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KTM 250 EXC mid throttle sputter

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My buddy bought a 99 KTM 250 EXC with a 98 RMX 250 carb and now it sputters at steady mid throttle.  2 strokes usually sputter a little at a constant throttle, I mean they are a race bike not a cruiser, but this sputters like no other 2 stroke I've rode.

 

So I am pretty comfortable working on carbs and diagnosing them except for this one.  The problem is that the 99 KTM EXC starts up no problem, idles great, runs great WOT through all gears, but when mid steady throttle it wants to sputter and foul a plug.

 

1. Disassembled and cleaned carb, tank, pep cock, and remix fuel and instal new plug.

2. I thought that the needle needs to be replaced since that controls mid throttle. 

3. He swapped the carb tonight and put back the orignal KTM carb and it rode better but still the same issue jsut not as bad.

4. How would the CDI or other ignition issue be happening to make the same problem and how do I check it?

 

This is what the RMX carb on the KTM currently has:

I think it is PJ Carb

Needle - R1472M 1L

3rd Position

Main - AB175

Pilot - 55

AF screw at 1.5 turns out

 

Not sure what type the KTM carb is jut I am told it is the same PJ style but here is what is suggested:

45 pilot @ 1.5 turns out on the air screw 

170-172 main jet 

NOZH needle in the 2nd leanest clip (2nd from the top)

 

Thanks in advance

Edited by arcboy

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Anyone have any ideas?

 

Just dropped it off to a technician and hope he can get it ready for next weekend.

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change the needle position all the way in one direction to see what you need, leaner or richer....most likely dropping the needle two slots will do it, if it's the right needle.

 

Have you adjusted the air screw? You have to do that first.

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change the needle position all the way in one direction to see what you need, leaner or richer....most likely dropping the needle two slots will do it, if it's the right needle.

 

Have you adjusted the air screw? You have to do that first.

Yes adjusted both and the air screw doesn't take it away and adjusting the needle either makes the spark plug look leaner or richer.

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