mikuni carb fix

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hello every one this is my first post so here goes. appreciate any help.
i have a 1973 commando roadster with a 34mm mikuni carb. am trying to restore it. it runs well at idle but sticks open when throttle turned. tryed stretching the return spring no help. when the engine is not running throttle and slide work fine. seems like vacumm of engine running won't let slide drop. any ideas?
I have modifyed my Mic with a UFO and it does not stay on the screw. You can add an old Amal return spring inside the mic spring. It works every time now, Just be sure there's no slide bind causing the root of the problem. norbsa
thanks norbsa, will try. what does ufo and stay on the screw mean in the context of your post?
UFO, ultimite flow optimizer it's a hunk of plastic that when inserted into the base of the slide smoothes out the cavity. The thing is sold by Thunder Products invented for snow machines.
On the screw means the slide has settled and come to a stop on the idle seting screw. norbsa
Need second spring

I had this exact problem on my '72 with a single Mikuni. One day it just started sticking open. I opened the carb several times and couldn't find any stickiness. Called Rocky (Mikuni specialist) and they suggested a second spring. They sent me one, I put it in there, and the problem disappeared, never to return. That was maybe 6 months ago. And the throttle is still very easy to open.

thanks guys i'll be putting in spings, as you suggested, and let you know how i make out.
put in the 2nd mikuni return spring. everything works fine. thanks for the help norbsa and stuart.
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