Phatmoto Pro 125cc 4-speed?

[Ralpho]

I'll throw my pennies at this discussion. The two major issues I see here is the gearing and mounting angle. The pit bike type motors have gearing for a tiny rear wheel, around a fourteen I think. With a 1 down 3 up shift pattern an accidental shift into a lower gear wouldn't be good at all but could be cured possibly with a jack-shaft gear induction with a step up on gearing on a shaft. Also, these engines have oil pumps I'm fairly certain so need to be horizontal like the mopeds have mounted under the frame. A jack-shaft will be needed for a bike frame to center the motor but a purpose built frame with a wide hub would need a smaller rear sprocket for the taller wheel.

 

[Ralpho]

Something like this could work. . Some designs I found online.

 

[Vikingimike01]

The frame you sent a picture of, is actually very similar to how I planned mine. And you are right about the smaller wheel, but I think I'll use a 15" wheel and a smaller front sprocket.

 

[MotoMagz]

Here’s a nice Lifan by Sikk

 

[Vikingimike01]

Holy crap, amazing.

 

[Barnfresh]

Motoped

 

[Motorbike Mike]

The built in jackshaft isn't limited to running power to the left side of the bike. You can easily hit up sbp and/or staton to get a new shaft, better bearings and sealed bearing bottom bracket with the chainring freewheel to make use of a multi-speed rear wheel with motor power. That lifan 79cc lifan should have plenty of torque to accelerate quickly in 1st gear and go at least 40 without engine mods. Only reason it's not geared to go that fast single speed is it would accelerate like a dog, and they need to comply with MaB speed limit laws.

Hey Crazy Dan, my phatmoto came in today and 40mph isn’t happening. Top speed 17. Top speed governor bypassed 28. Just ordered a 40T rear sprocket to replace the 50 and we’ll see how that goes.

 

[Vikingimike01]

Is it 4 stroking at WOT?

 

[Motorbike Mike]

Is it 4 stroking at WOT?

Yes- 79cc WOT with 220# rider.

 

[Vikingimike01]

Oh sorry I got confused for a second.. Governor is obviously for a 4 stroke.. Sorry, can't help much with those.