ktm sx from 125 to 150cc

hi there im intrested to convert my 125sx to a 150sx

i know that i basically need a piston,cylinder,head and cranshaft with rod...

so the cost is not tinny...

im thinking to save some money with using a 125 cylinder bored and replated

can this been done? im thinking i spend half of the money of an new cylinder...

is that possible?

Sadly not, you need a cylinder. The clinder walls are too thin.

Ohh and it's a 144cc.

tye1138  a friend just picked on a nice 07 125.  He too is looking to convert it to a 144 when its due for a top end.  What years are candidates for the bolt on 144 kit?  He understands he'll need the complete top end, including cylinder, power valve, piston, rings, head, etc.  I just want to confirm that his 07 is a good candidate to upgrade.



Edited by eprovenzano

The bottom end hasn't had much change since 2003, so it really doesn't make a difference which year since you will be replacing the crank, cylinder, piston, head, etc.

The best parts to get for the 144cc upgrade are the 2010+ components. It seems KTM hasn't made very many MAJOR changes since that motor. So when I did my upgrade, I bought a 2009 cylinder (which hadn't been changed) and a 2010 head/crank. The pistons have gone through many revisions, but the Vertex is by far the way to go.

The last thing you'll need is a 150SX cdi. I found it makes a HUGE difference in the power delivery. I tried to get by with a 07 144 CDI and it didn't work, neither did my 07 125 CDI. So I actually splurged and bought a new one. To my utter surprise, the 2010 150SX CDI I bought made a HUGE difference and I haven't looked back. Mind you... I was running a 144SX 39mm carb, so perhaps with the stock 125 38mm carb, things are different? I know the jetting is totally different between the two carbs.

Anyway, I personally wouldn't bother upgrading a motor unless it already needs a lot of work. Its far cheaper to buy a used 150SX motor and get the CDI as well...

Ohh and the 144cc machines seem to love the FMF 125 resonator with short silencer. Go figure!

Thanks for the info, I'll pass it along.  

so i need the same parts for a 150 or 200 conversion?

i was willing to do a 150 conversion cause i did'nt wat to spend alot of money for a 200 upgrade...

but i see that both conversions are about the same...

ether for a 150 or a 200 conversion  need about the same parts...

piston,cylinder,crankshaft assembly,rejeting and a cdi

so if the parts of the 150 and 200 cost the same(whitch they dosent)the upgrade costs the same money


so i need the same parts for a 150 or 200 conversion?

I think there is an easier way of doing it. I know KTM had an upgrade kit for the 125 and I'm not sure if it included a crank/rod. You'll have to wait and see if one of the 200 experts posts on here.

i said that because if you have the budjet you can go 150 or 200cc with the same money

i want to make mine 150cc because i want to trailride not doing only mx...

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