Motorcycle Repair: Overspeeding idle, suzuki gs400, throttle cables

Question
Hi Mark,

I asked you a question a few weeks ago and you sent me an email asking me to forward my question to your email address.

I have had a chance to work with the bike and I have a simplified version of the problem:

I have a 78 suzuki gs400 which sat for 12 years.

First i replaced points, battery, coils, plugs, etc.

I rebuilt the carbs, dipped them, replaced the rubber, synched them with a synchronizer, and fixed a few leaks i discovered (then re-syched).  Now there are no leaks.  Also adjusted the idle screw.  I replaced the throttle cables.  

So basically it will idle at 1500 until I hit the throttle, then it hangs at 4000.  I can bring it down to a normal idle by engine braking, and it will return to 1500.  It's like its got two idle spots, but it prefers to idle at 4000.  Plus, its running too rich (no surprise there): the plugs are all black (though they're pretty new).

The throttle is returning to position.  It isn't the spring or the throttle return cable that's the problem.

Can you send me your carb files and do you have any ideas?

Thanks for your help,
Jeremy

Answer
Hi Jeremy,

I will gladly send you carburetor files, but you must include your email address with your question.

When posting a question, AllExperts asks you for your email addy to notifiy you of an Expert's reply. However, AllExperts does not allow Experts to see the info you provide other than the actual text of the question.

I think some simple tuning will fix your MC's idling problem.

Respectfully,
Mark Shively