2007 KTM 250sx Jetting Question/Help

So my buddy went and picked up a 2007 250SX. Ran decent, wouldn't idle. He is new to bikes, so it ended up in my garage for a once over....

Long story short, the bike was running with a 1/3 of the piston skirt missing on the exhaust side. So that is all being taken care of. While I am waiting on parts I cleaned the carb and checked jetting. Since it will have a new top end, I want to make sure the jetting is good, or at least in the ball park.

The jetting seemed odd to me, but I am far from a jetting expert.

Located Central Texas (Austin) We ride Hidden Falls mostly, but will be Emma, CTOR and the others in the area. He is a noob, so on the slower side...


Jetting in Carb currently
Slide: 6.5
Needle: N3EJ
Main: 165
Pilot: 38

Stock 07 250SX Jetting
Slide: 6.5
Needle: N1EL
Main: 158
Pilot: 45

Seems odd the went richer on the main and leaner on the pilot. Should my pilot be closer to a 45 since we run slow trails? And maybe lower the main?

Jets I have on hand are

Mains: 152, 160, 162, 168, 170, 175, 180
Pilot: 48, 45
Needles: NOZE, NAFG, D514

Lets say the stock jetting is for 70 degrees at sea level so the hotter it is the smaller your jets. the colder it is the bigger the jets.

On my 14 300 my needle is on second groove ,pilot is a 38 and main is 162.

Your jetting seems close to mine......and I have a 250xc.

07_919 said:

Lets say the stock jetting is for 70 degrees at sea level so the hotter it is the smaller your jets. the colder it is the bigger the jets.

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Thanks!! I new temp came into play but wasn't sure which way

Remember just comparing jets will get you in trouble. The needle taper and diameter are just as important. The amount of fuel delivered is about the relationship of the needle and jet. Example a guy with a 168 main could be running richer than a guy with a 172 main depending on the needle.

bwdmax said:

Remember just comparing jets will get you in trouble. The needle taper and diameter are just as important. The amount of fuel delivered is about the relationship of the needle and jet. Example a guy with a 168 main could be running richer than a guy with a 172 main depending on the needle.

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Very good point. Sounds like people have good luck with a Suzuki Needle. So I am looking at getting one of those as well. Need to start reading up on needles more and how to be able to determine what changes I need.

The needle is very important. I went with the JD needles. Liked them better than the Suzuki needle.

ekms377 said:

The needle is very important. I went with the JD needles. Liked them better than the Suzuki needle.

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Any idea if the JD needle out of a 200 would work? Its a Keihin PWK 38 carb.

I put a JD Jet kit in my KX250 and a 200exc and they've worked great in both.

I think the smaller bikes had 38s and the bigger ones had 36s. Not sure on slide or needle.

Have you even ridden it yet? I would do that first. Also, turn out airscrew to 1.5-2 turns out.

ekms377 said:

I think the smaller bikes had 38s and the bigger ones had 36s. Not sure on slide or needle.

Have you even ridden it yet? I would do that first. Also, turn out airscrew to 1.5-2 turns out.

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Got it all back together yesterday and took it for an easy stroll around the neighborhood for initial break in. Brought it back and set the air screw and idle. I rode it very easy avoiding high RPM but it seemed to run great. I'll have to wait and see how it does when I can really get after it.

When the bike is just sitting and idling.....crack the throttle open real fast. Should be no bog or hesitation.

You should do at least 2 heat cycles on a fresh ring before riding it.

ekms377 said:

When the bike is just sitting and idling.....crack the throttle open real fast. Should be no bog or hesitation.

You should do at least 2 heat cycles on a fresh ring before riding it.

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Off idle it comes right to life with no hesitation or bog. and settles back down to idle nice as well.

As for the 2 heat cycles, I've read everything from start it and let it idle on a stand for several heat cycles to the other extreme of get on it and rip just like normal.

The 07 250sx manual says to run in the engine for the first 3 hours by keeping Maximum engine performance less than 70%...

What ever that means...

My understanding of "seating" the rings is from old motor technology, where you had to keep RPM's low for rings to seat. High RPM's would allow the rings to spin and never seat properly. But with the rings on our pistons having the pins to prevent them from spinning, "seating" the rings is not necessary like previously.

This is what I've always done:

http://www.mototuneusa.com/break_in_secrets.htm

Didn't know someone was writing websites about it, either.

Got rid of our 1.8 turbo Jetta (due to paint/looks issues) at 135K, not a whiff of smoke, ran like new.

Still running my 4Runner, 240K, still runs like new, no smoke anywhere, and still gets the same mileage as new.

Bike still doesn't have enough mileage to tell.

So it works for me. And my cars/trucks/bikes.