WR450 Jetting issues

I have done my homework by searching through previous threads, and haven't come up with a solution yet. I purchased an 07 wr450f a couple months ago, and have been trying to get the jetting right every since. I purchased a Demissions kit, and Fast cap from F2racing.com, along with a promoto billet silent insert. Although the instructions for my demissions kit was very detailed, something still isn't quite right, and it's been trial and error every since. I currently ride between the elevations of 1000-3000 ft. The kit recomended a 168 main, Silver needle at 3rd position from top, stock pilot, fuel screw 1, 1/2-2 1/2 turns out, and #50 leak jet. I used the stock 162 main, and everything else as described above, and the bike ran well until I held the throttle at consistent throttle openings. Meaning, trying to maintain the same speed in one particular gear for an extended time. It sputters, and the power seems to cut out until I give it more throttle. If I crack the throttle wide open it responds well, or if I vary the speed through trails it seems to respond well. It's just gravel roads and pavement sections that I notice it. I tried changing needle positions from the 2nd position to the 4th position with know improvement. I changed the Main from the 162, to the 155 thinking I was running to rich. no luck. I again tried adjusting needle positions-no luck. Someone on this site recommended a #40 leak jet. Would this help me? Also, some mentioned running a 170 Main and a #48 leak jet with good success, but they were riding mostly desert. I also forgot to mension that if a close the throttle abruptly it backfires, unless I'm holding the clutch lever in. Thanks for yor time


48 Pilot

40 Leak

As the seasons change I adjust needle position and switch main 168/170.:ride:

I appreciate your input, I'll give it a shot.


The stutter at steady throttle is your TPS. This is normal. If you want to get rid of it, disable the TPS.

The back fire is most likely the AIS (unless removed) or due to the ACV.

Solution- remove the AIS and/or disable the ACV in the open position.

You did not mention it, but did you do the AP mod with the thick O-ring?

Hope this helps,


I spoke once again with F2racing. net, and there was a small piece that I didn't install, that supposedly doesn't come with the GYTR kit. There is supposed to be a 3/4 " plug that is supposed to be installed before the AIS block plate. The GYTR kit dosen't have this I guess. I somehow overlooked it. I hope this contributes to the problem. F2racing has been really good at walking me through this process. I simpily overlooked it. So I have eliminated the SMOG pump (AIS), but haven't tried the AP upgrade. Thanks for the info. I'm going to try that after installing this plug I overlooked.


Hi there my 07 wr450 also stutters at steady throttle openings, adjusted the ais needle from #4 clip to #3 clip and all of it disapeared bike runs strong at any throttle position.Oh and it does take the stutter away when you disconnect the tps but you also lose some response on fast aceleration!

My bike does the same thing. I have the ais kit from gytr. What other part is f2racing.net talking about so i can get it taking care of?

Is the power loss really noticable? My manual states that disconnecting the TPS will result in diminished engine performance if disconnected and then reconnected without replacing the TPS. What method did you use to disconnect it? Is this mod worth the decreased performance?


The TPS on this bike is a real pain in the ass if you want to do any road riding. There have been many posts about it. And you can find some solutions, but I have yet to find an acceptable one.

Search TPS Adjustment

Read the manual for the adjustment procedure.

Adjust the TPS to the high voltage within the acceptable range (at closed throttle) stated in the manual.

This will significantlly lessen the stutter. It may not eliminate it but it will almost eliminate it except for slight stutter on the highway at steady low throttle.:thumbsup:

The Stutter is an ignition timing issue. These bike were designed for the dirt or continuiously variable throttle. Not the street (very stable slow throttle opening):ride:

Disconnecting the TPS will give you a base or RPM only ignition timing map. adding Throttle Position to the map makes a three dimensional ignition map using TPS to indicate a "load relationship":applause:

Disconnecting the TPS will give you a base or RPM only ignition timing map. adding Throttle Position to the map makes a three dimensional ignition map using TPS to indicate a "load relationship":applause:

How much performance can one expect to lose with just the "base or RPM" timing, as opposed to having the three dimensional map?

I don't know excatlly how much power you will lose it is noticable.

However the power you loose will be less of an issue on the street than in the dirt.

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