Is this a jetting issue ?

Hi there.

I have an 04 YZ450F and am pretty close to sea level, maybe 300ft above. I am coming close to setting it on fire. Here are the issues.

I ride mostly trails, sometimes pretty tight, sometimes less.

When ever cranking the throttle from 1/4 to anywhere past that, the bike always sputters for about 2 seconds, then takes off like a bat out of hell. That 2 seconds is sometimes all I have to accelerate before I need to slow down so it is slowing me down a lot.

I was convinced it was too rich so I started to lean it out.

I dropped the needle to the 3rd clip - that appeared to help a little, but it was still there.

I then changed the pilot to a 42, it used to be a 45. No difference.

I then changed the main to a 165, it used to be 168. No real difference.

I have moved the fuel screw around and if I lean it out just a tad I get a hanging idle but no difference in the bog.

It seems to be worse when the bike is very hot, say after a tight area, or after a lot of sand etc.

I did the o-ring mod, felt a little better but at times will still bog just as bad.

Once it makes it past the bog it pulls very strong, it is just a serious pain as it awalys first sputters, then flies out of the gates.

I don't feel too comfortable dropping the needle any more.

Any suggestions ?

Check the slide plate to see if it is assembled upside down (the flat side with the hole near the edge needs to be on the bottom), or cracked, and possibly missing a corner. Another thing to try if that fails is disconnecting the TPS. This will put the CDI in a base timing, "full throttle" mode, and will tell you if you have a problem with the ignition mapping. That could still be either the TPS or the CDI, however.

Thanks Gray, will give that a try.

I checked the slide, it is in right way up.

Will try the TPS sensor disconnected today.

I am leaning toward the AP putting too much fuel in when the throttle is blipped.

Can the AP be adjusted ? Is there a procedure for it ?


Can the AP be adjusted ? Is there a procedure for it ?


Yes, and yes. It's in the manual.

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