1/2 to Full Throttle Problem - 08WR450

[themaskcabana]

Sorry guys, I search every where and I couldn't seem to find what I was looking for. Maybe you guys can help me out. Any help would be much appreciated.

I just bought a new 2008 WR450, this is what I have done.

Throttle stop removed

Grey wire cut

Opened airbox

AIS has NOT been removed

TPS still connected

Stock pipe with peashooter removed

JD jetting kit

Main 168 - I have gone one up and one down and it stutters. 168 is the best.

Pilot 45 - I went one up to 48 and didn't like it. So I went back down to 45

Red needle with clip in 4th position

Fuel Screw 1.5 turns out

R&D Power Pump with leak jet set to 40

PowerNow & PowerPlus

My Problem:

Off the low end it pulls great, between 0 and 1/2 throttle I have plenty of power, it pulls strong. Between 1/2 and Full throttle it just stops pulling, it's like the powerband just quits at half throttle position and doesn't want to go any higher. It doesn't really bog, it does seem to stutter a little bit, but not much at all. However, more than anything it just stops pulling as soon as I get to 1/2 throttle. Almost as if it is choked up.

My old WR 2003 pulled strong all the way through the gear.

Any ideas fellas?

[OUTERLIMITS]

You didn't mention the throttle stop screw. You need the YZ unit or cut yours down.

[themaskcabana]

You didn't mention the throttle stop screw. You need the YZ unit or cut yours down.

Forgot about that, sorry. I edited to include throttle stop. Thanks for the post though

[SXP]

A 168 main might be too rich with just the pea shooter removed. To verify, remove the entire "spout" and replace the end cap. Ride it and see if the response is improved from 1/2 to full throttle which is when the bike is on the main jet. If this cures it, then replace the "spout" with a GYTR or PMB insert.

[123BigcoopDawg576]

A 168 main might be too rich with just the pea shooter removed. To verify, remove the entire "spout" and replace the end cap. Ride it and see if the response is improved from 1/2 to full throttle which is when the bike is on the main jet. If this cures it, then replace the "spout" with a GYTR or PMB insert.

im thinking that with the stock exhuast (header and muffler) this is your problem especially with your 168 main.

im running the same main but i have an FMF 4.1 slip-on and an 08 yz header and my bike never stops pulling:ride:

[themaskcabana]

Thanks guys, I had the same feeling but wanted to confirm it. I thought that it might be the exhaust choking up the engine, but figured I would get some ideas from you guys.

[themaskcabana]

I removed the insert in the exhaust to see if the bike would run better, and it runs a hella of a lot better. The exhaust was definitely choking up the engine and my jetting was too rich for the stock exhaust. For the most part it actually pulls strong through most of the gear. It still doesn't pull real strong from a little more than 3/4 to full, but I think it could be the header pipe as well. I probably need a whole new setup. Maybe a used yz450 pipe will work. I think the jetting is great, but it still runs a little rich as it's gunging up my pipe.

Do you guys think with the a yz450 set up and my current jetting that it should be spot on for the most part? Do you think the header is choking up my bike as well?

Thanks guys!

R

[William1]

Remove the Power Now stuff, they are band aids instead of fixes and do restrict the carb. Check your AP squirt timing instead.

Did you try a fresh plug?

Might not be a bad idea to confirm cam timing is correct too.

[SXP]

The smaller diameter WR header is optimized for low end torque. A YZ header and pipe will certainly open things up on top with a some sacrifice at lower rpms. Depends on your riding style I guess - your call.

[themaskcabana]

Remove the Power Now stuff, they are band aids instead of fixes and do restrict the carb. Check your AP squirt timing instead.

Did you try a fresh plug?

Might not be a bad idea to confirm cam timing is correct too.

Really? You think the PowerNow and PowerPlus does more harm than good? I haven't tried the AP squirt, I'm not even sure how to check it? I did get the R&D power pump with the stiffer spring so theres no delay. My throttle response seems to be spot on. Before it was shitty between 1/2 and full throttle, but with removing the exhaust insert there was a huge improvement so I figured that's the way I should head. Though as I said theres still a slight power band stand still between a little more than 3/4 and full, but still a huge improvement.

Didn't try a new plug. I figured because I have only ridden it twice, the plug should be good, but my jetting was way to rich originally so it may be a good idea.

[themaskcabana]

The smaller diameter WR header is optimized for low end torque. A YZ header and pipe will certainly open things up on top with a some sacrifice at lower rpms. Depends on your riding style I guess - your call.

No, I like the low end feel. I was just hoping for mid and high. I ride lots of trails, but sometimes go to the mx track as well.

[William1]

Yup, you have installed a restriction in the system using the PN devices. What they do is mask and compensate incorrect jetting, primarialy the

AP. Read about the O-Ring Mod and AP Tuning though since you have done the stiffer spring, ignore the oring parts.

I assume you have removed the snorkle and snorkle mounting plate to open the airbox.

I would try the needle on the 3rg clip and a 170 main jet too.

As you experiment, make only one change at a time, then test. If a change makes things worse, by doing them one at a time, you will know with absolute certainty what caused the change.

[themaskcabana]

Yup, you have installed a restriction in the system using the PN devices. What they do is mask and compensate incorrect jetting, primarialy the

AP. Read about the O-Ring Mod and AP Tuning though since you have done the stiffer spring, ignore the oring parts.

I assume you have removed the snorkle and snorkle mounting plate to open the airbox.

