Suggestion for Jetting??

Hey guys, I want to get my jetting correct as I am tired of it being off. I replaced one the the jets years ago, but still think I am too lean. I am not sire whats in there right now, but I will be tearing apart soon to see. Here is what I have

99 wr400 throttle stop removed, air lid removed. I also moved the needle, but did this in 99 and don't remember where.

yz timing, grey wire cut

FMF mega max II exhaust with the lowest amount of disks installed, I think its 3 or 4?

So if I could get some suggestions as to what I need to jet it at, that would be greatly appreciated. Thanks.


dyno it, though make sure its got an air/fuel trace! ideally the jetting will bring you out at 12.7:1 but a little richer i.e., 12:1 is fine, as it wont hurt anything.

the grey wire. you have disabled your rev limiter which cuts every third spark to prevent the motor going pop due to excessive revs. they put the rev limiter in the bike so as to prevent the likelihood of it detonating between your legs

Is that true. If I cut the grey wire on an 05 WR 450 then I do not have any rev. limiting? Or is that the case only for a 99.

Cutting the gray wire does NOT disable the rev limiter. Mine is cut and I have hit it on several occasions. The rev limiter does its job accordingly.

Regarding your jetting. My advice is to return the carb to stock jetting. Believe it or not, the Yamaha engineers do know what they are doing. Not trying to be an ass or anything, but I went through so much crap playing with the jetting over the years and I finally returned the carb to stock settings. Been running fine ever since. I used to have to mess with it all the time. I can't begin to count the number of fouled plugs and the number of times I have the seat and tank off to mess with the plug, jets, etc. Now that it's stock (never was before - I bought the bike used in 2000 and the jetting was all goofed up. Probably why the dude sold it.) Give it a try.

I think a lot of people are making a lot of money selling all of us WR owners fancy jet kits. They need us to believe that the jetting is messed up and all kinds of hidden power will be unleashed. My bike runs better and stronger than it ever did with what let's just call "funky" jetting.

I think the stock jetting is a great starting point, but it's just that. If it's all screwed up and not stock, I would install the stock jets and needle and proceed from there. My bike won't even start without wearing a hole in your boot and holding the throttle open with the stock pilot jet. I ended up going to a 50 pilot and a 72 starter and now she starts right every time. I live in a hot/humid climate and ride in the hills, my main and needle are both leaner than stock settings. I'm sure that my settings are going to change as we head into fall, and that's OK with me, that's why the carbs are adjustable.

Anyway, every bike is different, and most of us are riding in different areas. There are a lot of good jetting articles to be found on the net for thumpers. Most agree that stock pilot jetting is usually on the lean side for emissions purposes. The manual also has some good advice. Just try and change one thing at a time, take a test ride, note the differences and so on.

You'll get the hang of it after a while. Try to order a 48 and 50 pilot from TT, they are cheap there. Order some mains too, so you can mess around. The YZ400 comes with a 45 pilot and 165 main stock. Rip that bowl off and check to see what's in your bike first.


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