what is optimum jetting for 07 yz450 and white brothers pro


28 replies to this topic
  • Family Man

Posted January 19, 2008 - 11:07 PM

#1

The directions that came with the WB Aluminum pro said for optimum performance use the stok jetting for an 06 yz450 but it doesnt say for the 07. Is the jetting the same for both bikes? If not what is the baseline jetting for the 07 and WB aluminum Pro. I'm around sea level to 2000 feet.

  • motoscotty

Posted January 20, 2008 - 04:38 PM

#2

Try 165 or 168 on the main 48 pilot I did not touch the needle and put a 55 leak jet.You will have to mess with the fuel screw a little1.75-2 out, mine runs exc.with theese settings..:

  • Family Man

Posted January 21, 2008 - 06:07 PM

#3

I put a 165 main jet in, it came with the bike and it helped, no more acceleration popping, have to order the other jets. What elevation are you at/around?

  • Family Man

Posted January 21, 2008 - 06:19 PM

#4

It's to bad White brothers dosn't list the jetting specs for the 07 with the installation directions, would make it alot easier. I called their phone number from the WB web site and it said They where "shutting down their order of opperations, effective imediatley;" what ever that means?

  • ktmburty22

Posted January 22, 2008 - 02:34 AM

#5

hey there family man,i dont know if this will help you at all,but my WB aluminium pro came with jetting specs at 162 main for sea level every thing else stock,bike runs sweet as,but its an 08,so sorry if thats no good to you,i thought you might like to know

  • Ga426owner

Posted January 22, 2008 - 05:33 AM

#6

jetting specs will be different for every altitude and every temp and humidity climate

  • blue22

Posted January 22, 2008 - 10:36 PM

#7

I don't know if anyone has said this yet, but White Bros. is no longer going to be in business. They are completely done manufacturing pipes.

  • Ga426owner

Posted January 23, 2008 - 09:21 AM

#8

I don't know if anyone has said this yet, but White Bros. is no longer going to be in business. They are completely done manufacturing pipes.


interesting please elaborate.....as the website is fully functioning

  • Family Man

Posted January 23, 2008 - 02:37 PM

#9

yeah I bet the ?WB pipe will go on clearence too. Right after I bought mine. oh well I like the pipe alot, anyways. To bad WB went under, they made some sweet products.

  • Family Man

Posted March 02, 2008 - 09:40 PM

#10

I put a 165 main in and I cant notice much of a differnce over the 160. except I heard my first backfire, although it was only one. Im at around seal level to probley 3000. what jetting do you guys reccomend? I have the fuel screw at 2 turns out from all the way turned in. I know the stock jetting is for the stock pipe and there is a big difference between the flow of the WB Pro verses the stock pipe, so I am thinking that it could benifit from larger jets... What do you think?

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  • grayracer513

Posted March 02, 2008 - 09:56 PM

#11

... there is a big difference between the flow of the WB Pro verses the stock pipe, so I am thinking that it could benifit from larger jets... What do you think?

I think that both of these are misconceptions; common, but fallacious, nevertheless.

There are no flow problems with the stock pipe. It is not restrictive in any real way. It is tuned for a specific result, and uses a distinctly stepped header and a small outlet diameter.

Pipes that have larger than stock muffler cores quite often end up needing leaner jetting, especially at part throttle.

Start by scrolling through the jetting sticky to see if someone else has a similar setup:

http://www.thumperta...ad.php?t=248849

If not, get your pilot jetting right:

http://www.thumperta...ad.php?t=327405

...then get your main jet figured out, and work from there.

  • Family Man

Posted March 02, 2008 - 10:33 PM

#12

I would think that a larger hole allows more air to pass letting the engine breath better? Could you ellaborate on this. Once I put the aluminum pro on my bike I did notice a substantal differance in the bikes power, more snap and revs. When I compare the stock exhaust to the WB I find it hard to beleave that it wouldn't exhale better. Also, Gray are you saying that larger jetting may not be required? Its easy to get confused by all of the conflicting information out there. Im new to jetting, but trying to learn. Thanks for the info.

  • Family Man

Posted March 02, 2008 - 11:10 PM

#13

Do you think a 165 main is in the ballpark, or just leave it stock 160? I dont think I need a bigger PJ because my fuel screw is a 2 turns and the pilot circuit guide say not to change it unless its more than 3 turns out or less than 1 turn in.

