AIS, and exhaust mod questions

Hello all,

Great site. I am new to bikes so I will be reading a lot.

I have been reading for days and I am still a little confused. I have a few dumb questions.

I got a 06 WR450f about a week ago. Got the AIS mod pack from Yamaha, first mistake. I did the AIS, Grey wire, and Air box. The AIS plugs they give you dont have a clean look and fit loose. I will be ordering the pretty plug kit from here to take care of that. Also an adjustable fuel mixture screw.

Yamahas kit p/n GTY-5T J93-69-00 for the 06 comes with a 48 Pilot jet and a jet needle and clip that gets clipped on the needle at space 4, thats it.

It said to install the jet needle then adjust the fuel mixture screw 2 turns out. I did it in the wrong order now that I look back.

Anyway the questions.

1) Will this cause a problem doing it in the wrong order?

2) Should I order and replace any other jets if i am not worried about treeling every inch of power?

3) While trying to do the exhaust mod I found two 1/4 inch or so holes drilled in the side of the tip. Looks like the rivets were drilled out. It had a hose clamp covering the holes. I took the tube off down to the spark arrester and dont see where the baffle is that needs removed. Maybe this mod had been done because the throttle stop screw was cut off also already.

Just looking for confirmation of this.

Mine has this outer tube but not the inner like this pic has. Guessing the inner is the baffle.

But this one looks like the whole tube comes off

I am a little confused on this. Does the outer tube stay full length?

I am sure the answers to my questions are on the board somewhere but after hours and hours of looking and reading my eyes are too sore to keep looking.

Thanks guys


The order is not ket, but the setting they tell you to do is a starting point. You should furtheer fine tune the fuel screw thusly:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Outter tube stays put. Your bike may never of had the inner or it was already removed.

The order shouldn't matter, as long as you do all the mods. You might want to consider looking at what main jet size the carb has, then get a couple of other main jets. Look under the WR450 jetting thread to find someone who rides at similar altitude/temperature to get an idea of what jetting specs to use. Sounds like the exhaust plug was already removed. Is the current tube about 5/8" wide? If it is, then it's probably been done. The removed rivet holes also indicate that's the case. Most people leave the tube at full length. What I did was remove the entire baffle and leave the spark arrestor in place, the muffler breathed better and was still quiet.

Thanks guys.:p

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