High RPM at idle after carb clean

[sean.conaway]

Just took off and rebuilt the carbs on my '96 Nighthawk.  Got everything put together.  She starts and idles fine, but the moment I give her gas, she revs up and stays revved up - the idle doesn't drop back down.  I've ensured that the bystarters are closed and the throttle plate position is at closed on the carbs.  The only problem visible is a slight sweating of gas around the bowl on carb #4 (nothing a good tightening won't fix).  Y'all have any ideas what's up?  Much thanks in advance.

[ariwhiteboy]

I'd be willing to bet either A) somthing was not back together right or B) both throttle cables not attatched.


  to the forum by the way!

[Handyman1018]

Sounds like a cable issue to me.  Make sure they are connected properly and that there are no kinks in the routing of the cables.  Check the return throttle cable (I assume your bike has one) if this is not connected properly it could be the reason the idle does not return when you let off. 

[sean.conaway]

All cables are properly connected and routed.  They function perfectly.  When the throttle control is in the closed position, the throttle plate on the carb is also in the closed position.  When the throttle control is in the fully open position, the throttle plate on the carb is in the fully open position.  She will start and idle normally, but when I twist the throttle, and the throttle plate returns the closed, she stays high revved and sometimes actually starts to climb.  It's like the bystarters are open, but they, too, are in their closed position.  Possible the floats aren't arresting the flow of gas properly?

[Laminar]

Check for vacuum leaks and do a dynamic carb sync.

[Bumblebee]

Possible the floats aren't arresting the flow of gas properly?

Not likely. Floats maintain the proper fuel level in the float chambers. The don't directly control fuel flow into the engine. There would be a big delay in the order of multiple seconds followed by going rich or lean and probably quitting, not holding the RPM high like you're describing.

Mechanically:
Are there vacuum slides in the venturi on that carburetor? If so, one or more could be sticking when in the up position or the return spring on them wasn't installed.
Alternate air system or choke choke could be the problem.
Did you separate the carburetor bodies by taking them off the rack? If so, if the rack bolts are not torqued properly, it's possible the rack is twisting slightly when it's installed resulting in a substantial out of sync situation. The annoying bit is that they can be synced properly before installation, messed up when installed due to torque applied by the intake boots and when they're pulled back off, they're back in sync again. Grab the outer two carburetor bodies and twist by hand and see if the throttle plates move - they shouldn't.
Did you verify there are no intake air leaks? Air leaks can cause all sorts of problems including rpm hanging high.
When you cleaned the carburetors, did you set the pilot screws to book numbers or leave them where they were set? If the carburetor was actually dirty, cleaning it changes the air and fuel flow through the plumbing.

What is the idle RPM and what is the RPM it's hanging at? If you leave it idling high, does it eventually drop back down or remain there indefinitely? If it idles high then drops back down to the original idle RPM, it could be due to a lean air mixture. Open the pilot screws 1/2 turn out to eliminate the lean condition and see if the RPM hangs high again.

[sean.conaway]

Thank you all so much for your replies. . . The problem was much, much, much too boneheaded for your expertise.  Anyone know how to say me olvidé de ver si el tornillo de ralentí se ajustó in English?  I do: I forgot to check the adjustment on the idle screw.  Had the darn thing jacked in too far and was thus exposing too many of the pilot / enriching bores.  Dios mio.  Got it fixed, and man is she happy now: new plugs, new air filter and clean carbs really maker her want to go.

[ariwhiteboy]

Yep rule # uno...always check to make sure the nut between the seat and the handlebars didn't come loose and do something dumb!   

Glad you got it worked out!

[SirSeanSean]

When I was reading the first post, my first thought was if you checked the idle screw. A few post down and that is what it was. Glad that you got it sorted out.