Jump to content
Sign in to follow this  

JETTING-Can anyone answer this?

Recommended Posts

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 :)

Share this post


Link to post
Share on other sites

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!) :)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:

Sign in to follow this  

×