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1 - 20 of 75 Comments Last updated Jun 21, 2013
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dustin

United States

#1 Oct 9, 2006
i would like some recamendation on wich is better 205 ofur stroke or 125 two stroke
Nicole

Spring, TX

#2 Oct 25, 2006
Does anyone know how or where I can get a KTM 125 2 stroke GP road racing bike?
BC Boy

Maple Ridge, Canada

#3 Nov 2, 2006
Looking for flaws on the 2003 KTM250EXC?
chris

Big Rapids, MI

#4 Feb 11, 2007
does anyone know what fuel mixture to use for the ktm sx 125?
bobby

Los Angeles, CA

#5 Feb 28, 2007
who knows the oil gas mixture ratio for a ktm 125 sx
sandyp

UK

#6 Mar 30, 2007
chris wrote:
does anyone know what fuel mixture to use for the ktm sx 125?
Hi there mate I have a 2002 sx 125 and have run mine at 40-1 with a good fully synthetic race oil I only use it on practice tracks but has been fine for the last year my mate does the same on his 2003 200 exc
burt

Canvey, UK

#8 Jun 16, 2007
Too much oil M8. 32:1 would be much better. Always ran my 2strokes @ that when i raced in the 90's. Raced 125 & 250's @ expert level & never had a engine faliure. Always used Castrol TTS fully synthetic oil.
bike boy

Subiaco, Australia

#9 Jun 16, 2007
chris wrote:
does anyone know what fuel mixture to use for the ktm sx 125?
Umm just bought one and im positive its 40:1
meeeegan

Australia

#10 Jun 18, 2007
i wana buy a 125
anyone know where i can get a good
one cheap?
RGeth

UK

#11 Jul 18, 2007
I have a KTM sx125 04 and theres thick gray oil coming from my piston breather!!! I looked at my gearbox oil and its the same colour and thickness. Can anyone tell me how gearbox oil got to my piston? It starts first time despite the oil that came out!! There was lots of it too!
Jon Wright

Europe

#12 Aug 2, 2007
burt wrote:
Too much oil M8. 32:1 would be much better. Always ran my 2strokes @ that when i raced in the 90's. Raced 125 & 250's @ expert level & never had a engine faliure. Always used Castrol TTS fully synthetic oil.
Be careful when you give advice - 32:1 is MORE oil than 40:1 not less. The first number is how much petrol and the second how much oil - so in 5 litres 32:1 is 5000/32= 156 ml of oil.
40:1 is 5000/40=125 ml of oil.
I have seen tighter numbers quoted (50:1), but I have had good results with 40:1 and Putoline MX7 on pump gas on my sons sx 85 .More oil in modern bikes just smokes . burns plugs and clogs powervalves / exhaust packing.
Jon Wright

Europe

#13 Aug 2, 2007
RGeth wrote:
I have a KTM sx125 04 and theres thick gray oil coming from my piston breather!!! I looked at my gearbox oil and its the same colour and thickness. Can anyone tell me how gearbox oil got to my piston? It starts first time despite the oil that came out!! There was lots of it too!
Easy one -
1 I'll bet you havent changed your gearbox oil for a while so its got saturated with aluminium and fibre particles from the clutch - also the water pump seal might have worn and some of the grey comes from the mix of antifreeze and oil. Easy to test - change the oil - if it goes back sludgy in one ride its the seal, if not, its just the bits from the clutch.
2. Not sure what you mean by piston breather, but anyway - the crank seal on the drive side (other side from the ignition)has worn and on the "suck" cycle of the 2 stroke process, it is sucking the gearbox oil into the crankcase where it sits in the bottom, being stirred by the crank as it spins. It will run for a while but be careful. If it runs out of oil - no gearbox, if it pushes the oil up into the cylinder, it might go bang with hydraulic pressure - no engine...its possible to replace the seal just taking the cover off, so you dont have to split the cases - unbolt & pull the primary gear off, 2 self tappers into seal pull it out, tap in a new one square, everything else back in and jobs a good-un.JUST BE SURE TO CHECK THE MAIN BEARINGS BEFORE YOU PUT THE SEAL IN - otherwise it will only last a ride - if they are worn - its a full engine strip - Not too difficult to do yourself if you get the manual.
Cheers,
Jon
RGeth

UK

#14 Aug 14, 2007
Thanks Jon!! Ive changed the oil on my ktm and will take it for a ride soon. I was a bit worried untill you responded!
The oil came out of the gearbox breather on the left of the engine (my mistake!) thanks again for the advice ill post annother comment after ive ran the bike.
glen core

