KTM 125sx pilot jet question

[mike-evans]

Hi all. Ive just bought a KTM125sx 2006, not yet used it properly due to weather, Ive only give it a blast up and down the lane behind my house, plan on using it this weekend. Pulled very well and smooth when I did take it up and down the lane.

Bike has plenty of compression.

I noticed where the exhaust joins the cylinder that it was leaking a bit off spooge, so I fitted new orings yesterday, aswell as a clean oiled filter.

I started the bike to see if the orings had sealed. Warmed the bike up on the stand, and whilst grabbing a hand full of throttle, theres a hesitation and then it revs clear. Im thinking its a lean pilot/air screw circuit..?

As Ive not yet taken it out in the track, Im not 100% sure how it will run. Maybe fine once its warmed up and had a good clear out....

Another thing is, I dont know how long the petrol and 2t oil has been in the fuel tank for, as it came with a full tank...

What would be the best thing to do when I take it out.
Fill the tank with new petrol and 2t oil?
What should I do about the low end bog?

Dont want to seize the bike up...

 

[BSWIFT]

Read thru Spanky's Jetting guide at the top of the 2 Stroke Forum. Follow the guide and get it jetted correctly. Worth the time and you'll understand your bike much better afterwards. Make 1 change at a time and test. Do the changes in the order the guide tells you and you will be good.

 

[FruDaddy]

Give me the altitude and approximate temperature where you will be riding and I can give you the baseline jetting information from KTM.

 

[mike-evans]

Sorry guys, theres more questions from me....

I've just bought a Doma system for the bike, and have some jetting questions regarding that...

Approx altitude 300ft, temp around 3 degrees.

I understand the principle behind it all and one adjustment at a time etc.....

But the main question I have is:
Would it be best to fit the new pipe, then ride it and see how it feels aswell as taking plug readings?
Or, richen the main 1 then ride it?

I'm afraid of running it lean straight off.....

 

[FruDaddy]

Assuming Fahrenheit this should get you started.
(-2-20 degrees F, 0-1000 ft)
Air Screw: .75 turns out
Idle Jet: 52
Needle: R1468D
Clip Position: 4 (from top)
Main Jet: 168

IMO, err on the side of rich and get it running right before you complicate things with mods. This way the changes will be easier to predict.

 

[mike-evans]

Stripped the carb apart today to confirm my jetting.

Main 188
Pliot 45
Needle R1469D 2 clip position from top

so jetting is as the manual.

After putting the carb back on the bike, I run the bike (on stand), got engine warm and while grabbing a handful of throttle, theres a bbaaaaawwwooooooonnnnnggggggg before it revs clear.
If i open the throttle slightly then rev it, its fine.....

Think I may go 1 richer on the pilot?
Would dropping the needle 1 clip help richen it to take the bog out?

 

[_JOE_]

Don't pay any attention to the way it runs on the stand. Take it out and run it for 5 minutes or so under load and you'll be able to start tuning. Follow the jetting guide exactly and thoroughly. If you're worried about it being too lean from the get go, drop the needle clip a notch or two and turn in the air screw a half turn. If it's dripping spooge I doubt it's dangerously lean.

Also, it is possible to over oil air filters. Not common, but possible. If you wrap the filter in paper towels and squeeze it out well you'll know you have just the right amount of oil on it.

 

[mike-evans]

Don't pay any attention to the way it runs on the stand. Take it out and run it for 5 minutes or so under load and you'll be able to start tuning. Follow the jetting guide exactly and thoroughly. If you're worried about it being too lean from the get go, drop the needle clip a notch or two and turn in the air screw a half turn. If it's dripping spooge I doubt it's dangerously lean.

Also, it is possible to over oil air filters. Not common, but possible. If you wrap the filter in paper towels and squeeze it out well you'll know you have just the right amount of oil on it.

Yeah I will take it out on the weekend and run it....

Just a question I have though.. With the bike running on a stand, I can understand that the engine may load up and go rich until its cleared out... But how would running it on a stand make it lean?

Just something I was thinking about...

 

[_JOE_]

Running it on the stand won't make it lean.

 

[sbest]

All good advice here guys, but here is my take on the situation as an old guy who has been running 2 strokes since 1974:
1) It is an 8 year old used bike new to you. Leak test the engine to make sure the case, gaskets and crank seals are not leaking. You do this by plugging the intake with a bung at the carb mount and with an expanding rubber plug in the exhaust hole. You pump the engine up with 7psi and see if it holds it. If the engine is leaking air you will never get jetting right.
2) Drain the tank and put new gas/oil mix in. Buy an excellent brand of 2 stroke oil and stick with it. Mix it as to the instructions which are 50:1 for your bike. Sticking to known good components and manufacturer's procedures makes things MUCH MUCH easier to troubleshoot.
3) Follow the KTM manual for jetting for your altitude and temperature. These recommendations are on the rich side but will work and are safe and will get you running safely IF there are no case leaks. You checked this in #1) right?
4) Run it, warm it up gently, look for problems and leaks, solve them. Stick a new plug in it and run it up through the gears. Shut it off and pull the clutch at top speed, then pull the plug and look at it. This is called a plug chop. Learn to read the plug. This will tell you if the main jet is right. You may be able to lean it out a size or two for better performance.
5) Jetting pilot (idle) and needle are bit complicated to explain here but well worth doing for crisp response and engine life. Read up on it and learn it.
6) NOW stick your Doma pipe on. Jet rich a jet or two if you want and plug chop it again. You will be able to read if you are lean or rich on the main.

Make all mods one at a time and only to a known well working engine. Sticking to as close to manufacturer's specs assures the longest engine life and easiest trouble shooting. Stock these engines work well and long, learn to keep them running stock before you start experimenting, and then just change one thing at a time.

Here is a leak tester and a plug reading chart: