What jets? (Modded WR450)

Thinking I need to make sure my bike has the right jets and then get it dyno tuned.

It's a UK 03 WR450 Supermoto, YZ exhaust cam, YZ tensioner, full Akrapovic. It was jetted by feel when the camshaft was fitted but I'd like to know for sure that's it's set up properly as it isn't much quicker than my brothers stock WR450 ’04 :-(


1. What size jets should I have? Is there a decent jet kit I can give to whoever dyno tunes the bike?

2. How can I tell what jet I have fitted currently?

3.Anyone know any good carb dyno tuners in SW UK?

4. I have an old style Akrapovic system which is really loud, want to do more track days next year so looking for a new exhaust that has the option to run with a 94db insert and also with out it, can anyone recommend one that's not too expensive? Was looking at DEP S7, any good?

Tear into the carb and look at the numbers on the jets. This will tell you what jets you have in the carb. Then at the top of this forum, in the "stickies", is a jetting section. You need to look this over and see what jets you should be running.

Thanks, will try to have a look. Also the stickie does not deal with a modded WR. I can't be the only one with this bike with these mods, just looking for a little guidance.

No problem. And there is a ton of guidance on jetting the modded WR correctly. Do a search, and you will find everything you need.

Thanks again, I keep reading about a JD jetting kit but I cannot get this in the UK.

JD jet kits are always the way I went, but seeing as how you can't get them, there not needed anyway. You can achieve the same thing (some say better) by ordering up jets/needles from Yamaha, etc..

We will help, but you've got to do the work too. First things first, you've got to let us know what jets your running, and then, we can help.

Ok that's cool. The bike is in winter storage but I will get to it and have a look. So to get me started, what's the easiest way to get at the jets, do I need to take the carb off the bike completely?

Use your Yamaha manual, and it will help you. And yes, removing the carb will probably be the easiest way.

Ok thanks.

Use the NCVS needle instead of the JD needle for a better transition.

Also, if you upgrade the accelerator pump linkage spring (merge) the pump will work in better conjunction with the throttle.

I use the NFLR needle from a yz 450 f middle clip with good resuilts at 5000 ft

Make sure you are running a 165 or bigger main jet .

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