FL250 Gearing Help Please

[MIKartDad]

Hi Guys … new here…
Just got a Fl250 in a trade , has a 212 on it
.. Took it out .. top speed was 21mph
I’ve since installed a vm22 carb (tuned to perfection) and a pipe ..

my question is how I should go about the gearing .. because 21mph isn’t going to cut it


It’s a 12T clutch to a 20T on the drive spindle to the reduction box which I have read is 9:1 …

should I go up or down on the 20T ?

 

[Hellion]

Hory shet, is that a 4-stroker? Why yes, yes it is and I’d say way underpowered for the application

 

[Whitetrashrocker]

Smaller rear sprocket will go faster with the low end being compromised.

 

[MIKartDad]

Smaller rear sprocket will go faster with the low end being compromised.

So you’re saying … bring the 20T down to say a 12T so it’s 1:1 with the 9:1 reduction box ?
Am I understanding that correctly?

 

[MIKartDad]

Hory shet, is that a 4-stroker? Why yes, yes it is and I’d say way underpowered for the application

Moves just fine imo … very quick to get to 21mph but that’s it …

 

[MIKartDad]

Moves just fine imo … very quick to get to 21mph but that’s it …

I’ve read I take the 20T / 12T =1.667
Then multiply that by 9:1 9x1.67=15.03

if I’m thinking this out correct ..

If I go with a 12T(rear) / 14T(clutch) =0.857

9 x .857 =7.713 which would be dropping it more than half …

am I following this correctly?

 

[Whitetrashrocker]

That sound about right.

Im not sure about that reduction box but most karts like 6:1

Id grab a few sprockets that fit and play with the ratios till you find the best one.

 

[Sparkwizard]

How tall are the rear tires, and what is the tire pressure?

 

[MIKartDad]

How tall are the rear tires, and what is the tire pressure?

From the ground about 21” … 10psi

 

[Sparkwizard]

I divide the tire height in inches, by 2 and use that as a target for my gear ratio.
21/2 =10.5.
I would shoot for about an 11:1 gear ratio with the low pressure tires. Any smaller numbers would be really tough on your clutch.

Try a 14 or 15 tooth sprocket on your reduction unit.

 

[MIKartDad]

I divide the tire height in inches, by 2 and use that as a target for my gear ratio.
21/2 =10.5.
I would shoot for about an 11:1 gear ratio with the low pressure tires. Any smaller numbers would be really tough on your clutch.

Try a 14 or 15 tooth sprocket on your reduction unit.

So a 15 would put me around 11.25 … ?

 

[Sparkwizard]

So a 15 would put me around 11.25 … ?

That is correct.

 

[MIKartDad]

That is correct.

Ty … should that net me a decent top end ? 40+?

 

[Sparkwizard]

Depends on the torque of the engine, rider weight and terrain.
Impossible for me to guess. It will have less acceleration and more speed than it has now.
With 212 cc and 21 inch ATV low pressure tires, you might NEVER see 40.
Let us know how it turns out.

 

[Denny]

I would get rid of all that hokum on the drive train now and switch to a CVT with a 6:1 ratio. That would get you at or near 40 reliably.

 

[Hellion]

Moves just fine imo … very quick to get to 21mph but that’s it …

I need a demonstration please. Can you post a running video? Love the idea of your setup to replace the old 2-smoker engine.

 

[MIKartDad]

I definitely would .. if I knew how lol

do I have to convert a video or something to post it on here ?
But , she does run pretty good, changed out the main jet and got the carb dialed in , just need a caliper now($150) cuz I’m getting up there in speed now and still haven’t put on the 15T roller gear yet
And also think I’m going to ditch the pedals and go back to the steering wheel throttle

 

[MIKartDad]

https://youtube.com/shorts/bjx_RvoLjPg?si=rd_U2EbbsCl8dy0g

 

[Sparkwizard]

That looks like fun!

 

[MIKartDad]

https://youtube.com/shorts/bjx_RvoLjPg?si=rd_U2EbbsCl8dy0g

See if that works …?

That looks like fun!

video link work ?