Dirty bike jetting

Discussion in 'Tech' started by DWhyte91, Sep 15, 2014.

  1. DWhyte91

    DWhyte91 Well-Known Member

    A friend of mine has bought a 2014 ktm 250sx. He's just getting back into riding dirt and I've been taking him trail riding with me. I don't think he's riding the bike very hard or clearing it out in the tight single track which is understandable. He fouled 3 plugs yesterday. I took the bike for a spin and it sounds like the pilot jet is too lean when cruising, the bike pulls like a mother up top and rides normal aside from the knock at partial throttle. I pulled the plug after taking it for a spin on a fire road and it was nicely browned. With him fouling plugs in the tighter trails what should be adjusted? I'm going to go up one pilot jet to remove the knocking at low throttle inputs but aside from pulling his skirt out of the chain or carrying a case of plugs what should I look at?
  2. rob linders

    rob linders Well-Known Member

    I don't know my KTM model numbers, but that sounds like a 2 stroke number. If so, how much oil is he mixing in per gallon? If he is an older rider, he could be mixing in a bunch more oil like we did when I was a kid. With the new synthetic stuff, I believe it calls for about 50-1or even 60-1.
  3. Banditracer

    Banditracer Dogs - because people suck

    What you're saying is contradictory. If it's fouling plugs it's rich so going up on the pilot size will make it worse. I assume there's a adj. fuel screw on the carb, I'd play with that a little. With the bike warm and idling turn the mixture screw in / out until you've got the idle at it's highest point then adj. the idle speed if you have to. That should get you pretty close as far as idle to 1/4 throttle.
  4. Joe Morris

    Joe Morris Off The Reservation

    :stupid: When I had trouble fouling plugs on my bike this was the reason. The manufacturer recommendation levels are just absurd IMO. I switched to Benol (for the smell) and followed their recommendations which solved the problem.
  5. DWhyte91

    DWhyte91 Well-Known Member

    Sorry I thought I put in the mixture, 50:1. I know it's contradictory which is why I'm confused. There's definitely a knock while cruising at partial throttle. It's a two stroke btw.
  6. Joe Morris

    Joe Morris Off The Reservation

    Eh, I got nothin' then.
  7. t500racer

    t500racer Looking for the Bad Teacher's thread...

    I wouldn't make any adjustments until you confirm that the float level is properly set and that the needle/seat is sealing properly. Ethanol fuel wreaks havoc on rubber tipped fuel needles.

    As far as the "knock" I think we need more description than that. Is it four-stroking? Piston slap?
  8. NOLAracer

    NOLAracer Well-Known Member

  9. DWhyte91

    DWhyte91 Well-Known Member

    It's a brand new bike with two rides on it. The knock happens when your maintaining speed. The float is fine as the bike can be ridden wot as much as you like without any hesitation and doesn't pour fuel out of the overflow when parked. I leaned my pilot jet out on my RM250 and got the same knock untill I switched the jet back which is why I'm going to richen his up. The knock is definatly not suppose to be there and if it's piston slap ktm has some esplanin to do. I almost want to make the bike not idle so he has to blip the throttle constantly and not rely on the idle, maybe that would help keep it cleared out. I was thinking of dropping the needle one position swapping the pilot jet.
  10. DWhyte91

    DWhyte91 Well-Known Member

    I'll try his testing on the pilot circut and adjust the airscrew. I'm thinking the pilot is too lean and the needle setting is too rich but the main is correct. After riding with the bike at wot for a good stretch through all the gears the plug looked good.

    Ps airfilter is also clean.
  11. Pepper381

    Pepper381 New Member

    Hi...DWhite991. I also have a 2014 KTM 250sx having the exact same issue? Please let me know what you finally figured out to solve the problem!! Thanks Pepper!
  12. Linker48X

    Linker48X Well-Known Member

    What it lacks is heat. Put a hotter plug in it. He isn't laying on the gas and it won't burn clean. SX means Supercross, riding wide open, not putt putting in the woods. Even an experienced rider can have this problem on tight trails. You can go from 9 to 8 no problem, and maybe with attention a 7 if the 8 doesn't fix it, but if he does that, no wide open 2 track, keep the revs and the load down. You might also increase the pilot too. Oh, and don't overoil the air filter. Have your buddy buy some of those little plug carriers and a fanny pack too.
  13. racepro171

    racepro171 to finish first, first you must finish!

    one thing i noticed when i was on 2 smokes is if your a put put rider, you need a quality oil. if your on it all the time on long trails, you could pretty much run engine oil ( not really, but you get the point)
  14. Jdub628

    Jdub628 Member

    Hotter plug if it's a 9 try an 8 as stated above.
  15. Pepper381

    Pepper381 New Member

    Thanks! I will mess with the pilot and try a hotter plug? I race the USRA Hare scrambles and the bike is on the pipe for 75-100miles. It does it at an idle/warming up and even after its totally warmed up. I don't notice it when I race because its past the slap noise. I said screw it the last 4 races and it hasn't brunt down yet! I hate having it run like this!! Thanks again!!
  16. Pepper381

    Pepper381 New Member

    I run Gearsaver 80w in the transmission..Maxima SuperM 40:1 and a TwinAir filter.. I tried AV gas and nothing.. I tried Klotz octane booster and nothing, thinking it might be low a low octane issue? I read somewhere to go 2 steps leaner than the manual jet chart when you run a spark arrestor and I plan on trying that. It has never fouled a plug!
  17. Jdub628

    Jdub628 Member

    Are you running race gas?If so 50/50 or straight. Those bikes have alot of compression and tend to ping at a slight load.
  18. Jdub628

    Jdub628 Member

    You could try raising the needle clip as well. I believe raising it leans it out.
  19. DWhyte91

    DWhyte91 Well-Known Member

    Lol don't think the bikes even been ridden sincce shortly after I made this thread. We did get the jetting set so he stopped fouling plugs just but moving the clip up one postion but I think the knock was still there. As Jdub stated I'm pretty sure it was pinging.
  20. DonTZ125

    DonTZ125 Purveyor of Neat Toys

    Correct. Clip up = needle down = less fuel at part throttle.

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