Wheelies on a 139qmb gy6 100cc possible?

[gapplebees203]

I was wanting to know if anyone here has been able to get their gy6 139qmb to power wheelie(engine picks the bike up on its own)
With out having to pull/jerk back? An if so whats your/their mopeds set up? Like what all have been done to it? Ive modded mine out a bit, but it will only pick up if im going slow and pull back at the right time when i goose the throttle. Also i can get it to jump up from a stop if i goose it an slightly pick up/pull front up when i goose it. But when im in motion i have to be going like 15 an under an have to jerk/pull back farly hard. Any input guys?

[aeroxbud]

Getting any 50cc based four stroke to power wheelie is going to be a big ask. They just don't make a ton of power.
A short wheel base would be just as important. I know someone who used to wheelie a stock Piaggio zip four stroke for ages.
A Baotian speedy with an 80cc kit used to come up quite easily with a small tug on the bars while accelerating. But 10" wheels and a short wheelbase really help.
So does sitting very far back on the seat.

[snaker]

Got a lot of things going against you.
Most 70 hp motorcycles can't power wheelie, a 7 hp scooter engine doesn't help.
But then, 125cc 2 stroke dirt bikes often can.
For them its probably part a sharp peak power and part chassis design, along with a lot of squatting rear suspension and a push off from the front suspension.

I think the Torque Sensing feature on the CVT is also a factor.
I can imagine it dampening the torque going to the rear.

I recently watched a Moto GP video clip that showed a bike lowering the front suspension (a lot) as a launch control to reduce launching wheelies. I never knew they did that.
I know Motocross bikes can lock in a relatively small amount of front suspension squat for launch, but the Moto GP dropped the front almost to the ground
So raising the front suspension or stiffening it and softening the rear suspension can help, although it will probably make the thing ride like crap.

[gapplebees203]

So this is what ive done to my moped so far, ive put a 52mm bbk an bvh, A9 cam, 28mm pwk carb, performance exhaust(1"? A Guess), performance front variator(I cant remember wieghts I used), 2k clutch springs, 1k compression spring. Intake is still stock Rpms usually run about 5200 @ 50+mph 4k @ 30mph. Take off is farily quick. An will go up hills at 40+.
Ive been thining about replacing the intake an porting my head to a degree where air isnt being restriced from the drastic change from 28mm @ carb, to 17mm cylinder head. Wanting to widen it out some.

[90GTVert]

Keep the wheelbase short as others have said. Raising the center of gravity may help. My understanding is that you think of the distance from the rear tire's contact patch to the center of gravity as a lever. The higher the center of gravity, the longer that lever is and the more likely you are to wheelie. This is why drag bikes are low, or part of it anyway.

A friend has the same engine as me for the most part. My high scoot will wheelie like crazy at low speeds (~25HP two-stroke). He put his engine in a long low scoot and it will not wheelie. His problem became traction. The scoot in your avatar is short and relatively tall, so you're starting off well.

I think the problems you'll have are the amount of power available and how hard you can make it hit. The two-stroke racing stuff is comparatively ridiculous. Lots of power and they jump right to peak power thanks to the over range racing CVT setups and high end clutches that are available for them. Some 150s feel like they are close to being able to lift the front wheel a little. I'd expect something like a 150 in a similar frame to be a better choice... but really I'd go for a two-stroke if I wanted power wheelies. More power, more wheelies. Swap an RC-One into that frame and good luck hanging onto it. I had a very mild 90cc 2T in a retro short wheelbase scoot once and even that thing would wheelie pretty easily at low speed.

You can also employ a sort of bounce technique if you're close to getting the wheel up. Getting into it so it raises and then out of the throttle. Catching it as the front suspension is rebounding gives a boost in lift.

[gapplebees203]

Feb 2, 2024 8:29:51 GMT -5 90GTVert said:

Keep the wheelbase short as others have said. Raising the center of gravity may help. My understanding is that you think of the distance from the rear tire's contact patch to the center of gravity as a lever. The higher the center of gravity, the longer that lever is and the more likely you are to wheelie. This is why drag bikes are low, or part of it anyway.

