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Discussion Starter #1
Mikuni BS34SS Twin Carbs

Cold bike:
Idle screw 1/2 turn above "normal" and the bike fires right up with full choke. Back the choke off as it warms and bike idles as it should.

Ride the bike 10 mins, engine is now at full temp, idle is double what it should be...back idle screw off 1/2 turn and it idles/runs perfect.

Once the bike is cold again...if I leave the idle screw where it should be...the bike will not start...screw it 1/2 turn above "normal" and it fires right up...repeat the high idle issue when hot.

Why the high idle at full temp, but not as it's warming up...and no start when cold with idle screw set for proper hot idle?

Thanks!
 

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I know it's been a while, but have you checked the O rings between the intake boots and head? it's pretty common for them to go bad and cause a "hanging idle" like what you describe
 

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Discussion Starter #3
You're close, but it was a faulty petcock that was allowing gas to flow through the vacuum line.

When the bike was cold, it acted as a primer; but when hot, it added more fuel than necessary...high idle.
 
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