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toofazt

Help...

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I have a '03 YZ450. I think it may be running lean. What are the symptoms of a lean YZ450? It pops A LOT during deceleration but I also have a Yoshimura exhaust that has a slip on part. How can I tell if it's leaking? The bike also has Yoshimura head work but I don't know to what extent if that matters? I've never swapped out jets or anything before, how hard is it? Does anyone have a good guide w/ pics for switching jets? I live in Southern California and ride in 60-85 degree weather, what jet size would be correct? Just trying to figure this bike out... Thanks, Steve.

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Yep, sounds lean and/or exhaust leak.

Yoshimura does not recommend any jetting changes for their systems aside from having the fuel screw out 1.5 turns. http://www.yoshimura-rd.com/jetting.asp

What is your elevation? Find out here: http://www.thumpertalk.com/forum/showthread.php?t=109238 Once you have your elevation we can probaly get you pretty close on jetting.

This will show you how to change your jets: http://www.thumpertalk.com/forum/showthread.php?t=445186

As far as a good way to check for an exhaust leak, I don't know...I'm going to leave that for somebody else.

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My elevation is 1300' - 2000'. The problem is, I don't know if my jetting is stock or what? I bought the bike already like this. So that means, screw it all the way in and then clock wise and then counter clock wise 1.5 turns? Thanks for you help so far!

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Well, just splitting the differences I went with 1600' and 72 deg. I **think** the '03 stock jetting is a 165 main jet and a 42 pilot jet. Based on your elevation and temp I would try a 162 main jet. Yes, I know that is leaner jetting than stock so I'm suspecting that a) the previous owner rejetted much leaner than stock and/or :ride: you have a pretty good exhaust leak causing the popping.

Yes, you are correct on adjusting the fuel screw.

Do you have an owners manual to verify what the stock jetting is? Also, it would be good for you to know which jets are installed right now.

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My elevation is 1300' - 2000'. The problem is, I don't know if my jetting is stock or what? I bought the bike already like this. So that means, screw it all the way in and then clock wise and then counter clock wise 1.5 turns? Thanks for you help so far!
It should come out to between 1.5 - 2.5 turns out. Here's the detailed procedure. The page is for the 250F, but it's the same deal for the big bike.

http://www.thumperfaq.com/jetting.htm#PJ

If the slip fit is loose, and you suspect that it's leaking, apply a bit of high temp silicon RTV sealer to the joint, assemble it and remove any excess. Give it a good 12 hours to set up. The RTV will actually burn, but it will remain in the joint and stop the major part of the leak.

Also, the main jet has nothing to do with decel popping. Some popping is normal for YZF's, and if it never does it, it's too rich. Loud or continuous exhaust backfire throughout deceleration is excessive, and is a symptom of a lean pilot circuit or an exhaust leak.

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It should come out to between 1.5 - 2.5 turns out. Here's the detailed procedure. The page is for the 250F, but it's the same deal for the big bike.

http://www.thumperfaq.com/jetting.htm#PJ

If the slip fit is loose, and you suspect that it's leaking, apply a bit of high temp silicon RTV sealer to the joint, assemble it and remove any excess. Give it a good 12 hours to set up. The RTV will actually burn, but it will remain in the joint and stop the major part of the leak.

Also, the main jet has nothing to do with decel popping. Some popping is normal for YZF's, and if it never does it, it's too rich. Loud or continuous exhaust backfire throughout deceleration is excessive, and is a symptom of a lean pilot circuit or an exhaust leak.

Thanks for the link. The slip fit is not loose at all, so that's probably not where the popping is coming from. Thanks for the info of the main jet. My problem is probably the lean pilot circuit (is that the same as a jet?). How hard is it to change the jets? Thanks again, Steve.

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Try the adjustment procedure first.

The pilot jet is an element of the pilot circuit.

Changing the main jet is pretty simple, and can be done without removing the carb, or even the entire float bowl. The pilot can also be changed this way, but you will most likely need to rotate the carb a little to get a screwdriver up into the jet (advisable to remove the hot start cable so as not to break the plastic nut), and care must be taken in selecting a screw driver the fits the jet as completely and optimally as possible, so as to avoid stripping out the slots.

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