Fuel Mix For 02 Ktm Sx-125

[Pjc87]

I recently got a killer deal on a 2002 ktm sx-125, it needed a new stator, so I put a new stator in it and it fires up on the first kick now. The bike came with a pro circuit platinum series pipe and a pro circuit silencer a short one. I have ran about 3 gallons of fuel through it since getting it and I have been using amsoil interceptor oil with 91 octane ethanol free fuel mixed at 32.1.
I have noticed the bike smokes quite a bit with it mixed at 32.1 even when going down a straight road wrapped out in 6th gear.
I've been trying to find out what mixture ktm says to use in the 02 125 but I can't find it, I have read other people say ktm says to run 40.1. So I'm going to run 40.1 in my next tank of fuel and I'm going to see if that limits some of the smoke, I was thinking maybe the 32.1 is too lean for the bike and that's why it's smoking, it's not smoking extremely bad it anything like that, but it is smoking if that makes sense and it still smokes when you have it wrapped out all the way, and I don't know how accurate this is but I've been told if it is smoking with it being wrapped out its most likely running to lean.

 

[Rich Rohrich]

32:1 is the correct mix for the bike, putting less oil in the fuel will only wear things out quicker and won't make it smoke less.

Start with the basics:

1. Clean the insides of the pipe of any old carbon and oil.
   
2. Repack the silencer.
3. Fresh plug in the correct heat range. Lots of people stick too cold a plug in 125s and cause the issues you are describing.
4. Clean the ignition coil connections and make sure the system has good clean ground wires.
5. Check the compression and make sure the rings and piston aren't just worn out

Once the bike is mechanically sound, then check the Two-Stroke forum here for tips on getting your jetting dialed in.

With the correct oil and a sound engine properly jetted you can run the bike at 16:1 and still not have it smoke when it's run hard.

Good luck and let us know how it goes.

 

[Pjc87]

Coil is good and so are the connections, plug is brand new, it's a ngk I believe it's a 9 series?? Not sure what kind of shape the engine is in got the bike used. I could do a compression test on it and see what it reads, what kind of psi am I hoping to seen if the engine is in good condition?
I seen some people saying ktm says to run 60.1 in some of there newer bikes.
And I seen other people saying ktm suggests 40.1 in thier 125s from 99 to 03 but I can't find that. I can't find ktm's manual for the 02 sx-125.
Are you sure 32.1 isn't too much oil making the engine run lean? I'd rather veer on the safe side of things so if running 32.1 is being safer then 40.1 then ill do it. Bike runs good, has a pretty intense power band, I noticed this bike doesn't like to putt along it wants to be going and going hard. I have taken it to my local motocross track and it does great, only complaint I have with it is the suspension is a little rough, my friends cr rides a lot smoother but the power on this ktm is great, I think the carburetor could be cleaned because I have noticed the idle is un steady, sometimes it idles a little lower then other times.

 

[Okiewan]

If Rich wrote it, he is sure.

 

[arnego2]

Whatever companies recommend the way to actually see if your 2 stroke premix ratio is right for you is about the premix fallout pooling in your crankcase. Above 2mm and you use too much oil for your riding style. The premix oil is mainly used to lub your bottom end like crank shaft bearings and con rod bearing, very little reaches you combustion chamber.

As mentioned if you get a lot of smoke you might have to look elsewhere, crank seal clutch side or head gasket i.e. Do you loose coolant or gear oil? How does the smoke smell?

An unsteady idle suggests an airleak, be extra careful here those could cost you your engine.

 

[Rich Rohrich]

Arnego2 brings up an excellent point that I failed to mention as part of the mechanical soundness checks. The crank seal on the gearbox side is a prime candidate for this type of issue especially on a used bike. Change the gearbox oil, measure in an exact amount and then re-measure it next time you change it. It could give you an indication whether or not the gearbox oil is being burned.

If you are unsure on who to trust for an oil recommendation I'd suggest following the guidelines of the manufacturer of the oil. They know what the additive package is in the oil, so they have the best idea of how it should be mixed for the conditions and engine type.

 

[Pjc87]

I'm taking your word on 32.1, I have changed the transmission oil twice now and it was leaking at the drain bolt a little bit, bit I out some Teflon tape around the boot and it doesn't leak there anymore. The smoke is blue and it just smells like 2 stroke exhaust to me. I don't think there is an internal leak with the the tranny fluid and engine because I am running type f transmission fluid and was told it would burn white if it was leaking into the engine.
I haven't lost any coolant in the 5 hours or so that I've put on the bike, I check it every time before I start it up. Where would the air leak be coming from? The piece between the engine and carburetor looks good, it does have a couple small stress cracks in it but nothing huge, could I use carburetor cleaner and spray around that piece to see if the idle changes again?

 

[arnego2]

Airleaks can come from various sources, rotor or magneto side crank seal, even the clutch side crank seal could let air though if leaking on the upper side of it, , it just needs to be above the oil level. reed cage, even carburetor itself could it be.

I had to repair a bike once where "specialists" dismantled the carb completely, breaking some of the seals. A nightmare really.

 

[Pjc87]

I have a feeling if there is an air leak it's at that rubber looking piece between the engine and carburetor, which is called the reed cage correct?
I took an even closer look at that piece today and it has a few stress cracks in it.
What do I need to buy to fix this issue? Is it called a reed cage or should I buy a v-force reed set up for it?

 

[arnego2]

No idea mate, could well be. I like the boyesen reeds on the stock reed cage of the YZ250 which I love :) and even too on my RM260 with a YZ yamaha engine.

 

[Pjc87]

I don't know for sure if that's where the leak is if it even has one I was thinking maybe the carburetor needed cleaned. So how do I track this leak down? Is it the same as checking for a vacuum leak on a v-8 engine? Start it up and spray carb cleaner around the suspected area and listen for a change in idle speed?

 

[arnego2]

That would do, cleaning your carb is also a good idea :)