ktm 125

[pete 2]

i know the 125 ktm is a fast bike,but is there any porting changes needed to improve or enhance it.

 

[pete 2]

Also is it setup to run unleaded? any benefit using leaded and what changes are needed?.

 

[marcusgunby]

what year kTM?

 

[pete 2]

2004

 

[pete 2]

Sorry,is there a difference in the model years?its a friend who i help out,not sure which year,but it will be at least from 2002 up.

 

[marcusgunby]

The 02 i feel had a good spread of power, the 03,04 seem a bit weak on revving out, they do rev but make most power low and mid.I would look at more top end power with porting on the 03,04.

 

[Jman271]

There is some power to be had on the 03-04 for sure! There are a few mods you can do to the PV flapper as well as the subs and cyl base that will make that bike pull and rev big time!

 

[marcusgunby]

Jman tell me more as a friend has a 05(same engine as 04) and i think it needs more rev.

 

[pete 2]

marcus,thanks for the replies,
jman,thank you also and if you guys dont mind could you explain a bit more about these mods.

 

[Jman271]

Some, (everyone I have worked on) of the large PV flappers don't open all the way when the actuator arm is all the way in the up position. KTM has this "Z" dimension that they spec in the book as the correct height of the PV flapper from the top of the jug. On the 125's it is about 43mm. This measurement makes no sense if the pv flapper doesn't uncover the exh port all the way. I disregard they spec dimension and use the pv timing marks on the inside of the cylinder as my baseline. I profile the edge and belly of the flapper to conform to the exh port opening as well as the under side of the exh roof. Marcus, if you remember Fas Wes mod of the CR 125 flapper, this is same idea, but the KTM is better b/c there are no passages through the center of the flapper only on the side where it bolts into the jug. So you won't have much to deal w/ in regards to an actuator rod running through it, get it? This along w/ working the subs slightly higher will get the bike to rev more, give the exh more BD, but you won't really have to work the head to keep CR w/i acceptable #'s.
Also, I do a gasket match mod to the base of the jug to keep the flow going under the piston. It includes knife edge the dividers and mating the jug to the cases. The 125 cases are made from the 200 cases. The 200 jug bolts up nice, the 125 jug hangs over into the cases, on one side by as much as 8mm. We all know this is no good.
You can do the usual "no hook" rear trans thing with great results, as well as working the boost port to shoot right up at the center of the head.
If you want to leave the porting alone, you can go after the head to work it. For good low mid burst, leave the stock base gasket in and cut the cyl head surface .39mm
For good top end - overrev w/ stock base gasket in
cut the head surface .29mm and remove about .35cc from combustion chamber bowl. Note to self, be careful cutting this head, it is a triple stepdown,,,,meaning there are multiple gaskets surfaces to deal w/.
This along w/ updated jetting, makes the 125sx a 250F eater. You can try 1468-69 G, 2nd position, 192 main and a 48-50 pilot for startes. I have done lots of 125sx motors lately w/ great results, if you guys are into the KTM's, make sure you go to www.ktmtalk.com. It is the largest KTM customer based web site in the world! Lots of great info on there! You can look under Jbonemotorworks or jman271 for a search to see some happy motors!!!! Also, there is a pic gallery showing some step by step mods for the gasket stuff!!! Post back-

 

[pete 2]

jman,
cant register at ktmtalk, wont accept my hotmail email.

 

[marcusgunby]

great info i will pass it on thanks.

 

[elf]

Jman, maybe you can explain something to me about the pv. The last time I had it apart I was looking at the flapper. With the acuator arm disconnected the pv flapper only moves up to a certain point then hits the roof, or top of the inside of the exaust port. but it doesent come close to opening as far as the exaust opening in the cyinder. So why is the exaust port cut so high up ?If I understand your post you grind off the top and bottom of the flapper so exaust port is higher when the pv is all the way up? Btw I got that stroker crank in my bike now. Hows that 200 working out for ya?

 

[Jman271]

This is for the 125, if you are talking about 144, once the bore is peeled back for the over bore, the exh port height gets peeled back also, so when the pv is in up all the way the pv flapper now become the new exh port height which should be about 27.5mm from top of the barrel w/ the 144. Did I say that right??? Anyway, my 200 is a monster, just put in a 38mm air stryker carb, it pulls crazy off the bottom, and revs to the moon! Let me know if I answered you question, I hope!!!

 

[elf]

Yes that answers my question. Its too bad they stopped making the 200sx, I was thinking of buying a 05. Oh well.

Pete2..If you become a subsriber at drn( Which is a good idea) you can get a e-mail account at drn. and then you can use it to join ktm talk. I had the same problem with hotmail at ktm talk but they accepted my drn e-mail...Just a thought.

 

[pete 2]

Elf,thanks for info on the email.

Jman the information you supplied is great,Just two more points,the cylinder overhang in the cases (125)do you advise cutting the cylinder or using epoxy in the cases to fix this mismatch i understand there is a top end/bottom end issue here,but which is more suited to the ktm.

the "no hook" part of your post,are you talking about using epoxy here as well?

again,thanks for your replies,there much appreciated.

 

[Jman271]

Yes on both areas. If you want a low end monster out of that 125, add epoxy to the cases and match them to the cylinder. This will give you more primary CR,(under piston) and boost low end and torque. Doing this and the rear hook will give you a great low end supercross type power. Machining the jug to the cases will yeild mid-top. My suggestion is that for overall increase, machine the jug, add the epoxy to the rear trans, fix the PV flapper, work the subs, get some of the jets I had spec'd and go rip it up!!!
ps- be careful of doing the epoxy yourself, you will need a right angle tool to get to it inside the port to massage it. Good luck-