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Sx 125 into 200

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Anyone know if its possible to convert and sx 125 into a 200 if so what will i need.

Can i use a 200 barrel head and piston on my 125 crank.

Does the 200 exhaust system fit the same places as a 125.

I would like to carry on using my crank as its new and i cba to take bottom end apart.

My bike is a 2005 sx 125

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yes you can and there has been much discussion about this here and on ktmtalk. Most conversions are 144's, though.

You will need a 200 crank/rod, jug, head, head stays, pipe and silencer, PV parts, longer cyl studs, piston....

might be better off selling your bike and buying a 200....

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yes you can and there has been much discussion about this here and on ktmtalk. Most conversions are 144's, though.

You will need a 200 crank/rod, jug, head, head stays, pipe and silencer, PV parts, longer cyl studs, piston....

might be better off selling your bike and buying a 200....

I didnt relise i needed that much stuff lol

Id rather keep my sx than sell it and buy a 200.

Was only wanting to do this for a big power increase.

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Il just stay with a 125 and im going ot upgrade to a 300 next year.

Does anyone elses ktm have a slight knock when idling. Mine had a knock at idle and looks like piston was slightly hitting head so ive put 3 base gaskets on and the knock has gone but it hasnt got as much power. Ive heard people put extra base gaskets in to make the engine more reliable.

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What size base gasket did you put in? what was in there? It doesn't have as much "power" because you increased the squish (distance between the top of the piston and head) which decreases compression. You should set X dimension to 0 first then make sure squish is around .030-.035" is normal If not then you could have the head shaved. What piston is in there? Wiseco?

It should have a double ring Vertex

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Ive got 2 thick ones and one thin one not sure what the thicknesses are. Running a single ring mitaka piston (not the best but ive always used them and never had any problems)

My plug is fouling alot lately do you think the lower compression is partly to cause aswell as running rich.

It was knocking before i gave it a rebuild. The old piston has a slight ring around the top from were it must of been hitting.

I dont know anyone else with a sx so cant compare engine noise. It only knocked on idle.

I tryed a new piston and a new thick base gasket and it still knocked.

Its not a very loud knock just a constant tap while idling.

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I don't know much about Mitaka pistons but I assume its a forged piston. Make sure you warm it up well before riding. Gaskets come in many different sizes, .20, .25, .40 .50 and .75mm. If you put in two .50 or .75mm gaskets then your x dimension and squish are way off and could be part of your jetting problem. I would order new gaskets and set your x dimension to 0. Most 125sx bikes run in the .40-.65mm range.

How does your spark plug look? black?

Most KTM guys use vertex or wiseco pistons.

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Yeah i warm it up properly.

I will take some gaskets out tomoz and yeah my spark plug black. If i ride slow with hardly any throttle it will foul it when i try to go again.

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Ive decided to go ahead with the 200 conversion. Will i need the 200 subframe and electrics.

Is any parting a 200 in the uk Private message me if you are.

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The only reason you may want nother subframe is if you want 2 tabs to mount a longer silencer. I believe the 125 only has one mount, correct? A 250/300 subframe will work too.

Edited by gmoss

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So i need...

Barrel

Piston

Crank

Studs

Head

Full exhaust system

Subframe.

Will my pv system and cover fit in the 200 barrel.

What about the ignition system will i need the 200s or will the 125s work.

Will my gearbox and clutch etc handle the power.

Will i need to modify the cases for the 200 head.

Wants to gather as much info as possible before i go ripping my engine apart.

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you will need all the PV parts for the cylinder. If you want low end, you will likely want a 200 PV centrifugal timer also. I am in the process of testing this theory with my bike. Stay tuned to my experimentation thread. I have a PV pictorial and will be adding another PV pictorial soon.

The 125 CDI actually adds some giddyup to the 200, keep it.

Gearbox on both bikes are built the same I believe. The clutch springs may be lighter on the 125.

IF you are a member of ktmtalk, there is a build thread of my 200SX by bluebike125, about a year or so ago. It may help you.

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