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Leak Jet #40

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I have seen some posts about this in some threads but what is the bottom line with this thing. I read it comes stock in a WR but will it work in a YZF? Also what are the advantages/disadvantages with this thing? Lastly, how much does it cost. Thanks

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It sounds like you are the victim of misinformation. Leak jets are used in newer FCR carburetors to tune the duration of the accelerator pump squirt. Many sizes are available, because that gives you the flexibility to tune the bike to YOUR riding style and needs. Since both the YZF and WRF use the FCR carb, jets are interchangeable between them.

Testing by loads of people on this forum have found that a leak jet in the 40 range solves the bog problem for most, but NOT FOR EVERYBODY. Some require the leak jet soldered shut, and some take a 50 or 60. It depends on the bike, its modifications, and your riding style. A smaller leak jet forces more fuel into the venturi, and a larger leak jet flows more fuel back to the bowl, allowing less into the venturi. >This< link has a drawing and explanation on how it works.

The 40 leak jet does not come stock on the WR. Stock LJ on my 03 was a 90, and I'm not sure what stock on a YZF is, but they all have them, just not in the right size. So tuning the AP squirt with the leak jet will work on either the WR or the YZF.

The purpose of all of this is to tune the AP squirt so the bike doesn't bog when you whack the throttle wide open. It doesn't make the bike have more power, or more top end. It just eliminates that classic 4 stroke bog, if you get it tuned right. First you have to get the rest of your jetting in good shape, then tune the AP using the leak jet.

They cost 5-10$ each depending on how big a crook your dealer is. Jet part numbers are here:

http://www.thumperfaq.com/yamaha_oem.htm

Be sure and take the part numbers with you when you go to the dealer, they won't even know what it is.

Search this forum for "leak jet", "bog", "AP" and "squirt", and read up in the FAQ for the full story.

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