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Air/fuel mixture problem...

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Old 10-25-2010, 08:50 PM
xtremess xtremess is offline
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Default Air/fuel mixture problem...

Quick summary of bike... 2001 sportster 883, SE intake, SE II pipes, and has been jetted....

can anyone give me a idea of how many turns out the air/fuel mixture screw should be, at least a ballpark area, bike has been running to rich, plugs are complety covered in soft black soot... right now the screw is 2 3/4 turn out... i tried following some "reset your idle and air/fuel mixture on CV carb" threads and is not working, i have no tach so setting the rpm is difficult and just by ear, im more concerned with getting the air/fuel mixture right...

the cap was already removed when i got the bike, from my understanding with it being jetted there would be no reason to mess with the air/fuel screw... bike runs ok, could be better, just want it to run normal like its supost to... i have some coughing through the intake while cruising and poping at idle when giving it a little gas...

if someone could give me a easyer way to set the idle and air/fule mixture or has the same set up and can tell me where there screw is set... anythign will help thanks...

Last edited by xtremess; 10-25-2010 at 09:47 PM.
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Old 10-25-2010, 09:14 PM
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cHarley cHarley is offline
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2.5 turns out is the "typical" starting point, but you adjust from there based on rpm change. That said, there is no such thing as "Stage 1 jets". Jets come in different sizes and you need to find out which ones were installed in your carb.
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Old 10-25-2010, 09:37 PM
xtremess xtremess is offline
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Originally Posted by cHarley View Post
2.5 turns out is the "typical" starting point, but you adjust from there based on rpm change. That said, there is no such thing as "Stage 1 jets". Jets come in different sizes and you need to find out which ones were installed in your carb.
no idea what are in it, only reason i refer'd to them as stage 1 jets is thats what i was told, i am very new to harley and carbs, ive only owned newer street bikes which were all FI...

all i know is it was jetted when the pipes and intake were installed... i may try and back it down slowly here and there and see how it runs...
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Old 10-26-2010, 06:56 AM
Spur56 Spur56 is offline
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Go to the CV Performance website, they have a lot of info on tuning a CV carb. It is not that hard, just takes some time and patience. May need to decrease the size of your pilot jet, but make sure you get the mixture screw right first.
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Old 10-26-2010, 12:19 PM
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This is a very good detailed article on carb tuning. Including pictures.
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Old 10-26-2010, 01:16 PM
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So many people just slap in a bigger jet or buy the kit and then install the biggest one in there (big jet= more power, right?? ) and call it "jetted". I had to make several adjustments to mine after buying it because even though it had been "jetted" it wasn't right. It takes time and patience to get it right. It's not a difficult process but you definately need to understand how the different fuel circuits work, how to adjust them, and what effect adjusting them will have if you want to get it "right". I highly recommend reading up on all of the info you can to try and understand what's going on in that little fuel mixer.

Here's a crash course but keep in mind this is a VERY simplfied version:
There are 3 basic circuits you need to deal with

-the pilot circuit: this controls the mix at small throttle openings, such as idle, cruise and even gentle take-offs.

-the needle and needle jet: this will control the mix at middle throttle openings (like 25-75%) such as med to hard accerating or even passing/ going up a steep grade.

-the main jet: this will control the fuel mix from like 75% to wide open.

I've had best success w/ tuning "from the top down". Each circuit affects the one below it; ex. the main jet does affect the low-mid throttle mix but to less of a degree than the wide open mix. There is "overlap" between circuits. Get the main jet right first, then the needle, then worry about the pilot jet or pilot screw settings.

One trick to tuning is to find a wide open back road somewhere and make some runs (please don't do this in town or around people/traffic).

Crack the throttle wide open and leave it there for several seconds (I find 3rd or 4th gear to be best as the lower gears rev out too quickly). After you've held it open for a few quickly roll off the throttle slightly: keeping it open to like 90%. If your main is too big the bike will make a slight stutter, if it's too lean it will surge forward slightly. It may take a few runs before you get a good feel for it and the longer you hold it open the stronger the feel will be (stay off of the rev limiter though).

Same thing for the needle setting. Get the bike going in 4th or maybe 5th and roll on the throttle to maybe 3/4 open. Hold for several seconds and then roll off slightly. Same thing as the 1st: stutter and it's too rich (lower the needle), surge and it's too lean (raise the needle). It's not until you start doing some MAJOR mods that you really need to worry about changing the actual needle jet- adjusting the needle heigth is normally enough.

The pilot is best adjusted using the "idle drop" method described on this forum. I've found for this to work though the idle speed has to be VERY low, almost to the point of dying. Listen carefully and you'll hear the idle speed drop or the bike start running rougher as you turn it in and then again as you keep turning it out. If you have to go more than about 3.5 turns out (from LIGHTLY seated) on the pilot screw you should go up 1 pilot jet size and try again. After that take it for a spin and adjust the pilot setting so that it runs smooth at small throttle openings, cruises nice w/o surging or loading up and it transitions smoothly to the needle jet as you roll on it. This setting tends to be the most forgiving of errors but you must get the others tuned right first or you'll end up chasing your tail w/ a bike that's rich up or and fine in the middle, or lean on top but fat in the middle or some other problem.

Like I said, this is the simplified version but if you do this you should get pretty close. Also, keep in mind, one guys settings may not work on another guys bike elsewhere. Altitude, temp, and other things can have a very big affect on jetting.

If you really wanto to get into it drilling the slide lift hole does help the mid-upper transition quite a bit but I'll save that for later.
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