Idle Question
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Cruiser
Joined: Feb 2009
Posts: 239
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From: California
Idle Question
Always wondered why when I first start my bike (98 FXST, engine stock except exhaust and air filter), why does it idle like it has a cam while cold, and then smooth out when warm?
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
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From: Near Frankenmuth, MI
I'm guessing carbed because EFI when working correctly chokes the bike precisely as needed and from my experience they do not have "cold start" issues or odd lulling / lopping that can occur with manual adjustable carbs.
A richened condition while choking a carbed bike feeds enough gas to keep it running as it warms. This causes the high idle to engage so you have a motor warming at a fast enough speed to keep it going while cold.
Of course once warmed, or as it's warming it begins to either die out from too much choke, or the idle speed increases, and then will decrease from the over-enriched condition from the choke. Metering off the choke as it warms, smooths out the idle and let's you know it's ready to go.
So when cold it does have a "lulling / lopping" or hesitating sound similar to the sound of an aftermarket cam.
A richened condition while choking a carbed bike feeds enough gas to keep it running as it warms. This causes the high idle to engage so you have a motor warming at a fast enough speed to keep it going while cold.
Of course once warmed, or as it's warming it begins to either die out from too much choke, or the idle speed increases, and then will decrease from the over-enriched condition from the choke. Metering off the choke as it warms, smooths out the idle and let's you know it's ready to go.
So when cold it does have a "lulling / lopping" or hesitating sound similar to the sound of an aftermarket cam.
Stellar HDF Member
Joined: May 2009
Posts: 2,856
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From: Middle of Kansas
I changed the pilot jet from a 42 to a 45 on my 99 FXSTC. I now start it with the enrichner pulled out, and after a few seconds push it all the way in, and use the throttle lock to keep it at a good idle. It sounds much better at idle both cold and hot.
Elite HDF Member
Joined: Sep 2007
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From: Bluffton, South Carolina
First check for air leaks,don't forget the vacuum hoses. Then make sure that the enrichner cable is fully seated in the carb. Ensure that all the throttle cables/linkage/etc are not sticking. If all is well there then try going larger in the pilot jet, and turn the idle mixture screw 2 1/2-3 turns out from being seated gently. (Disclaimer: That is if all other mechanical and electrical components are functioning properly.) Hope this helps.
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