2007 WR450F goes Flat/tight at high revs.


12 replies to this topic
  • skindiver

Posted November 25, 2009 - 02:44 AM

#1

HI

I bought a nice WR450 in mostly stock condition. Seller said it was stock tho he was second owner. I verified that the throttle stop was shortened and the pee pee was out of the exhaust entirely.

On my first ride I felt it had pretty good "go" until about two thirds through the rev range where the power and pull flattened off quite noticeably in each gear. Is this a trait of a stock WR450 ? Looking at dyno charts on thumpertalk the HP does flatten after 7000 or so and the torque goes south much earlier than that even.

I then did the grey wire only and the difference was chalk and cheese. The flattening out vanished and the bike pulled hard all the way to the limiter. No other problems except that while the bike had popped on decel a bit before the grey wire, it now popped, cracked like crazy after grey wire. (even between gear changes it barked)

Scared of leanness, I took it in to Yam and had him do GYTR AIS delete for backfiring and if lean any leaness would be adressed in the jetting changes he would do with the GYTR kit.

I also had him fit FMF Ti powercore slip-on thinking it would loosen up the top a bit.

I got on afterwards and was a bit dissapointed. My rip through the top 1/3 RPM range has disappeared and the flatness was there again. No more backfiring or popping though.

The midrange is impressive. More than before. It either stands up hard in first or second or digs a trench if you lay on the tank. I know that this is where you really want the power but just when you expect things to really get going it just flattens out again on top.

There is no real bogging, or any other other flat spots. It starts instantly and idles well. If you wick it hard from idle it will cut out, but when riding in real life i cannot ever forsee doing this. Yam warned me this happens when you do GYTR jetting. Its just not a problem to me though.

What he did on the jetting is as follows:

He left everything stock except two turns out on the fuel screw- he called it an air screw ? and changed the needle with clip in position 4 for the GYTR one with clip in position 4.
Believing the bike was stock, we both expected to find the stock non adjustable needle but rather found an adjustable needle in there, with clip in position 4 as well. He mumbled something about this adjustable needle being supplied with the bike when new.

Shouldn't the main have been changed with the needle change ?

Any ideas on why my new found top end 'go' got up and went ?

Appreciate any comments.

Skin.

  • Krannie McKranface

Posted November 25, 2009 - 06:34 AM

#2

Open up the airbox, put in a JD Jet kit (bigger main, pilot, better needle taper) and enjoy it.

  • Butta

Posted November 25, 2009 - 07:33 AM

#3

^x2..... it amazes me how the "professionals" at the shops conduct jetting changes. All the mods, AND an aftermarket pipe will definitely require a bigger main, at the least.

  • GuyGraham

Posted November 26, 2009 - 04:41 AM

#4

Verfiy what size mian jet you have

Should be 168

If 160 its too lean, and 175 its too rich
160 is std in the UK, 175 is supplied in a little bag for the owner to fit

  • skindiver

Posted November 26, 2009 - 07:40 AM

#5

Thanks guys.
The manual says 162 is stock. Dealer says he left it stock. I am going to open it up and see for myself what is in there. Dealer says i can get to the main by taking off big bolt on the bottom of the carb without stripping the whole bike.
I'm going to try look tonight. Will post what i find tomorrow.
Meanwhile the manual says that a rich condition at full throttle manifests as slow speed pick up. but a lean condition at full throttle manifests as a hard "breathing" engine. Both are rectified by going up or down on the main. But what the hell is a hard "breathing" engine ?

Skin.

  • skindiver

Posted November 26, 2009 - 10:26 PM

#6

Its a 162 main in there right now.
My riding alt is 5500ft and it hot summer.

regards
Skin.

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  • chevytrkn1

Posted November 27, 2009 - 04:39 PM

#7

I would go the jd jetting kit way myself. Mines an 07. All the free mods, Dr.D full exhaust with twin air filter and jd jetting. Thing rips and never hesitates or misses at all

  • Krannie McKranface

Posted November 27, 2009 - 04:41 PM

#8

Its a 162 main in there right now.
My riding alt is 5500ft and it hot summer.

regards
Skin.


The engine is an air pump. Fuel is added to the air at a mixture that should stay the same, throughout the rpm range, and at all throttle openings. This is accomplished by the jetting sizes.

By adding a pipe and opening the airbox, you have dramatically leaned out the engine (which is already very lean stock).

You must rotate the carb, verify the size of the Main jet and the Pilot jet, and put the correct sizes in. Once you do that, you need to remove the tank, rotate the carb the other way, and change the needle, so you get a better transition from idle to pilot.

It's all in the 'stickies' at the top of the forum.

  • wr450fLee

Posted November 29, 2009 - 04:42 AM

#9

I have owned a Uk wr450f 07 since new, I have opened out the air box and installed a dep s7 header and silencer, removed the AIS and grey wire. I have spoke to my dealer about re-jetting and he said you will be fine with the stock jet?

Is this correct on a Uk model?

  • GuyGraham

Posted November 29, 2009 - 10:38 AM

#10

I have owned a Uk wr450f 07 since new, I have opened out the air box and installed a dep s7 header and silencer, removed the AIS and grey wire. I have spoke to my dealer about re-jetting and he said you will be fine with the stock jet?

Is this correct on a Uk model?


not with the 160 it comes with, out of the showroom

It may have the 175 in it, that comes in the plastic bag (along with the other needle)

You need to verify what main and what needle are currently in it

  • wr450fLee

Posted December 06, 2009 - 04:04 AM

#11

Well I owned the bike since new but purchased it off uk dealer havent touched the carb since, It has become more powerful since the mods but not as muchas id of thought. it bogs wen opening up throttle quickly, I am assuming cos too much air intake but not enough fuel?

I will tackle the dreded strip down of the carb and see whats in there

  • Macsplace

Posted December 06, 2009 - 10:13 AM

#12

Sounds like you need one size larger on the main jet. When my 07 was lean had a 162 it would flatten abruptly on top and when it was a little rich 168 it would kind of hit a wall on top like it wanted to continue to rev but couldnt.I have a 165 now and am happy with it. I am using Yamaha jets. Also everytime that I have changed the main I have had to change the needle clip position.

  • Krannie McKranface

Posted December 06, 2009 - 10:40 PM

#13

Read the stickies.
Read the stickies.
Read the stickies.

It's all in there.




 
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