~04 WR450 high speed jetting issue~

I'm having an issue with the bike running clean in the upper RPM's. It runs fantastic everywhere exept about 3/4 throttle, and then it has a total flat spot/bog-like the motor completely cuts out for an instant and then it gets past that and it's fine. It either does that or it will get to that 3/4 throttle(aprox) and it will sound like it hits the rev limiter-kind of that misfiring sound. We're only about 600 ft. elevation, and it has an FMF pipe with the stock header.

I did a search, and haven't looked at the jets I have in, but the guy I bought it from said he had it richened up a bit. The bike is almost brand new with around 20 hrs. at the most. He said he had the valves checked before he sold it to me, and it only needed slight adjustment which he had done. The bike starts super easy.

I disconnected the TPS and I didn't notice any difference at all.

Does this sound like I need to go richer-maybe richen the clip position? Or.... Anyone willing to help me out will be much appreciated. Thank you.

First, if the valves needed adjustment at 20 hours, there may be other issues so beware. Normally you should be able to go 50 to 100 hours.

Clip affects jetting between 1/4 throttle and just below full throttle but.... I experiment first by moving the clip two positions closer to the top/flat and see if that makes a change for the better, Whiule you have the needle out to move the clip, make a note of the code on it.

Thanks, yeah, I was a little suprised on the valves, but he said only one was very slightly out of adjustment. As far as the needle goes-I thought maybe lowering the needle is what I should do since it has that flat spot, and that would seem more like a lean issue, and lowering the clip will richen it. But you might be right. I guess I'll look at the plug first and then decide from there.

First get a new plug, don't clean it, start from there?

Call JD Jetting, quick and easy. Tell them what you are experiencing they will get you straight the first time. They are awesome. Don't know what your valves have to do with 3/4 throttle bogs. Its in your jetting.

I worked on it today, and it's running great. It had a 165 main jet, and I changed it to a 168. It felt exactly the same after doing that so I moved the clip down one. The clip is now 5 down from the top. That's what it needed. It now runs crisp everywhere. I ride between 500-4500 feet. Temperature is generally anywhere from 40-85 degrees depending on the time of year. I've only had it at 500 feet so far and about 60 degrees so I'm hoping it runs good in elevation and colder weather.

I put a new plug in also-didn't feel any different until I moved the clip down one spot. But, the plug was massively rusted at the base-obviously from the previous owner washing the bike and not blowing that area out. The threads looked fine, and it wasn't hard to get out. It's a pain to take the tank off to pull the cap off the plug and blow it out, but I'll be doing that from now on. My local shop owner suggested spraying contact cleaner down there and blowing it out with the compressor before removing the plug-I'm glad I did! It's kind of cool that the outside cylinder wall has a little hole for the contact cleaner and debris to escape.

Thanks for the advice you guys gave me, I appreciate it. ~Happy riding~

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