Mikuni HSR idle erratic
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Road Master
Joined: May 2012
Posts: 1,001
Likes: 107
From: Houston
Mikuni HSR idle erratic
Hello. Been playing with the carb on my 1997 Fatboy. I've noticed the idle will be nice n Lopey then speed up a little making a different sound then go lopey again. Nothing to crazy but I notice it. Air screw adjustment maybe? 2 turns factory setting. Screw in till change, screw out till change then set half way?
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Road Master
Joined: May 2012
Posts: 1,001
Likes: 107
From: Houston
The rubber
the rubber piece that holds the carb to manifold is good. So maybe I need to rebuild carb? New orings and such. I wa thinking air may be getting in around where idle screw goes into carb.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
That said when my S&S E developed an erratic idle it was because of a worn out accordion piece of rubber on my accelerator pump shaft.
Look at your diaphragm and all rubber parts is what I suggest.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
Likes: 2,159
From: Ohio
There is a rubber cap that covers a vacuum port on the Mikuni, it cracked and changed the idle, happened in Sturgis along with a broken choke inlet fitting.
Got to pull it to get to that cap so go ahead and rebuild it, simple but great carb.
Got to pull it to get to that cap so go ahead and rebuild it, simple but great carb.
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Road Master
Joined: May 2012
Posts: 1,001
Likes: 107
From: Houston
Vac cap
Are you referring to that port on the back towards the front cylinder? I saw a black cap on there but did not inspect it. Earlier I carefully sprayed the carb in certain areas w carb cleaner and bike would start to stumble. I couldn't exactly pin point where. It seemed as if it was just getting sucked through intake so it was hard to pinpoint like I said.
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Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
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From: Ohio
I believe so, just remember on the back side of the carb. Honestly would put the intake manifold seals on it also, they are known to cause some goofy idles and hard to diagnose. Put dish soap on the intake rubber seals when sliding it back together, slick when going together and dries not swelling up the seals.
