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What is this for?

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09 wr250f  there is a red know under the carb with sides labeled 1 thru 4. What is it?

20180213_175510.jpg

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12 minutes ago, ehall said:

09 wr250f  there is a red know under the carb with sides labeled 1 thru 4. What is it?

20180213_175510.jpg

Remember to check it VERY OFTEN, some have a tendency  to back themselves out. Go ahead and ask me how I know.

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micro tuning adjust of the idle circuit. When tuned right, it is usually about 1.5 turns out from bottom. It has the potential to guide you to the proper idle jet if the best idle is outside of the normal parameters.

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Yes, that is an aftermarket fuel screw.  The stock screw sits up in the hole and you have to have a really small screwdriver to adjust it.

By rule of thumb, once you get the bike running at it's happy spot (on the bottom end) count the number of turns out from the screw all the way in.  A full turn of the screw is equal to approximately 1 size on the pilot jet.

For example, if the screw is only out 1 full turn, you could theoretically install a one size smaller pilot jet (if you have a 45, try a 42) set the screw to 2 turns out, and it should be close to the same.

Typically, I only adjust the fuel screw once I have my baseline setting when I am having large changes in altitude.  I like to run around 2 turns out for my base altitude (3700 ft) so that when I venture lower I have a little room to get more fuel (up to 3 turns) or go up higher in the mountains (1 turn out from full in).

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It’s your fuel mixture screw on your idle circuit. Stock, there was a screw that you had to us a tiny and short screw driver to make your adjustments. This is obviously aftermarket, but makes life MUCH easier. Check your service manual for the stock starting setting, then adjust from there. If you have a Boyesen quick shot, the setting to start from is two turns out, then adjust from there. Once it runs nicely, you may have to adjuste your idle knob to where you like the idle speed.

Im always screwing with mine, because I live at altitude where it needs to be a little rich, and race at near sea level where it needs to be leaned out. 

Good luck with it 👍

Edited by Dirt Hog

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Could be part of something like a JD jetting kit https://www.jdjetting.com They sell kits specific to your bike, which are developed and dyno tested to maintain best specs. If your bike runs and idles well, it is probably set up already. The advice given above is good if you like to tinker. Lot's to learn in setting-up carbs. Cheers! 

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Fuel screw hell...don't let them fool you that is the turbo boost dial.  Some use it to complement their NOS system.  It comes in pretty handy at the track.  Can't quite clear the triple...turn it up to 4.  

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14 hours ago, N-8 Dawg said:

Fuel screw hell...don't let them fool you that is the turbo boost dial.  Some use it to complement their NOS system.  It comes in pretty handy at the track.  Can't quite clear the triple...turn it up to 4.  

Of course the first thing you do is turn it up all the way! Flux capacitor control knob.  Lol. Bike runs great so no tinkering yet.

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18 hours ago, Dirt Hog said:

It’s your fuel mixture screw on your idle circuit. Stock, there was a screw that you had to us a tiny and short screw driver to make your adjustments. This is obviously aftermarket, but makes life MUCH easier. Check your service manual for the stock starting setting, then adjust from there. If you have a Boyesen quick shot, the setting to start from is two turns out, then adjust from there. Once it runs nicely, you may have to adjuste your idle knob to where you like the idle speed.

Im always screwing with mine, because I live at altitude where it needs to be a little rich, and race at near sea level where it needs to be leaned out. 

Good luck with it 👍

How much elevation are you able to adjust for without changing the pilot jet?

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On 2/15/2018 at 9:57 AM, ehall said:

How much elevation are you able to adjust for without changing the pilot jet?

I go from about 4800’ at home to approximately 900’ and change at the track. It runs ok at home, but I’m usually only test riding it after repairs or practicing hole shots. It runs great at the track. So I honestly can’t answer that one.

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On 2/14/2018 at 7:23 PM, N-8 Dawg said:

Fuel screw hell...don't let them fool you that is the turbo boost dial.  Some use it to complement their NOS system.  It comes in pretty handy at the track.  Can't quite clear the triple...turn it up to 4.  

Mine goes to 11. 

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41 minutes ago, Dirt Hog said:

Mine goes to 11. 

Mine did too. 20 years ago. Lol. Sucks getting old. Now I can only choose 1-4. 

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