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Old 07-28-2013, 09:45 AM   #1 (permalink)
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Running lean

I have a 2003 fxdp, stock with a thunder header . I drilled out the cap on the mixture screw and went all the way in with the screw and back out the same plus a turn , should I come out more? . It still seams lean when i checked my plugs . Could I need a bigger jet? It's a 048, is this stock size and what should I bump it to ?
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Old 07-28-2013, 10:06 AM   #2 (permalink)
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I'd say so. I have an '04 FXDP that is totally stock other than a DK Customs K&N 587 AC, and that darn thing never would run on stock jets (190 main/45 slow), even before I added the DK AC. To get it to run good & not cough/pop on decel, I finally bumped it up to 195 main & 50 slow. Runs great there, & gas mileage is as good or better. Before the DK AC, I had to run a 48 slow to get it to idle & run good at light throttle. And it's not the intake gaskets leaking. Changed them twice! Made no diff.

I have no idea why FXDP's need so much jetting, but they sure seem to, in my experience anyway.
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Old 07-28-2013, 10:13 AM   #3 (permalink)
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did you do the air cleaner as well? I did a T-header on my 02 FXD as well,with an air cleaner.I used the recommended middle size jet that came in my Thunderslide kit and it's been great for almost 100,000 miles.You definitly need to go richer than stock with the main jet if you're letting more air in,that will lean it out.
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Old 07-28-2013, 10:15 AM   #4 (permalink)
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Quote:
Originally Posted by Damian View Post
It still seams lean when i checked my plugs . Could I need a bigger jet? It's a 048, is this stock size and what should I bump it to ?
Thanks
Yes, when in doubt...richen mixture first. Try the jetting mentioned from M&P340. Look for "surging" at light load cruising speeds as an indication of lean.


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Old 07-28-2013, 10:20 AM   #5 (permalink)
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How many turns out did you put on the idle needle after you removed the cap? My main indicator that I needed more slow jet was that no matter how much I turned it out, it made little or no diff to idle. That told me the slow was too small.

Wi a 50 slow, I now get best idle, and no decel pop, at 2-3/4 turns out.
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Old 07-28-2013, 11:18 AM   #6 (permalink)
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I didn't put on an air kit yet , it's got a 190/ 48 for jets. I went in all the way with the mix screw (1 and half turns ) back out the same plus a full turn. I eventually will get a big air kit but just want it to run right as set up now. Ill back it out in increment's for now and see if it makes a difference. I've never dealt with jets before so I'm kinda lost . I'm guessing I need bigger , I just don't know how much without drowning it with fuel.
Thanks for the replies
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Old 07-28-2013, 01:52 PM   #7 (permalink)
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Take your bike on a good 10 or 15 mile drive. At full warm up turn air/fuel mixture screw in untill the bike starts to stumble, then turn it out untill it stumbles (usually about a 1/2 turn difference) set it at the sweet spot in the middle and your done.

I've never had to use a 50 and have tried to understand the 48 with no avail, the 45 and 46 I've been able to get to work really well.

To understand on if you need a bigger or smaller jet depends on how many turns out the air/fuel mixture scew is. 1 or less bigger, 3 1/2 or so smaller is a good starting point.

www.nightrider.com lots of good info on carb tuning here.
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Old 07-28-2013, 02:54 PM   #8 (permalink)
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if you ever change the intake "O" ring, butter lube them in RTV.
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Old 07-30-2013, 09:31 AM   #9 (permalink)
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