I would try the needle on the 3rg clip and a 170 main jet too.

As you experiment, make only one change at a time, then test. If a change makes things worse, by doing them one at a time, you will know with absolute certainty what caused the change.

Well, I'll give it a whirl. Everyone swore by the powernow system, and so I assumed it would be a great addition. It claims to make the airflow better, but I'll give it a try.

Yep, I did remove the snorkel. I did pretty much all the free mods except the AIS. I have the JD Jetting Kit, R&D Powerpump and the powernow system as you know.

Thanks for the info! I'll see what I can come up with.

Question: Just read your adjustment on the AP Squirt, nice read by the way, very well done. So essentially I want to barely and I emphasize barely miss the slide? Also will my leak jet have any baring on this?

[Mutu]

try red #3, or blue #2. stutter is rich.

[Fullbore4]

Probably the reason your running rich is because the Powernow induces much better air flow and a more effective venturi action (velocity up/ static pressure down). The powernow is great.....the powernow plus did nothing for my bike and may have hurt performance. On the exit side of the carb you want turbulence (velocity down/static pressure up) to help atomize the gas and the "plus" would tend to make flow more laminar. I took the plus off my bike. It sounds like you need to move the needle down or lean it out a bit more and maybe try a smaller main or put a pipe on it which would lean it out a bit.

[William1]

Yes, you want to set the AP to just barely moss the slide.

Leak jet affects a few things. Primarily, it affects the strength of the squirt. Secondly, it affects the duration of the squirt. At low rpm's (say below 5K) you need more fuel due to the low velocity of air flow that results from suddenly opening the slide. A leak jet 'leaks' fuel from the AP circuit, thereby causing the squirt to not be as strong and last as long. The Power Now attempts to 'fix' the issue by keeping the air velocity up. Which is fine if you do not go much above 1/2 throttle. Instead, a properly setup AP can do it without the device. If you st the AP up to completely eliminate any bog at slow speed, it is possible you may experience some bog at high rpm's (say 9K+) due to the AP supplying too much fuel. YZ's and WR's are theoretically race bikes and were designed to be running at high rpm all the time and accordingly, are set up with an early squirt and large leak jet. In real life, most of the owners do not ride th way and therefore the bikes need a little "attitude adjustment".

[themaskcabana]

Thanks guys, this is great information! Only at thumpertalk. I think I have learned more in the last two days than I have in the last ten years...haha.

You guys are awesome!

I'll get on that AP and time it just to miss the slide. I'll be back to report.

[themaskcabana]

William1,

Thanks as always for your input. I tried adjusting my AP, but I'm a little lost. I pulled the screw out counterclockwise... First 1 turn, then 2, then 3, then 4 just to see if the squirt would hit the slide...nothing. The squirt still won't hit the slide. Is this because I have the stiffer spring?

I will say a couple of things. Once I changed the exhaust, it was a 100% better. No bog and ran great. However, I just wanted to check to make sure my ap timing was correct. Before I adjusted it, it looked like it barely missed the slide, but I went ahead and adjusted anyways to see if it would hit the slide and then back off half a turn or so, but as I said above I turned it out 4 turns and nothing.

Is this explainable? How do I make sure its adjusted perfectly if it won't hit the slide.

Thanks as always for any input!

Yes, you want to set the AP to just barely moss the slide.

Leak jet affects a few things. Primarily, it affects the strength of the squirt. Secondly, it affects the duration of the squirt. At low rpm's (say below 5K) you need more fuel due to the low velocity of air flow that results from suddenly opening the slide. A leak jet 'leaks' fuel from the AP circuit, thereby causing the squirt to not be as strong and last as long. The Power Now attempts to 'fix' the issue by keeping the air velocity up. Which is fine if you do not go much above 1/2 throttle. Instead, a properly setup AP can do it without the device. If you st the AP up to completely eliminate any bog at slow speed, it is possible you may experience some bog at high rpm's (say 9K+) due to the AP supplying too much fuel. YZ's and WR's are theoretically race bikes and were designed to be running at high rpm all the time and accordingly, are set up with an early squirt and large leak jet. In real life, most of the owners do not ride th way and therefore the bikes need a little "attitude adjustment".

[themaskcabana]

William1,

Thanks as always for your input. I tried adjusting my AP, but I'm a little lost. I pulled the screw out counterclockwise... First 1 turn, then 2, then 3, then 4 just to see if the squirt would hit the slide...nothing. The squirt still won't hit the slide. Is this because I have the stiffer spring?

I will say a couple of things. Once I changed the exhaust, it was a 100% better. No bog and ran great. However, I just wanted to check to make sure my ap timing was correct. Before I adjusted it, it looked like it barely missed the slide, but I went ahead and adjusted anyways to see if it would hit the slide and then back off half a turn or so, but as I said above I turned it out 4 turns and nothing.

Is this explainable? How do I make sure its adjusted perfectly if it won't hit the slide.

Thanks as always for any input!

bump, just trying to get an answer to why my ap is not hitting the slide even though I have pulled the screw out counterclockwise about as much as you can go.

Any ideas?

[William1]

I suggest returning the AP adjstment back to where it was before. If the PN stuff has been pulled, you have no bog, have the ALJ set to be as large a LJ as possible and have no bog, then you are probably fine.

A lot of guys read about a 'fix' and try to apply it even though they do not have the 'problem'. You know the old saying 'Don't try to fix it is it anin't broke'.

Sorry I missed you Q......