Mixture Screw Setting on Stock Carb
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Tourer
Joined: May 2011
Posts: 469
Likes: 158
From: Alberta
Mixture Screw Setting on Stock Carb
I've looked on many forums and sites to try and find the answer - what is the stock mixture screw setting on an unmolested HD evo carb, before the plug is removed. In other words what does the factory set the mixture screw on these bikes when they roll off the assembly line bone stock. This would be for a late model evo as the earlier ones may have had slightly different jetting.
In my searching I've only found one reference, and that was it was set at 1/2 turn out. I would like somebody to confirm that if possible. There is no end of information on richer jetting but I'm just looking for information on stock bikes/stock jetting. One always needs a baseline from where to start. Thanks for any info.
In my searching I've only found one reference, and that was it was set at 1/2 turn out. I would like somebody to confirm that if possible. There is no end of information on richer jetting but I'm just looking for information on stock bikes/stock jetting. One always needs a baseline from where to start. Thanks for any info.
Seasoned HDF Member
Joined: Aug 2006
Posts: 24,492
Likes: 30,780
From: Pennsylvania
Do not know the factory setting; however, here is information that may assist, for a Sportster but should be the same for any CV carb.
Thus far, the throttle plate has been positioned (as much as possible) between the Idle Port & the Transfer Ports, the Slow Jet has been chosen as stock or a 45 if the engine is 1200 or Stage One, the IMS cap was removed and the IMS was adjusted to 2-1/2 turns out from GENTLY seated. In addition, a selected needle was installed in the slide along with a reasonable choice for the Main Jet. These parts and settings were selected to provide a valid STARTING POINT for further, more accurate, adjustments.
While the proper idle rpm will be set AFTER adjusting the IMS setting (using the Idle Speed Screw), it is important to isolate the Idle Port operation from the Transfer Ports.
http://sportsterpedia.com/doku.php/techtalk:evo:carb02
Thus far, the throttle plate has been positioned (as much as possible) between the Idle Port & the Transfer Ports, the Slow Jet has been chosen as stock or a 45 if the engine is 1200 or Stage One, the IMS cap was removed and the IMS was adjusted to 2-1/2 turns out from GENTLY seated. In addition, a selected needle was installed in the slide along with a reasonable choice for the Main Jet. These parts and settings were selected to provide a valid STARTING POINT for further, more accurate, adjustments.
While the proper idle rpm will be set AFTER adjusting the IMS setting (using the Idle Speed Screw), it is important to isolate the Idle Port operation from the Transfer Ports.
http://sportsterpedia.com/doku.php/techtalk:evo:carb02
Road Warrior
Joined: Dec 2012
Posts: 1,539
Likes: 692
From: magnolia tx
Range is 2-3 turns out, less than two turns and the bike runs smooth, step down intermediate jet size, more than three turns out and bike runs smooth bump up the size intermediate jet
Last edited by mike131; Jul 28, 2022 at 11:15 AM.
HDF Community Team
Joined: Dec 2005
Posts: 5,402
Likes: 2,605
From: NC USA
Finding one with the plug still intact is rare, especially these days. I've drilled the plug out of 3 thru the years. They were each within a tick either way of 1-1/8 off the seat.
Thing is, you can simply rebuild the original carb off an all original bike and chances are it won't tune out at the same turns on the screw when you put it back on. Point being, don't worry about the mixture screw position, do what works for what you have. With exception of changing the air cleaner, any changes to the bike are going to affect where the mix screw needs to be - that includes miles of operation as well. Things wear, break-in, wear out. Anything other than a factory fresh CV40 on a factory fresh engine will seldom operate properly without some bit of adjustment.
Thing is, you can simply rebuild the original carb off an all original bike and chances are it won't tune out at the same turns on the screw when you put it back on. Point being, don't worry about the mixture screw position, do what works for what you have. With exception of changing the air cleaner, any changes to the bike are going to affect where the mix screw needs to be - that includes miles of operation as well. Things wear, break-in, wear out. Anything other than a factory fresh CV40 on a factory fresh engine will seldom operate properly without some bit of adjustment.
Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
Likes: 3,357
From: Cental, MI
Finding one with the plug still intact is rare, especially these days. I've drilled the plug out of 3 thru the years. They were each within a tick either way of 1-1/8 off the seat.
Thing is, you can simply rebuild the original carb off an all original bike and chances are it won't tune out at the same turns on the screw when you put it back on. Point being, don't worry about the mixture screw position, do what works for what you have. With exception of changing the air cleaner, any changes to the bike are going to affect where the mix screw needs to be - that includes miles of operation as well. Things wear, break-in, wear out. Anything other than a factory fresh CV40 on a factory fresh engine will seldom operate properly without some bit of adjustment.
Thing is, you can simply rebuild the original carb off an all original bike and chances are it won't tune out at the same turns on the screw when you put it back on. Point being, don't worry about the mixture screw position, do what works for what you have. With exception of changing the air cleaner, any changes to the bike are going to affect where the mix screw needs to be - that includes miles of operation as well. Things wear, break-in, wear out. Anything other than a factory fresh CV40 on a factory fresh engine will seldom operate properly without some bit of adjustment.
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Seasoned HDF Member
Joined: Jul 2014
Posts: 8,590
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From: Cental, MI
Seems like you would be closer to 1 than 2 with larger Intermediate... I will check mine....Soon!!!!