i own a tng 150 milano top speed 97 mph ;} no joke

MSJDesign says:

Did it myself. I’m not sure it will make an improvement. These motors are so finicky and no 2 motors are alike. But the heads intake is a lot bigger and is now in alignment with the intake mainifold and carb, (that is to say there’s not an edge for the air to slam into and create turbulence) but well see. Might actually be worst off.

Carsten Lorenzen says:

Keep them coming, i love to watch your videos! 🙂

abel berenguer says:

Hi, great video, I have a sym fiddle version 1 from 1999 I fit a 75cc cylinder kit on can you please let me know if you now what the best size four the Maine jet tank you BERENGUER

MSJDesign says:

So I slapped 100miles on the scooter and was riding it to work the next day and I threw the fly wheel. The key is dust and the shaft is buggered. Top speed is in the 50mph range.

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