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Discussion Starter · #1 ·
Popping and backfiring on deceleration would mean I'm currently running lean, correct?

I'm adding a new exhuast soon (currently stock). Will this make it run even leaner?
 
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Discussion Starter · #2 ·
you may need to raise the needle or up the pilot jet. what bike is it? i wouldn't do poop if you're about to put a new exhaust on.
 
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Discussion Starter · #3 ·
Re: (Nick Novice)

'02 WR250F

I'm not going to adjust anything until the pipe is on. Just looking for someone to point me in the right direction or let me know what I should expect.

According to FedEx, the new pipe is on my doorstep right now.
 
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Discussion Starter · #5 ·
Re: (Nick Novice)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nick Novice »</TD></TR><TR><TD CLASS="quote">you may need to raise the needle or up the pilot jet. </TD></TR></TABLE>

Wrong-o. On deceleration, the throttle is closed, the needle and the main jet have almost nothing to do with fuel delivery.

Dave needs to a) make sure his exhaust system is not leaking at the header or anywhere else

and if not,

b) open up his fuel screw ( as long as he doesn't go more than about four turns out)

If the fuel screw is already wide open, Dave needs to go to a larger pilot jet and reset his fuel screw accordingly.

Really cold air is dense and can cause a lean condition... I bet Dave's just a turn of the fuel screw from fixing his popping.

His new pipe may or may not have an effect on the idle circuit... it depends on how restrictive the stock exhaust was.
 
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Discussion Starter · #6 ·
Re: (Dave)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dave »</TD></TR><TR><TD CLASS="quote">I'm not going to adjust anything until the pipe is on.</TD></TR></TABLE>

It's just a fuel screw. Do it.

While you're in the parts buying mood, get an externally adjustable fuel screw... they rock.
 
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Discussion Starter · #7 ·
Re: (banda)

Thanks for the tips Bill, I'll do as you suggest as soon as we get a nice day around here.

The popping and backfiring was occuring at the last track day we did back in November. It was around 70 degrees and dry (perfect), and I had recently installed a different air filter set-up for better breathing.

Although the exhuast is stock, I did have a PMB insert that is supposed to allow better flow.
 
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Discussion Starter · #8 ·
banda, you are so right on the fuel screw. i stand corrected. the needle doesn't come into play until you crack(not whack) the throttle.

i'm 0 for 2 on the banda count. unlike last time, i read the complete post before posting a reply and still goofed it up. i need to get away from the computer. but i still have 2 hours left on the clock. dave, you haven't changed anything with the airbox have you? did you buy one of the billet fuel screws? i found that they need low strength loctitie on the threads as the tension from the spring wouldn't hold mine in well enough. just a thought.
 
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Discussion Starter · #9 ·
Re: (Dave)

Here's the short version of how to set the fuel screw:

Start the bike with the fuel screw two turns out from fully closed.

With the machine idling and warm, bring the idle up with the idle adjuster screw so it's idling fast. Not racing, but a fast idle.


Turn the fuel screw in until the idle starts to drop.

Turn the fuel screw out, counting the number of quarter turns, the idle will come back up, keep turning it out and counting until the idle starts to drop again.

Once the idle has started to drop, back the screw back in half the number of quarter turns you counted. You're done. Set your idle back to where it should be and go ride.

If the idle doesn't drop when you turn it in, your pilot jet is too big. If the idle doesn't drop by the time you've turned the screw out four and a half full turns from fully in, your pilot jet is too small. Install a different size pilot jet and start over.

The externally adjustable fuel screws are cool because you can turn them by hand, and they have big numbers on them so it's easy to count the quarter turns.
 
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Discussion Starter · #10 ·
Re: (banda)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by banda »</TD></TR><TR><TD CLASS="quote">Here's the short version of how to set the fuel screw:

Start the bike with the fuel screw two turns out from fully closed.

With the machine idling and warm, bring the idle up with the idle adjuster screw so it's idling fast. Not racing, but a fast idle.


Turn the fuel screw in until the idle starts to drop.

Turn the fuel screw out, counting the number of quarter turns, the idle will come back up, keep turning it out and counting until the idle starts to drop again.

Once the idle has started to drop, back the screw back in half the number of quarter turns you counted. You're done. Set your idle back to where it should be and go ride.

If the idle doesn't drop when you turn it in, your pilot jet is too big. If the idle doesn't drop by the time you've turned the screw out four and a half full turns from fully in, your pilot jet is too small. Install a different size pilot jet and start over.

The externally adjustable fuel screws are cool because you can turn them by hand, and they have big numbers on them so it's easy to count the quarter turns.</TD></TR></TABLE>

Thanks Bill!
 
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Discussion Starter · #11 ·
Re: (Nick Novice)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nick Novice »</TD></TR><TR><TD CLASS="quote">did you buy one of the billet fuel screws? i found that they need low strength loctitie on the threads as the tension from the spring wouldn't hold mine in well enough. just a thought.</TD></TR></TABLE>

The billet screws are heavy, and the spring does a pitiful job of keeping them in if they are turned out excessively. If you use a larger pilot jet, you can turn the fuel screw in further where the spring can hold it better.
 
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Discussion Starter · #12 ·
regarding the fuel screw, I got the Storm Cycles one, the pic doesn't show it, but they've added another groove with an o-ring in it about 3/8" above the "knob" part, which keeps the screw from backing/falling out of the carb (I've kept an eye on mine & had no problems). If I were gonna buy one now though, I'd probably get the KoubaLink one instead though, as it's made of brass, & isn't as soft as the aluminum ones (there are rumors of guys breaking the tips off the alu. ones when "seating" them).

 
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Discussion Starter · #13 ·
I Didn't see what bike you have in your post it looks like a Yamaha in your Avatar.

Up the pilot 1 if it persists up it 2 and a 1 or 2 size richer main jet is recommended for supermoto. Lean will kill your horse power and is not good for the engine, the pilot will correct your problem.
Theirs so much deceleration in supermoto you need the richer pilot to make sure your not going to damage your engine. Use the screw to fine tune between tracks and temperature changes.

I haven't noticed any different jetting among different brands of pipes.
 
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Discussion Starter · #15 ·
Re: (Dave)

Bob's has the Zip-Ty fuel screws hanging on the wall right by the cash register.
 
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Discussion Starter · #16 ·
Re: (Latebraker)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Latebraker »</TD></TR><TR><TD CLASS="quote">Bob's has the Zip-Ty fuel screws hanging on the wall right by the cash register.
</TD></TR></TABLE>

I have a Bob's gift certificate tucked in the visor of my car, perfect!
 
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Discussion Starter · #18 ·
Re: (banda)

Sorry, but is there a dial 'a' jet available for bikes?
I've had a pair on a snowmobile before. Adjust for altitude and temp in seconds, worked great!
 
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Discussion Starter · #19 ·
Re: (Stookes24)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Stookes24 »</TD></TR><TR><TD CLASS="quote">Dave where have u been riding?</TD></TR></TABLE>

In my dreams man.

I haven't been riding, just getting ready for the upcoming season. This is just one of those issues that I never fixed at the end of last season.
 
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