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Old 10-06-2015, 08:33 PM
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Davezilla Davezilla is offline
Motorized Bicycle Elite Member
Join Date: Mar 2014
Location: San Antonio Texas
Posts: 2,710
Default Re: Idles strong at first, then not so much

I agree with crassius to set the idle mix and speed with the engine fully warmed up and just blip the throttle to keep it idling when cold and as the engine warms up.
the best way to set the idle is by adjusting the idle mix screw in until the engine starts to stumble on the lean side, then slowly adjust out to the rich side counting the turns until it stumbles on the rich side, then go back half way to the lean stumble point, this will put the mixture where the engine wants it and not where the EPA wants it (lean stumble, then back off 1/2 turn).
the idle mix on the mikuni carbs also plays part in the cruise mixture so getting this adjustment as accurate as possible can really help the bike with its low speed manners. Mikuni also makes 3 different throttle slides for these carbs but they can be hard to find to buy individually, but the slides can be trimmed with a dremel or with the sandpaper on glass trick to help richen or leaning the off idle mix, I wouldn't sand or file on the slide bottom tho unless it simply won't tune without doing so, but it is an option.
Also, if your engine isn't fully broken in, you may need to readjust your idle mixture a lot as the engine loosens up and the rings seat better.
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