A friend has the same engine as me for the most part. My high scoot will wheelie like crazy at low speeds (~25HP two-stroke). He put his engine in a long low scoot and it will not wheelie. His problem became traction. The scoot in your avatar is short and relatively tall, so you're starting off well.

I think the problems you'll have are the amount of power available and how hard you can make it hit. The two-stroke racing stuff is comparatively ridiculous. Lots of power and they jump right to peak power thanks to the over range racing CVT setups and high end clutches that are available for them. Some 150s feel like they are close to being able to lift the front wheel a little. I'd expect something like a 150 in a similar frame to be a better choice... but really I'd go for a two-stroke if I wanted power wheelies. More power, more wheelies. Swap an RC-One into that frame and good luck hanging onto it. I had a very mild 90cc 2T in a retro short wheelbase scoot once and even that thing would wheelie pretty easily at low speed.

You can also employ a sort of bounce technique if you're close to getting the wheel up. Getting into it so it raises and then out of the throttle. Catching it as the front suspension is rebounding gives a boost in lift.

Thanks for the pointer, looks like ima have to break out the white board an make a rocket science equation for this issue.
Also is their any other things i can do to this engine to squeze out as much power as i can? Im thinking my next step will be to tackling this cvt. Is their a proven rear clutch pulley better then a srock one out their for the 139qmb? I know the mods for these are vary limited due to demand, cause the 2 strokes claim this game. Honestly im wanting it to produce anough power to race more then to show off an play around doing wheelies. The way i look at it, if it can wheelie on its own, i have some torque to trade in for top end speed while maintaining take off speed. But on the other hand, id still would like it to be able to do both, even if i have to help it get the front end off the ground for wheelies.
Id like this thing to take some 2 strokers out to eat at gapplebees im a believer that anything is possible. So when someone says it cant be done, just motivates me even more to prove em wrong.
Might i mention my rpms are barly beimg tapped into on this thing, i read that people are going 55 @ 6500-9000 rpms on flats on these, while ive got mine to go 50 uphill at 5k rpms. So if i much raise my rpms up more it shall be.

[90GTVert]

First thing I'd do in your shoes is tune the CVT with sliders and make sure the clutch has the springs that work best in it. Sometimes with these big 139QMBs the RPM is a tradeoff of performance vs longevity. Seems like people keep RPM down to stress them less. For me, if I've got to go big on parts then I've got to see what they are capable of without restricting them with heavy weights. Best way to find out what gives you strong acceleration is to do acceleration tests back to back with different weights and springs, one change at a time. If you're serious about it, a dragy is well worth the money to have reliable timing that's very simple to use. Love mine.

amzn.to/4bi9i3r


Here's a source for some quality CVT parts. Malossi and Polini would be my choices where available. They have a Naraku torque driver. NCY also makes one, but it's not sold there. Straight groove is usually good for acceleration.

www.scootertuning.ca/en/7000-gy6-50cc-139qmb

[gapplebees203]

Thanks 90GTVert! That parts site seams nice, checked it out. Theirs some nice parts in their. Will have to order me a new exhaust when i can, also been interested in replacing my crank, got any sugestions on what i should chose? Also do you know the differance in the tooth counts on them? Looking for some better then stock bearings to handle the higher rpms better, also is that dragy just a gps track timer? Or what?

[90GTVert]

Sorry for the late reply...

The dragy is basically just a GPS device that works at a higher frequency than phones do so it can be more accurate for acceleration tests. Works really well though. I've tested it vs track timing and it's really close... but the dragy gives more info than the track timing equipment does. There are others out there now, but I haven't talked to anyone with a dragy that doesn't like it.

I would use a "racing" crank to get something made to higher standards. Tooth count is for the oil pump drive :
49ccscoot.proboards.com/thread/16279/gy6-16-tooth-22-crank