  • grayracer513

Posted March 03, 2008 - 08:08 AM

#14

Do you think a 165 main is in the ballpark, or just leave it stock 160? I dont think I need a bigger PJ because my fuel screw is a 2 turns and the pilot circuit guide say not to change it unless its more than 3 turns out or less than 1 turn in.

The stock pilot in an '07 is a 45, and that should be close. Try the 165 and see how it works.

I would think that a larger hole allows more air to pass letting the engine breath better? Could you ellaborate on this. Once I put the aluminum pro on my bike I did notice a substantal differance in the bikes power, more snap and revs. When I compare the stock exhaust to the WB I find it hard to beleave that it wouldn't exhale better. Also, Gray are you saying that larger jetting may not be required? Its easy to get confused by all of the conflicting information out there. Im new to jetting, but trying to learn. Thanks for the info.

If an exhaust system was a simple matter of how much gas volume you could run through the pipe, then all performance systems would be 3" tubing from one end to the other. But that is not the case. Racing exhaust systems are more complex than that, and it is actually true that there is an upper limit to header size that an engine can run and produce optimum power with.

Picture the chain of events in slow motion. The exhaust valve opens the relatively very high pressure combustion chamber to the relatively low pressure header, and as this happens, a pressure wave begins traveling down the pipe. The "wave" occurs because gas is compressible, and the entire pipe does not rise to the pressure at the exhaust port instantaneously. Rather, the pressure starts there and moves along the pipe very much like the compressed coils of a "Slinky" spring toy will when quickly compressed a short way. The wave travels at about the speed of sound, and when it reaches the end of the pipe, it produces a negative pressure (partial vacuum) that is "reflected" back toward the port, and will help draw out the last bit of exhaust and draw in the first bit of air/fuel, but again, only within a narrow range of operating speeds. Bear in mind, all of this happens in about one half a crank revolution

Besides, in looking at the stock exhaust, and realizing that it is open from one end to the other, do you think that when you release a burst of less than a half liter of compressed gas into one end that there would be any resistance to it moving to the other end freely?

Even if the exhaust were a simple matter of making it bigger to make it better, what would the result be? How would it make more power? Nothing in the exhaust will produce any power at all, regardless of what we do with it (apart from using the pressure to drive a turbo). The result of a more efficient exhaust system is an increase in the flow in the intake. But what happens when the intake air flow rises? The strength of the vacuum signal that raises fuel through the jets increases, and depending on the particular carb and engine, that can cause too much fuel to flow through the jet into the air stream, and make it necessary to reduce the jet size.

This is exactly what happened with my YZ250F when we put a WB R4 on it. The main was OK at full throttle, but the needle had to be replaced to get the part throttle right.

  • Family Man

Posted March 03, 2008 - 01:58 PM

#15

what do think about using a 155 main jet than instead of the 160? I have noticed that the bikes power feels alittle crisper with the 160 as opposed to the 165 but its pretty hard for me to tell the differnce between the two.

  • grayracer513

Posted March 03, 2008 - 02:16 PM

#16

My reflex is to think that unless you ride most of the time at 6000 feet or more, 155 would be smallish.

What's your normal operating altitude?

  • Family Man

Posted March 03, 2008 - 04:02 PM

#17

around 1400-3000 feet most of the time. Northern Ca

  • todds924

Posted March 03, 2008 - 09:24 PM

#18

around 1400-3000 feet most of the time. Northern Ca


Try this..........162 main........45 pilot.....2 1/4 turns on the fuel screw....Keep the stock NFLR needle.....also switch to a 50 leak jet. I can almost guarantee that will be really close to perfect for your altitude and pipe configuration.

  • yz250o2

Posted March 04, 2008 - 01:43 AM

#19

I have the 08 yz450 w/ the white bros aluminum pro. Maybe Ive been wrong all along about going to richer jets. Maybe I need to go leaner......I have deaccel popping out the ass. I even have a 50 pilot and it didn't help. So to me Maybe I need to go leaner.????

  • Family Man

Posted March 04, 2008 - 09:44 AM

#20

try confirming your pilot circuit.





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