'08 WR450F AIS Removal

In September 2011 I picked up an immaculate unmolested 08 WR450F. I've been riding it regularly since and am now looking to get a little more power out of it. It's a challenge to get US parts in the UK but I'm tempted to get the AIS removal kit GYT-5TJ93-69-01 shipped over.

These bikes are great to ride but a pain to work on so what I'm planning to do is remove all the AIS piping and fit the new throttle screw that comes with the pack. I've no intention of arsing around with jetting as it runs well and I need as much range as I can get from the tiny fuel tank.

I'd like to know if there is actually any performance gain from removing the AIS pipework (apart from the tiny weight loss). I've scoured the forum and it seems there's a lot of disagreement.

All the best,


No performance gain at all to removing the AIS

the original owner will have got bag with a new needle and main jet in it, with the bike, which will make it run much better, and is a must if you remove the restricted throttle stop

No need to get the AI kit from the US

Just do the following

remove the AIS and blank the hole off in cylinder head, and nipple in the inlet tract, and air box feed (or re-route the crankcase breather to this point)

Pull the snorkel off the air box

rejet to 168 main and fit the new needle with clip in 3rd or 4th groove

replace the restrcited throttle stop screw (don't run it without a screw) with a cut down oe part or the YZF screw (length details on this forum)

the grey wire mod doesn't seem to do anything on UK bikes - I can tell no difference with it dis connected.

If you worried about the small tank, get a o/size clarke tank

14L & more than big enough for a 3hr race


go ride and enjoy

Edited by GuyGraham

Thanks for that. Sadly the bag with carb bits is nowhere to be found so if I do it I'll have to source them elsewhere. I forgot to mention it is an imported US model.

I love the use of the word "just" in your list of work. It's dangerous to assume competence with this sort of thing but I'll get stuck in and see what happens. Your bike looks like it's being put to proper use but mine only gets to tool around the green lanes of Devon.




Edited by timotheus

Are u sure its a US import - Why do you think this?

Never heard of this, as WR's are imported into this country by Yamaha GB

If it is an import, the US bikes have an non-adjustable needle as std - ie it only has one groove for the circlip, so that will confim it

The code for the needle you need (the one that comes with the bike in a bag) is GDDUQ, which you should be able to get from any Yamaha dealer, or Allens Performance in Nottingham (mail order) - put it in the 4th clip from the top

#45 pilot jet (think this is std)


Other recomendations are the YZF needle (NFLR) but my Wr runds great with the GDDUQ

Check your AP squirt timing and duration (best done with a digital camera set on film mode) - instructions on this forum, in the stickies I think

If its out, you'll have a bog

Can't emphasis enough, if you de-restrict you must re-jet as they are set lean from the factory, and once you get full throttle opening, they become even leaner coz the std jetting can't cope with the fuel demand from full throttle requirments

If you get stuck, just ask on here - always help available

Have you got the Workshop Manual?

I ran the frame number by Yamaha UK and they confirmed it's a US model.

I've got the manual and will get hold of the parts and have a go.

I've got to say that in it's stock restricted trim the WR450 is the ideal machine for the Devon green lanes. We've got a combination of thick mud, slatey climbs and long straights and the bike is very responsive with torque that can cope with anything. I came from an XR250 and the WR feels lighter and much more responsive. I was wary of it to start with but now if feel right at home on it. I just need to loosen it up a little hence the original question.

Thanks for all the extra info.

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