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Forearm of Steel
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2,599 Posts
Discussion Starter · #1 ·
Noticed a unusually high idle (1800-2200 rpm) the other day, and I went to look at it and my throttle screw wasn't working. Well I fiddled again with it tonight and the screw actually fell out. After a few minutes of frustration, I found the place it went and screwed it back it, but just barely. I started the bike up and it still idles high... I screwed it in some more and got it dial back to where it barely affects the idle, but the idle is still high. Anybody know what could be happening?

I didn't have time to really check it tonight but the throttle cable seemed to have enough slack in it.
 

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sickboy
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3,546 Posts
The idle mixture screw is just a very fine adjustment to the fuel/air mixture at idle to create a smoother idle. Anything that changes the the normal mix of air/fuel can render that adjustment useless. A vacuum leak at one of the boots, gummed up air or fuel passages in any of the carbs idle passages, even a throttle plate that doesn't return to the fully closed position can affect it.
If the bikes been running fine and all of a sudden is doing this then id look for a vacuum leak first.
 

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Forearm of Steel
Joined
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2,599 Posts
Discussion Starter · #3 ·
The idle mixture screw is just a very fine adjustment to the fuel/air mixture at idle to create a smoother idle. Anything that changes the the normal mix of air/fuel can render that adjustment useless. A vacuum leak at one of the boots, gummed up air or fuel passages in any of the carbs idle passages, even a throttle plate that doesn't return to the fully closed position can affect it.
If the bikes been running fine and all of a sudden is doing this then id look for a vacuum leak first.
It's not the idle mixture screw on the carb, it's the idle adjustment screw that makes the idle go up or down depending on how much it's screwed it. It moves the rod the butterflies inside the carb are attached to.
 

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Premium Member
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1,336 Posts
Your pull throttle cable is likely too tight. It's got tension on it all the time, so even fully "closed" is leaving the throttle butterflies open a bit. Put your idle adjust screw to where it just starts to affect the engine speed again and then loosen the hell out of the pull cable. Adjust your idle to where you want it, then gradually take up the slack in the pull cable until it's how you like it.
 
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