25cc motor jackshaft transmission

I'm starting on a build with a 25cc 4 cycle weed wacker motor. Of course it had no tranny just a clutched output shaft.

Can I use a jackshaft and a reduction tranny? I don't see whay not from looking at the 4 GT 5:1 belt drive trannys. I worked out some ratios and shaft speeds useing a setup like the Sick jackshaft kits.

It looks like it would work. Is there something I'm missing here? I mean you could run chain direct from the 4 GT 5:1 tranny to the rear wheel. So why not run direct from the motor to a jackshaft ending in a 5:1 reduction and from there down to a double freewheel pedal gear and then back to the rear axel cluster gear????????

Is this little engine not powerful enough? They are used on rear wheel friction drives so whay not like this??

Thanks for any help,

Roy

Well to answer my own question there is this: EZ Motorbike of Lebanon: Welcome to EZ Motorbike of Lebanon

And Youtube is full of guys riding bike powered by little weed whipper motors.

Hey Corgi1,

Thanks for the reply. Thanks for the info.

That's the sort of thing I was sitting here doing. I read some other posts that mentioned using 20:1 final ratio but they were talking about 50cc engines. I'm thinking my 25cc motor will have less torque to begin with and so the ratio would be higher to to keep engine rpm up. One problem is I have no clue where the rpm and torque curves cross for this engine. That's probably the best place to set the crusing speed.

I didn't want to use a roller/friction drive so I was doing the math for two jackshafts and down to the crank gear and back to the rear wheel gears like a Sick shift kit would do.

I ended up with a 28:1 final ratio with the engine at 8000rpm and the bike moving at 22.4 mph. Does that sound right??

Thanks,

Roy