07 WR459 - re-jet or don't, or do, don't...wait

[crackjacker]

I have read a few other threads, and one thing that doesn't quite get answered for me is whether or not I should re-jet with only these mods:

Shorter Throttle Stop

Grey Wire

Snorkel Removed from Airbox

Smallest stuffer (riveted) removed from pipe

I also have an adjustable fuel screw in the carb. The bike seems to run great, but the couple posts about doing damage to the bike from running too lean has gotten me a little paranoid. I just put in a new plug last weekend, and removed the grey wire this week, so I won't have a chance to check the plug until after this weekend. What do you guys think? ?

Thanks!

[FORMA MOTO]

The bike comes lean from the factory, so jetting is needed when new.

Add more air in/out (airbox and pipe mod) and now it is even more lean.

Buy a jetting kit (James Dean) and fix er up. It will run better, faster, stronger.

[crackjacker]

The bike comes lean from the factory, so jetting is needed when new.

Add more air in/out (airbox and pipe mod) and now it is even more lean.

Buy a jetting kit (James Dean) and fix er up. It will run better, faster, stronger.

Thanks for the info. Now, I'm only asking, but wouldn't the adjustable fuel screw take care of this? The bike runs great, and I am really not looking for more power, and certainly not faster, lol. My main concern is reliability. When I pulled my last plug, it actually had a look that suggested a little rich. (this was before removing grey wire) I mainly want to be sure nothing is going on in the carb that I can't see that might be not good.

Thanks again man, appreciate it!

[Demo_Slug]

Thanks for the info. Now, I'm only asking, but wouldn't the adjustable fuel screw take care of this? The bike runs great, and I am really not looking for more power, and certainly not faster, lol. My main concern is reliability. When I pulled my last plug, it actually had a look that suggested a little rich. (this was before removing grey wire) I mainly want to be sure nothing is going on in the carb that I can't see that might be not good.

Thanks again man, appreciate it!

Maybe I misread your question. So forgive me if I’m point something simple out.

But a fuel screw and the circuit it adjusts is only used near idle. the amount of gas that flows thru it is very very small compared to the amount of gas that flows thru the main jet at full throttle.

And I’m going to be very very simplistic here. At small throttle the gas mixed with the air going thru the carburetor is metered by the fuel screw. once the throttle slide is open the second circuit, the needle, starts adding gas too. Somewhere close to 75% the needle pulls out and then the main jet is adding lots of gas. So all of them have to be sized to match each other.

[crackjacker]

Maybe I misread your question. So forgive me if I’m point something simple out.

But a fuel screw and the circuit it adjusts is only used near idle. the amount of gas that flows thru it is very very small compared to the amount of gas that flows thru the main jet at full throttle.

And I’m going to be very very simplistic here. At small throttle the gas mixed with the air going thru the carburetor is metered by the fuel screw. once the throttle slide is open the second circuit, the needle, starts adding gas too. Somewhere close to 75% the needle pulls out and then the main jet is adding lots of gas. So all of them have to be sized to match each other.

Great answer man. Much appreciated. So, if I can, let me get your opinion. With the couple mods that I have made, and no intention of getting a larger pipe or anything like that, do you think re-jetting is necessary?

[Dirtskills]

In the May 2009 Dirt Rider they say the stock jetting is close to perfect.

they also did your same mods minus the fuel screw.. dirtrider.com 450 offroad shootout..

[crackjacker]

In the May 2009 Dirt Rider they say the stock jetting is close to perfect.

they also did your same mods minus the fuel screw.. dirtrider.com 450 offroad shootout..

you know what's funny? I read that in the August 2007 Offroad Shootout. They also did the same exact mods. I'm starting to think that if it's running great and I'm happy, I'm just going to keep it the way it is and keep an eye on the plug.

Thanks for the info!

[02WR426Cali]

Whoa you got a big bore 459 from the factory? Haha I'm just kidding but someone had to say something =) It's just a joke don't get all worked up people. I would recomend a JD jet kit as well, you won't go wrong with one of those they work great.

[FORMA MOTO]

IMHO: Most of the magazines (all?) in 2007 did not test a stock bike. They removed the throttle stop, changed the main and the needle. Dirt bike mag tells you when they do this, some of the others don't. I believe in 2008 the bike came jetted richer from Yamaha.

Oh, and checking your plug color to determine jetting is a fallacy: You would have to use race gas (no impurities) and run the bike wide open on a new plug, then cut the throttle and press the kill button. And that would only cover the main jet. From my understanding, fuel quality affects plug color more than you know. Most riders are never full on the main jet, and it is usually the needle that is too rich if there is a rich condition that would affect the plug color. Too rich as in too quick of a taper or high a position on the clip. In my opinion.

