mods on an 03 wr450f searching for the fuel mixture screw

10 replies to this topic
  • just an old biker

Posted July 09, 2008 - 05:20 PM


Hello everyone, I just recently joined TT. I have thoroughly enjoyed and have found very useful all of the information. My husband usually does all of the work on my bike, but I wanted to learn a little about doing some of the mods myself to liven up the bike.:p :thumbsup:

I have been searching for a picture of where the fuel mixture screw might be located
I could use some help. I've ridden bikes for many years, but I just got a 03 wr450f. I wanted to do some mods. So far I've just removed the grey wire, and the baffle in the exhaust.
I thought I'd replace the fuel mixutre screw, but which one is it?

Also, is it true that if you turn the choke button you increase or decrease the throttle?
any help would be appreciated.
just an old biker

  • bigwhoppa

Posted July 09, 2008 - 07:43 PM


here is a link with a pic of where the fuelscrew is located. It is hidden up the hole at the front of the carby. http://www.thumperfa.../fuel_screw.htm

The choke knob is purely a plunger. You may be getting confused with the idle speed adjustment screw knob which is next to the choke.

  • Desracer

Posted July 09, 2008 - 09:48 PM


Do a search here on TT and you will find photos and how to do all of the mods. You will have to buy a new aftermarket fuel screw for ease of use, which is also is the TT store for a good price.

  • William1

Posted July 10, 2008 - 02:26 AM


Stock fuel screw is tough to remove with the carb on the bike without special tools. It is located on the bottom of the carb, on the engine side of the front of the float bowl. Put a small mirror under the carb, you'll see a 1/4" hole with a brass scww way up inside.

Here are the instructions from Merge Racing on how to do it:

And no, rotating the choke know has no effect. The 'choke' (really an enricher) is merely a plunger type of valve, open or closed.

  • just an old biker

Posted July 11, 2008 - 04:28 AM


Well , it looks a bit more complicated than I thought it would be.

There is one problem that has occurred since I removed the grey wire, and removed the exhaust baffel.
The engine refuses to keep running unless the choke is pulled out.
I imagine, that this is because it needs more gas so unless I complete the rest of the mods, the bike isn't going to run like I want it to.

The bike has been jetted for 5000 ft. but I'm running it in Florida. But in the future it will be running up to 9000ft. could this have an effect on performance right now?
If so, what would be my solution?

I appreciate your comments

Just an old biker

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  • William1

Posted July 11, 2008 - 07:38 AM


If the bike fails to idle, you will need to visit the idle adjustments. This consists of the dreaded fuel screw, pilot jet (inside the float bowl, under the large cap, needs a tiny screw driver or special tool to remove the jet) and the idle speed knob.

Typically, elevation changes greater than 2,000' call for jetting changes. Pilot/fuel screw (they work together) needle, clip position and main jet. In some instances, leak jet too.

  • just an old biker

Posted July 22, 2008 - 04:57 AM


:thumbsup: I found the fuel adjustment screw:applause:
There are a couple of videos on Youtube that showed me how to change out the fuel screw , also do the air box mod. I adjusted the fuel mixture to be a little richer and now I can run the bike without the choke being on:applause: :thumbsup: . I hope this doesn't foul the plugs.
Now I'm going back and unplug the gray wire andI'll see what happens then.

  • William1

Posted July 22, 2008 - 05:04 AM


Double check that the hot start cable is connected properly to the carb.

  • just an old biker

Posted July 23, 2008 - 04:03 AM


what does the hot start cable do?

  • just an old biker

Posted July 23, 2008 - 04:13 AM


Another thing I discovered when I finally found the fuel screw was, the previous owner had already replaced the factory one with an adjustable screw. The screw was adjusted to about a half turn out I adjusted it to about 5 turns out, now the bike starts on the first or second attempt with the choke on, and after it warms up , take the choke off, it will keep running. I also adjusted the engine idle. that raised the idle enough so that it doesn't cut off. Still haven't removed the grey wire. I'll check where the hot starter is located.

  • WR_Dave

Posted July 23, 2008 - 04:49 AM


If you've turned the fuel screw out 5 full turns, you are in danger of it falling out while riding. You will need to go 1 or 2 pilot jet sizes larger to get the fuel screw back into the 1/2 -2 1/2 turns range. Remember what was in there to begin with so you can change it back for the 9000 ft you mentioned. The Hot start allows air to bypass the carb and help the engine fire up when it is hot or flooded. If the hot start isn't adjusted correctly then you may be compensating for extra air getting in, by giving the engine more fuel than it really needs. Keep working on it and track your changes so you start to learn what each change does. Also download the service manual here.

Good Luck - WR Dave


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