Proper Fuel Screw Adjustment???

I'm new to Team Blue, so forgive me. What is the proper way to adjust the fuel screw? I am coming from a late model XR600 that was just a kick and ride deal every time, but I am lost when it comes to constantly making adjustments like this.

I have a stock 01 426 with Yosh pipe, Uni air filter, Boysen pump cover, and a Zip Ty fuel screw adjuster. So far, I have been trying to get the jetting dialed in, but it has a bog sometimes down low, a flat spot at 1/2 throttle, and absolutely RIPS up top.

So back to the original question, what is the proper method to adjusting the fuel screw??

Thanks in advance. :applause:

turn it in to lean, turn out to richen. recommended starting point is 1&1/4 out.

I sent you a private message, since the write up is so long. I usually have my fuel screw set so that I get a Little popping on de-celleration. You don't want popping all the time, but a little pop when closing the throttle, seems to give the crispest response.

Flint Lock could you send it to me as well?

flintlock28 -

THANKS FOR THE INFO!!! HUGE HELP!! :applause:

I wouldn't mind receiving that myself if you don't mind. Thank you...

I sent you a private message, since the write up is so long. I usually have my fuel screw set so that I get a Little popping on de-celleration. You don't want popping all the time, but a little pop when closing the throttle, seems to give the crispest response.

teamster, private message me your regular e-mail address. Thumpertalk has a limit to the number of words per message, and it won't fit.

Don

flintlock 28 - I hope this is OK, but I copied and pasted your message so everyone can see.

You the MAN!! :applause:

QUESTION 11: HOW DO I ADJUST THE FUEL SCREW?

Not so fast. Before you ever touch the fuel mixture screw, you must first warm the engine up. That means riding the bike around a bit, not just starting it up. Once the bike is warm, you need to bring it up to a fast idle.

QUESTION 12: HOW FAST IS A FAST IDLE?

How fast is a fast idle? As a rule of thumb, it is about 1800 rpm. The best way to get a fast idle and keep it is with the idle adjustment screw.

Some race mechanics simply crack the throttle by hand and hold it there. This is common, but it's much more accurate to set the fast idle with the slide stop.

QUESTION 13: WHAT IS THE NEXT STEP?

With the bike holding a steady, high idle, use the adjustment tool to slowly screw the fuel mixture screw in. Continue tightening the screw until the engine rpm drops (and nearly dies). Now, slowly turn the screw back out. You will hear the engine rpm begin to speed up and the exhaust note will become crisper.

QUESTION 14: WHEN DO I STOP TURNING THE SCREW OUT?

Stop turning the fuel mixture screw at the exact moment when the engine hits peak rpm. Peak rpm is when the engine runs the cleanest and fastest. When you reach that point, the idle won't become faster the more you turn the fuel mixture screw out. If you keep turning the screw, the rpm will stay up but the exhaust note will become dull, flat and lumpy.

QUESTION 15: WHAT'S A FLAT. DULL AND LUMPY EXHAUST NOTE?

It's not defined by speed but rather by crispness. When engine rpm just peaks, the exhaust note is sharp and crisp. As you continue to turn the fuel mixture screw, the exhaust note will become choked by too much fuel and will lose that snappy sound.

QUESTION 16: BUT WHEN DO I KNOW TO STOP?

Once you've trained your ear to hear what peak rpm sounds like� and have a good idea of the point where turning the screw out farther hurts performance�you might test your setting by turning the fuel screw in the opposite direction (until the rpm drops). Stop at that instant and turn it back in again. If you're not 100 percent certain you have peak idle, start counting the turns out from the spot you think is peak idle. If the engine rpm doesn't pick up after a 1/4 twist, turn it back to the original spot.

QUESTION 17: HOW DO I TELL WHAT MY SETTING IS?

Count the turns. With the engine off, turn the fuel mixture screw in while carefully counting in l/8th turn increments. Keep counting until the screw lightly bottoms. Now, turn it out the identical number of l/8th turns. That is your fuel mixture adjustment and it's usually between 1/2 to two turns out.

QUESTION 18: WHAT IF I HIT PEAK RPM AT THREE TURNS?

As you turn the fuel mixture screw out, the slow speed mixture circuit is metering more and more fuel to the engine. If the engine doesn't reach peak rpm until the screw has been turned more than two turns, it might indicate that the pilot jet is too small (lean). Try the next larger pilot and retest the fuel mixture adjustment. Conversely, if peak rpm is reached before you turn the fuel mixture screw out a half turn, it could mean that the pilot jet is too rich. Try the next smaller size.

QUESTION 19: IS THE PILOT JET THE BEST FIX?

No. Even if the fuel mixture screw is set at 2-1/2 turns out, the bike might not run as well with the next size richer pilot. But you still need to try it in order to rule it out. Always try a respective leaner or richer pilot if the fuel mixture screw's best setting is on either side of the one-half or two and one-half turn adjustment range. Pay atten�tion to how the bike runs at the crack of the throttle. Switch back and forth if necessary. Do not rule out the needle clip position or nee�dle taper. All can affect off-throttle performance�even with the cor�rect fuel mixture screw setting.

QUESTION 20: HOW OFTEN SHOULD THE FUEL SCREW BE CHECKED?

Every race day. Twice a day if it is cool and overcast during practice and bright and sunny for the first moto. When the track dries out and the sun breaks out, you'll want to set the mixture screw back to a leaner setting.

QUESTION 21: WHAT CHANGES NECESSITATE FUEL SCREW ADJUSTMENT?

Temperature isn't the only thing that affects the fuel screw. When racing in elevations above 4000 feet, the thin air will create the need for more air (turn the fuel mixture screw in). In humid climes, you might need to lean the setting in the afternoon as the day dries out. A fast approaching storm will require a richer setting (turn the fuel mixture screw out).

:D:prof::prof::bonk::lol::p:applause::ride::eek::eek::eek::eek::prof: :prof: :prof::prof::prof::prof::prof::naughty::naughty::naughty::naughty::naughty::naughty::naughty: :naughty: :naughty::naughty::naughty::naughty::naughty::naughty::naughty::naughty::naughty::naughty::naughty:

Good post.

good post

It's a reprint from MXA

There is also this:

http://www.thumperfaq.com/jetting.htm#PJ

On a 450, the only difference is that the max turns out before going to a larger pilot should be closer to 2 1/2.

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