Christchurch, New Zealand

#15 Aug 28, 2007
has anyone put a jd jetting kit in a 2007 ktm 125sx
or got a good setup
Jon Wright

Europe

#16 Aug 29, 2007
RGeth wrote:
Thanks Jon!! Ive changed the oil on my ktm and will take it for a ride soon. I was a bit worried untill you responded!
The oil came out of the gearbox breather on the left of the engine (my mistake!) thanks again for the advice ill post annother comment after ive ran the bike.
No problem mate - hope it helped. As its not oil getting into the combustion side, even if it is the water pump seal its a cheap / easy fix.- if it is that, my advice is - fix it yourself with a genuine seal, but dont use plain water or cheapo antifreeze as the aluminium and magnesium parts dont like it - use lots of good bike specific antifreeze and you'll never have to buy a new casing -
One more thing... to everyone - enjoy your MX - lifes too short not to !
Cheers,
Jon Wright
orangutan

Fitzroy North, Australia

#17 Sep 4, 2007
jon next time your online please could you adress my post you seem to be the cluie one thanks im in oz im a pom too please help cheers orangutan.
pacificktm

Makawao, HI

#18 Sep 8, 2007
Just rebuilt the top end of my ktm 250 exc and my compression problem was fixed but not my oil burning one. Started the bike up and ran it easy and it started burning oil then it took off with a crazy air leak. I suspect because it was doing its own gas air mix. When you have a auto clutch this is very scary. Could this be a combination of both crank seals? Anyones help would be appreciated.
pacificktm

Makawao, HI

#19 Sep 8, 2007
Just to get things strait the oil that was burning was definitaly trans oil. My whole exhaust was coated.
John347c

Florence, KY

#20 Sep 9, 2007
My son just bought a 2004 125sx it is hard to start with a kickstarter, but fires up with a jumpstart. Also found that the cdi box is cracked and after washing the bike it seemed to develop a miss. could this cdi be causing hard startiing or a miss in the engine
Jon Wright

Europe

#21 Sep 11, 2007
orangutan wrote:
jon next time your online please could you adress my post you seem to be the cluie one thanks im in oz im a pom too please help cheers orangutan.
Gday mite !
Thanks for your request - hope I can help.
Ok- I cant see the bike myself (Oz?- I wish!)so i'll try and describe the problem first, but if its a different prob, just mail back and correct me -
Ok -
- There is 100% no drive at the wheel, i.e. you run the engine put it in any gear (not just 1st gear) and let the clutch out and you can stop the back wheel with the brake without stalling the engine.
(dont do it too much- you'll make the damage worse!)
I assume you were riding it one day and it just went?(could be a different reason if it was rebuilt then it didn't work)
OK - look at the countershaft sprocket first just in case (I'm sure you already did this)- Is it worn round and smooth? Take it off - are the splines on the sprocket and output shaft in good order?
So - delve deeper - There are quite a few posibilities (list at end), but my first instinct is the primary drive gear on the RHS of the crankshaft. Its held on with a woodruff key (a little half moon bit of metal). If the nut holding it on loosens a bit, it can move around enough to shear the key (especially on a 125 where you feather the clutch a lot to drive out of turns). The engine would run perfectly but transmit no drive to the gearbox.
So - take the full LHS casing off (OK engine in frame)and take off the nut that holds the gear onto the crankshaft.
Its tight so I normally use a wedge of pine between the primary gear (on the crank) and the clutch ring gear, but that wont work if its sheared so if its still tight you might have to take the barrel and piston off, make a nice flat block of wood that fits over the crankcase mouth (leave a gasket on it to avoid damage), and put other blocks either side of the con rod running front to rear that the gudgeon pin can bear on when you turn the nut - sounds complicated but is really easy.
Take the nut and gear off - if its the woodruff key it will be obvious - chopped and smeared. Clean the keyway up - if its not damaged (widened and uneven) count your lucky stars, chuck in a new key, tension the nut up correctly and you're back in business. If its burred, you can put a new crank in or have it built back up with weld but do not be tempted to weld the key in, or the gear to the shaft - it wont last two minutes and then you wont be able to get the crank out of the casing !
Anyway - I spent a lot of words on that - if its not that, check the rivets that hold the clutch gear to the back of the clutch basket, and also that there are enough clutch plates in. Also check that its really going into gear - if one of the pins that hold the selector forks snaps, it will click up and down but not really go into gear.
Good luck - let me know what it was when you find it.
Cheers,
Jon Wright

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