Does anyone have the slightest idea on what the operating temp is for a 99 yz 400f? the last two times that i have ridin it it has either boiled over or its reached 250 degrees and does not idle. So far i adjusted my pilot screw and have that dailed in and and also did the jet clip but on the clip i had to move it to the sixth slot down from the top and theres only seven slot. I have it to idle but the idle screw is still all the way in. You think i just need to jet a jet kit or wat? And would rejetting it make it run cooler?

No, it's very unlikely that jetting will make it run cooler unless it's so far off that it runs badly because of it.

If you do a lot of low speed riding in and around tight trails or spend more than a minute at idle, that's your culprit there.

The 400 had smallish radiators, and that makes matters worse than with the rest of the YZF line. Radiators from a WR, or from a YZ426 will help, but you should also make sure your radiators are clean and the airflow unobstructed by debris.

Temps will range from 140 or less at an easy 30-40 mph cruise upward to a boil on a tight trail.

water wetter helped my 99 400f...pure in the whole 12 oz. bottle...mine never boiled over and woods riding was pretty much all i did with that bike.

oh..i also made that bike a 426 with a kit from thumper racing...never changed the radiators and it never boiled over

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