2003 WR450 Jetting puzzle

This has been posted before and I have traded emails with Indy and JD. Still the confusion remains.

2003 WR450 with Pro Circuit 496 muffler, gray wire cut, YZ throttle, TPS disconnected. Started with 155/42/stock #4 and the bike had a mid range stutter when snapping throttle from 1/2 to full - roll on was fine

Followed recommendations and rejetted to:

168/42/ stock 4th = low throttle, low speed stutter / great midrange and WOT.

168/48/stock 4th = same (little worse) / great mid to WOT

168/45/ stock 4th = same

168/45/stock 3rd = still stutter

165/45/stock 3rd = same

170/45/JD blue #4 = worse

160/45/JD #4 = better but still not right

back to 155/42/ blue #4 = same as original.

I do not have a clue why this 2003 WR450 does not get the results that everyone else did with the 168/45/#4 jetting. :crazy:

Anyone experience this? Moded bike running better with closer to stock jetting?

Why are you changing the main jet when the needle is your problem?

Try the red needle #4 with 48 pilot and 168 main.

yeah, i tend to agree with Matty, it certainly points to the needle choice/position alright - but why disconnect the TPS ...?

secondly (and don't shoot me for being so blatantly obvious) a friend of mine disconnected the 'grey' wire on his '03 and it ran a lot like your's is sounding. It turned out the he disconnected the wrong wire (not exactly sure which one it was) - it still ran but similar to what you describe.

Try reconnecting the grey wire (and possibly the TPS) to eliminate these two as the possible culprits ...

i assume that your airbox has been opened up and you're using a 'twin-air' or similar filter also ?

just my 2c ... good luck

When all else fails I would blame the pipe. Not all pipes are tuned the same way and some just cant be jetted right. Try and swap mufflers with a buddy or put the stocker back on uncorked and see if that solves your problem. :crazy:

Why are you changing the main jet when the needle is your problem?

Try the red needle #4 with 48 pilot and 168 main.

that's exactly what I'm running and it runs excellent!

OK so everyone agrees that

I check the 'gray' wire mod and then

168

48

JD RED #4

Air box is open with UNI air filter. Temps are heading up, in the low 90s now, but this jetting, according to tables, should be ok up to 3500ft.

I don't have the stock muffler.

Good part is I sure have alot of practice taking off the carb plus have a lot of extra jets !

Temps are heading up, in the low 90s now...
Oh, there you go. Anything above 70 (tops) and you should be using the red needle.

PKCOF gets the Gold Star. I double checked the Grey/Gray wire mod and lo&behold it was still connected. I had asked the previous owner just last week and he said 'Yes' it was taped off. But I could not find anything taped off except the TPS connectors I found earlier.

I will re-jet according to the 168/48/ Red #4. TPS connected.

I hope we will now have an answer for 1/4 throttle stutter.

Thanks Indy and JD for answering my PMs.

Larry

PKCOF gets the Gold Star. I double checked the Grey/Gray wire mod and lo&behold it was still connected. I had asked the previous owner just last week and he said 'Yes' it was taped off. But I could not find anything taped off except the TPS connectors I found earlier.

I will re-jet according to the 168/48/ Red #4. TPS connected.

I hope we will now have an answer for 1/4 throttle stutter.

Thanks Indy and JD for answering my PMs.

Larry

I assume from your screen name that you live in Poway and are jetting for the local desert? If so a 168 main and a 48 pilot should be in the ballpark. I run either the blue needle on clip #3 or the red needle on clip #4. My '03 runs very clean with a blue #3 setting. The '04 has a YZ cam in it and that seems to make it a little more difficult to clean up the bottom so I generally run the red #4 setup on that bike. Generally if you have a stutter at 1/4 throttle it's because the mixture is too rich at the needle/pilot transition. Try leaning the pilot slightly and/or dropping the needle 1 clip. Oh yeah and ditch the stock needle!

hey Poway1464, glad that i was at least able to point you in the right direction (and my first 'gold star') - i have had quite a bit of help and feedback since i have joined TT and i have been able to fine tune my 450 to get it running just the way that i like ...

forums like this one are a bonus for us all !

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