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marcoma

05 WR jetting question

13 posts in this topic

Hey Guys

So I took the plunge and bought a used '05 WR450 this weekend. When I tried it out, the jetting was pretty messed up. The previous owner said his dealership had rejet the bike following them fitting a Yoshimura pipe and header.

I decided to ensure all the free mods had been done to coincide with what he was telling me and found out the only other mod they did was the throttle stop screw. I set about trying the free mods - I cut the gray wire - I removed the snorkels and cut two holes in the side of the airbox - I checked the throttle stop screw had been cut (too much in fact) - I reversed the diaphram....then put it back after running the bike.....not sure if I have to block one hole, both holes, no holes, remove spring, whatever!

I'm currently waiting on an AIS kit. The pilot screw is an aftermarket item - it has an anodised red adjuster with white numbers (1-4) on it.

So after all that blog, heres my dilemma..... at about 1/4 throttle the revs are irratic. Sometimes it stalls, sometimes it overrevs. I've tried disconnecting the TPS and it makes no difference. On full throttle it sings along but anything below half is dodgy to say the least. I havent removed the carb yet to check what jets were changed by the dealer but if anyone has had the same issue as above, I'd be glad of a pointer as to what I need to do to fix it. I'd like to know if theres a specific jet that contributes to this?

Dunno if it makes any difference but I have a LOT of overrun (popping) when the throttle is shut off.

For the record, I ride in temperatures between 70 and 90 degrees at 1000-3000 feet altitude.

CHEERS - Marcoma

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.....and one more quickie - surely you should cut holes in the sidepanel if you've cut airbox holes, right? It seems a bit pointless cutting holes in the side of the airbox if you seal it back up with the sidepanel....

Somebody please clarify......

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sounds like a jetting issue rejet it per the indy jetting specs in the sticks at the top of the page. other then that your on the right track for uncorking this bad boy

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Fullbore4 - to quote the FAQ's

"Q: Why does my WR seem to miss when I hold the throttle steady in the 1/4 to 1/2 turn range?

A: That's your TPS (Throttle Position Sensor) doing it's job. Dirt bikes don't normally run with a steady throttle off road and they weren't designed too. Unplug it and see if the "miss" goes away. "

I already tried that and it didnt make any difference (see original post).

I was just wondering if a specific jet i.e. pilot, main, leak, etc was a contributing factor to the issue.

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Try this combo, 168 main jet, 48 pilot, pilot air screw 1.5 turns out. It should be close to running right with these jets. Get a YZF 450 needle from the Yamaha dealer, start with clip in 3rd groove from the top. The needle will clean up the bottom to mid range. If your Yosh pipe has a large open end cap you will need a 170 main. What I have told you here is the cheapest way to tune your 05 bike. The jet chart on TT works well for the older 450's not the 05. Power now for the carb if you want more low end snap. This base line works well and you can fine tune it to your taste. You need to undo what the dealer did to your bike! Good luck.

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No biggie - yeah I read thru that and found a few people riding in the same area and altitude as myself. I figure if I match those (which is pretty much what Desracer wrote) I should be on the right track. I also noticed another thread which stated that a blocked pilot jet may give simillar symptoms. I think I'll change mine (and all the others) just for the hell of it.

Happy days!

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I'm no expert but here's what I'd do.

1) Throttle stop too short - Replace with longer one so you don't take the chance of sticking the throttle wide open or wearing the throttle cables prematurely.

2) Gray wire - Make sure you have the correct grey wire cut by enlarging the pictures in this post:

http://www.thumperfaq.com/gray_wire.htm

(This could causes a slight misfire if it is still connected)

3) ACV diaphram - put back to stock configuration. No gain doing mod.

4) AIS kit - install asap. Eliminates most of backfiring on decel.

5) TPS - check setting with volt meter per service manual. You can get a copy of the service manual in pdf format from a link in this link

http://www.thumpertalk.com/forum/showthread.php?t=419006

Make sure the TPS is functional because it could cause the irratic firing at 1/4-1/2 throttle also.

6) Carb - Take out and clean. Check slide for any cracks. Make sure all vent lines are open and that you can blow air out the bowl vent tube. Set float per service manual.

6.5) Jets - First remove all jets and check for blockage. Use Indy's chart and start with those jets. Set the red "Zip-ty" Fuel Screw you have to 1-1/2 turns out from LIGHTLY bottoming out for starters.

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Check here for ACV mods. It sounds like you did method 8, which, if I remember correctly, blocks the ACV closed like the YZF. That would cause a very rich condition on the pilot circuit, which would cause the erratic 1/4 throttle performance. As someone mentioned, put it back to stock and it should run OK.

Of course, method 8 may block the ACV open, in which case I have it 100% backwards.

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I got tired of messing with the jetting at different elevations so I got a Edelbrock carb it' so easy to adjust but the best thing is I haven't had to:applause:

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UPDATE -

1) Throttle stop too short - Replace with longer one so you don't take the chance of sticking the throttle wide open or wearing the throttle cables prematurely.

CHECK

2) Gray wire - Make sure you have the correct grey wire cut by enlarging the pictures in this post:

CHECK

3) ACV diaphram - put back to stock configuration. No gain doing mod.

CHECK

4) AIS kit - install asap. Eliminates most of backfiring on decel.

CHECK - Did it today......ENORMOUS difference!

5) TPS - check setting with volt meter per service manual. You can get a copy of the service manual in pdf format from a link in this link

Next on my list....

Make sure the TPS is functional because it could cause the irratic firing at 1/4-1/2 throttle also.

6) Carb - Take out and clean. Check slide for any cracks. Make sure all vent lines are open and that you can blow air out the bowl vent tube. Set float per service manual.

See below

6.5) Jets - First remove all jets and check for blockage. Use Indy's chart and start with those jets. Set the red "Zip-ty" Fuel Screw you have to 1-1/2 turns out from LIGHTLY bottoming out for starters.

Ordered complete new set of jets today. I'm gonna go with the YZ adjustable needle with a 170 main, a 48 pilot and a 40 leak. I figure the float is set okay as a) I dont have any overflow problems and :D theres no fuel starvation on max throttle. If it aint broke....:worthy:

Thanks for the advice - good sound stuff!

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