what is optimum jetting for 07 yz450 and white brothers pro

28 replies to this topic
  • yz250o2

Posted March 07, 2008 - 01:40 AM


I did. I think its a 48.......is best. family man you running that WB header that came with the system? Im not. I like the stock header powerband a little better. The Wb header either hits too hard or has to much bottom.

O and how are you sealing the exhaust? I dont really think that would be a problem tho.

  • Family Man

Posted March 07, 2008 - 11:59 PM


The exhaust seals great no problems. The stock header is much shorter than the long header that came with the aluminum pro. Never thought of using the stocker? The aftermarket wb didnt come with a heat sheild which means it burns through your riding gear, I kinda liked/miss the heat sheild. However, I like what the wb aluminum pro did for my bikes power, alot. I read that the header is majorly responisble for the bikes performance. Im running the whole system, I like the hit/power. Im thinking of trying the jets todd sugested, just have to order them. Do you think that going from the stock 55 leak jet to a 50 will make a noticable diffence?

  • Family Man

Posted March 08, 2008 - 12:45 AM


Maybe the stock header doesnt go into the wb exhaust far enough and its leaking there that could be causing your bike to pop like crazy. You might be able to seal it up with high temp silicone.

  • Family Man

Posted March 14, 2008 - 05:23 PM


I just placed an order for a 162 main, I was going to place an order for the 50 leak jet too but the parts manager said that stock is 55. I have a stock accelerator pump, should I still give the leaner 50 leak jet a try?

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  • grayracer513

Posted March 14, 2008 - 07:59 PM


A 50 leak jet is richer than a 55, and only has an effect on the amount of fuel delivered by the accelerator pump while the throttle is actually opening.


  • Family Man

Posted March 14, 2008 - 10:26 PM


Do you think that changing the Leak jet to a 50 is a worthrile mod on a 2007 in Northern Ca, say approx sea level to 4000 feet. From the link you posted Im thinking that a 50 leak jet instead of a 55 may mean a crisper throtle response? I got confused as to whether or not a 50 leak jet was richer than a 55 because when I went into the dealer I was told that...

  • grayracer513

Posted March 15, 2008 - 09:28 AM


The jet will not help at all unless the problem is that the AP shot is too small now.

  • Family Man

Posted March 15, 2008 - 12:09 PM


how could you tell if the leak jet was too small, from ridding?

  • grayracer513

Posted March 15, 2008 - 03:12 PM


If a leak jet is too small, an engine will "load up" or act rich during maneuvers that require a lot of throttle movement without any real sudden changes in intake vacuum, as in working through a tight trail section. Under these circumstances, the engine does not need the extra fuel delivered by the accelerator pump, but with too small a jet, it will be delivered anyway, causing a too rich condition, and engine performance that is generally uncrisp. With a big enough leak jet, the fuel output from the pump is leaked away into the float bowl under less vigorous throttle activity, and never enters the airstream.

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