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Join Date: Nov 2007
Location: Chandler, Arizona
This sounds like a diaphragm issue. An air leak is generally constant. The slides may be moving while the engine is idling. Even with everything perfect, it is much more difficult to get a really smooth idle with a CV carb than a real carb, because the diaphragm setup is too sensitive.
One thing you have to remember, is that when idle speed changes up and down, something in there IS moving. It is not likely the throttle, as it has a pretty strong spring on it. Make sure you have a consistent supply of fuel to the carb. Remove the pilot screws and spray some carb cleaner in there, then put them back at about 2 1/2 turns out. A too lean (or too rich) idle air/fuel mixture will cause a fluctuation at idle, but not 500 rpm. It is also possible that you still have a intermittent problem with the needle valve. It would be interesting to hook up an emissions analyzer to it and watch it as the idle goes up and down. BTW, what kind of carb cleaner did you use? I use Gumout for carb cleaning once the carbs are apart, but any type of keytone based carb cleaner like Gumout can damage plastic and rubber parts, especially if you soaked them in it. Seafoam on the other hand is harmless to plastic and metal. You can get it in a spray can with a straw.
I am a motorcyclist, NOT a biker.
1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike