JETTING-Can anyone answer this?

I have a Euro spec 450EXC, with no mods. (But with the restrictors all removed, a OBDTN needle fitted, and the standard quiet silencer).

I have a problem of bad hesitation off idle when the throttle is just blipped, but only when at altitude (Max 3000ft) or when hot, in slow going. I live at sea level and the temp is around 20degrees C at sea level at the moment. The bike runs fairly well there, or when warming up.

It doesn't need the choke for long, and I have tried various positions of the needle circlip, from position 2 from the top, to 4 from the top, with no difference. I did notice a lack of midrange power when in the leaner position (position2).

I have also tried various idle screw settings, from a half turn out, to 2 turns out also with no noticeable difference. However, I have found that that the engine will run with the Idle screw fully in, leading me to believe the pilot circuit may be too rich (Even though this is only a 42 and I notice that some of you lot run a lot larger pilot than that with no probs). I have not touched the squirt circuit, but I am led to believe this is adjustable on the 03's.

Anyone got any ideas? It is the only thing left spoiling the ride, after sorting a myriad of other glitches on this 4 month old machine,(Possibly made last..on a Friday afternoon!!??) with currently: 2500kms up, and just starting to loosen up now.

Full jetting specs as follows;

Main 178

Needle OBDTN

Pilot 42

Idle screw normally 1 1/4 out

Air jet 200

Idle jet 100

Cheers :)

I wish i could give you more but here is what I've got; It definetly sounds as if the engine is running rich at or near idle. I'm suprised to here that the fuel screw makes little or no difference as that thing changes my set-up dramatically. 42 is leaner than the 02 bikes but the fuel screw should still make a difference. Could it possibly be that the float adjustment is high enough to cause your symptoms? I set my bike up to the point that it is lean at idle to 1/8 throttle when cool, that way once hot (during a race) it responds properly. Mine is picky about the fuel screw adjustment i wont give #'s as I have a 02 520 and they would differnt anyway but I sometimes richen it a 1/4 turn when I trailride and know the bike wont be getting to warm for any amount of time. When mine is set on "kill" it will idle well cold but wants the choke longer and will hesitate until the motor gets hot then it runs great. when set rich it will run great cool and use little choke but will become sluggish in the tight stuff and if ridden in a long enough tight section will begin to hesitate. You may also want to take a look at your accelerator pump timing and duration. You should have little trouble finding posts on this subject. Still though the accel. pump wouldn't justify the lack of fuel screw response you described. Good luck and don't give up on her you will be rewarded in the end. (hopefully not the rear end!) :)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Ponch
      I have a 2007 450 EXC that I recently installed a new clutch slave cylinder on. Per the 2007 KTM service manual it clearly states that the clutch needs to be filled with hydraulic oil, which I did (magura blood). That was yesterday. I went out to double check the level today and when I removed the cover, the rubber seal was all contorted and out of shape. I then looked at the cover and it's a Brembo clutch and says "DOT 4 brake fluid only".
      I flushed the line and the master cylinder about 7 times with DOT 4 brake fluid and there was no sign of the magura blood left in the system. My question is: other than the rubber boot on the master cylinder, what damage might have been done by putting in the hydraulic oil? It was in for about 24 hours.
      Thanks in advance for any advice!
    • By pumpernickelBrad
      Hi Folks!

      Sorry if there are a bunch of threads already but I used the site's search function and didn't find anything so far...

      I just found a decent deal on a '14 350 EXC-F with 11k km (unknown hours). Has a few goodies including skid plate, hand guards and it's for sale for about $2k CAD less than a '16 with 6k km on it.
      The bike is in showroom condition (appearance) with no indication it has been offroad at all.

      What would be the gotchas that would make this deal realistic? I'm coming from a WR250R where the engine lasts forever, is 11k street kms high for these bikes? 
      Are there any big defects in the '14s that I haven't dug up yet?
      With no service records what things should be done, checked, etc?
    • By Brannnt
      I purchased an '06 525 EXC some time ago, and recently pulled the motor out of the frame to address some other issues. When I removed the clutch slave cylinder, I noticed an issue the previous owner neglected to tell me about during the purchase.
      It appears that at some point, the chain broke and damaged the engine case near the clutch slave cylinder (see pics, please). I have noticed that the clutch does not fully disengage (bike lurches a bit going into gear, neutral is hard to find... its worse when engine is cold) ... I did not notice any leaks around this area (mineral oil or engine oil) before or during disassembly. 
      The previous owner (or someone) repaired it with some sort of epoxy.
      Without doing my due diligence (checking clutch fluid level, bleeding) I hesitate to state that this is the cause of my clutch disengagement issue ... but pardon my ignorance here and help me out: How bad is this?  Am I looking at replacing my engine case here or is the previous owner's jerry rig good enough?

    • By Black Sox
      Just bought a new 2017 350 excf ,will be doing 98% off road ,ordered skid plate bark busters ,
      my ? Is what's the best easiest way to eliminate rear fender light assembly.I still would like to have a break light.
      xcf fender will fit so dealer says,under $50.00 👍But xcf brake light $125.00 .👎What's the best economical way of doing this?
    • By JNV
      Hi friends from Spain.
      Mi new KTM