[SXP]

Oh, and checking your plug color to determine jetting is a fallacy: You would have to use race gas (no impurities) and run the bike wide open on a new plug, then cut the throttle and press the kill button. And that would only cover the main jet. From my understanding, fuel quality affects plug color more than you know. Most riders are never full on the main jet, and it is usually the needle that is too rich if there is a rich condition that would affect the plug color. Too rich as in too quick of a taper or high a position on the clip. In my opinion.

I didn't think the classic "plug check" procedure applied to four strokes. Always thought that was a two stroke thing:excuseme:

Am I wrong here?

[crackjacker]

I didn't think the classic "plug check" procedure applied to four strokes. Always thought that was a two stroke thing:excuseme:

Am I wrong here?

It does. They just don't foul as quickly. But if you are burning too much fuel in the chamber, carbon and all that builds up thus causing a foul.

Anyway, regarding my issue, what I'm going to do is find a long, long stretch of road, heading into the deepest bowels of the grand canyon, and hit it flat out Thelma and Louise style. Jetting will be a moot point after that. lol

[crackjacker]

IMHO: Most of the magazines (all?) in 2007 did not test a stock bike. They removed the throttle stop, changed the main and the needle. Dirt bike mag tells you when they do this, some of the others don't. I believe in 2008 the bike came jetted richer from Yamaha.

Oh, and checking your plug color to determine jetting is a fallacy: You would have to use race gas (no impurities) and run the bike wide open on a new plug, then cut the throttle and press the kill button. And that would only cover the main jet. From my understanding, fuel quality affects plug color more than you know. Most riders are never full on the main jet, and it is usually the needle that is too rich if there is a rich condition that would affect the plug color. Too rich as in too quick of a taper or high a position on the clip. In my opinion.

Dirt Rider specifically said, and I quote

"we left the stock jetting in the bike and did not mess with the AIS as it has no performance effect on the bike other than the lean popping noises in the exhaust."

I'm not saying that they are right and we are wrong, I'm just compiling different sources of info. I'm probably going to go ahead and re-jet just to be on the safe side, although the idea of the bike running even faster is not appealing to me.

Regarding checking the plug, I am going to respectfully disagree. From personal experience, I believe it does give a pretty good indication of the amount of fuel being burnt in the chamber, or lack thereof. Anyway, don't read too much into that, I respect your info, and appreciate it greatly!

Thanks!

[erickdj]

Dirt Rider specifically said, and I quote

"we left the stock jetting in the bike and did not mess with the AIS as it has no performance effect on the bike other than the lean popping noises in the exhaust."

I'm not saying that they are right and we are wrong, I'm just compiling different sources of info. I'm probably going to go ahead and re-jet just to be on the safe side, although the idea of the bike running even faster is not appealing to me.

Regarding checking the plug, I am going to respectfully disagree. From personal experience, I believe it does give a pretty good indication of the amount of fuel being burnt in the chamber, or lack thereof. Anyway, don't read too much into that, I respect your info, and appreciate it greatly!

Thanks!

I prefer to look at it this way: Magazines do one test, at one set of conditions (temps/elevation/etc). WR owners on this forum perform multiple tests all over the place with all kinds of variations. It's been proven more times than we can count, that the bikes are lean even when choked up from the factory. Opening up the intake/exhaust only makes matters worse. Like you said, it's not about going any faster, it's about making sure the engine is running the way it should and making sure it stays reliable. Jets are about $5 and an NFPP or NFLR needle are about $19. The worst that can happen by rejetting is spending about $30, leaving it running too lean on the other hand.... well, lets not get into how expensive that can get. In the end, it's up to you what you want to do.

[crackjacker]

I prefer to look at it this way: Magazines do one test, at one set of conditions (temps/elevation/etc). WR owners on this forum perform multiple tests all over the place with all kinds of variations. It's been proven more times than we can count, that the bikes are lean even when choked up from the factory. Opening up the intake/exhaust only makes matters worse. Like you said, it's not about going any faster, it's about making sure the engine is running the way it should and making sure it stays reliable. Jets are about $5 and an NFPP or NFLR needle are about $19. The worst that can happen by rejetting is spending about $30, leaving it running too lean on the other hand.... well, lets not get into how expensive that can get. In the end, it's up to you what you want to do.

yup. I just got done with my order from JD. Better safe than sorry. Hey,

THANKS EVERYONE!!!

you guys kick azz.

[Demo_Slug]

Great answer man. Much appreciated. So, if I can, let me get your opinion. With the couple mods that I have made, and no intention of getting a larger pipe or anything like that, do you think re-jetting is necessary?

I'm going to call jetting an art form or a skill. I've done my reading on the carb, so that I would know what each major part does, but I have no skill. ?