DRIVE RATIO PROBLEM IN AUSTRALIA...

[GREGSKI]

Need some help please, I Purchased FL250 with a new 4 stroke motor , unmounted. thats all there was, i took it as it was a project for my son and I.
Fitted a centrifugal clutch with 17T sprocket - to output shaft on 15HP motor. Motor is good for 4000 rpm, but thats it.
I then fitted 13T on input shaft of gearbox, the gearbox is a 9.5:1 reduction to the wheels.
Runs well at top end but struggles on take off; Burnt one set of springs already.
Obviously 13T sprocket too small, but without knowing the original ratio between the two pulleys i am only guessing.
could someone please help me out with diameter of both pulleys.
also did the original FL250 come out with variable speed drive??
many thanks

[LiveWire]

The FL250 came with a with a variable belt system. At full shift out, it was probably around. 8:1. So you have a ratio slightly higher than the highest gear of the original setup. What is the size of the output shaft of your engine?

[GREGSKI]

Engine output shaft is 1" its a standard motor 15.5hp to be exact.
either way i seem to be in a fix
if i leave the clutch & 17t on motor, and upsize from 13t to 25t on gearbox input shaft.
i may get the better take off, but top speed will be approx 28km/hr.
it may just have to be trial and error.
thanks

[LiveWire]

I can get you a clutch similar to the factory drive clutch which will fit that engine. Do you still have the driven clutch off the chain case? That would give you a variable ratio. 15.5HP is not much less than the stock engine and the 4 stroke likely has more torque. So with a variable belt drive, performance could be similar to stock.

[GREGSKI]

Thanks for the offer, but i did some tweaking around on the weekend
i did put the 25T sprocket on the gearbox input shaft, left the 17T clutch on motor shaft
and the oddyssey has turned into a hill climbing monster. very happy with the 8:1 advice you gave many.
top speed is fast enough to frighten anyone.
many thanks.