Mikuni carb trouble

I recently reassembled my bike after 6 months.
When I flip the choke on - SINGLE MIKUNI CARB - the bike fires up first kick every time. However, when I flip the choke off it idles rough and dies. If I turn the throttle - it's sporadic. Sometimes it will rev way up to 4 or 5 and stay there for 20 seconds and slowly come back down to a rough idle. It will not restat without the choke on. So, I have to turn on the choke, kick it, and then turn off the choke. Could this be a bad throttle cable. The mixture seems good. I kept it the same as when it was running excellent. the carb has been cleaned out twice. Not sure if it's just a bad cable routing since it revs up and stays. The cable feels and appears to move fine. the needle moves up and down smoothly.
thanks

Low voltage to Boyer Brain timing.
Bad spark plugs.
Water in the fuel tank refiling fuel bowl.

checked all those
thanks for the input

Remove the idle mixture screw, after counting the # of turns out, drain float bowel, shut off fuel, squirt some Gum-Out, or similar carb cleaner into the orfice, go have a beer, come back and blow 60 psi air through the idle circuit--through the exposed orfice, replace idle mixture screw and reset adjustment. You may have to repeat this at least once more.

RS

thanks
cleaned out carb twice and replaced fuel
i think i need to reroute cable -

Maybe the slides sticking?

Could be sticking open causing it to stay at 4,000, then starts to work its way down?

Or,

Maybe time for an extra or new spring? I know some guys add an extra spring.

jsouthard said:

Maybe the slides sticking?

Could be sticking open causing it to stay at 4,000, then starts to work its way down?

Or,

Maybe time for an extra or new spring? I know some guys add an extra spring.

Click to expand...

It does sound like slide sticking. Me like a number of VM Mikuni owners added an Amal spring inside of the Mikuni spring to prevent throttle sticking at upper revs. Mine had stuck at a dangerous moment.
However since this is a problem that showed up after a rebuild and it worked OK before maybe rerouting cable to minimize drag all that is needed.
Any chance the screw on the hand throttle is snugged a bit too much adding to the difficulty of the spring closing the slide.

Bob

thanks for the post
the slide seems to move easily and evenly. maybe it gets snagged just enough to mess up my idle. However, not sure why this would affect the starting the of bike. Once warmed up, it always starts first kick with the choke off. Now i have to flip the choke on to start and then turn it off. But as soon as I do - it's hard to hold an idle
i'll try to lift the tank and reroute the cable. I recently had the tank off so this might be the problem.

I think there was another thread about this same problem and the answer was that the extra spring was really needed because the vacuum created by the Norton was preventing the slide from coming down. Everything looks fine when the bike is stopped, but when it is running the succion keeps the slide glued to the carb body.

Jean

Assuming you have the timing ect. correct, hard to start, requires choke to start, then runs like crap, I would be looking for an air leak, but do make sure your float height is correct.
As for the extra springs, probably not going to help you at the moment

thanks for the reply
i'll look for an air leak - really only one place it could come from - the rubber boot that connects the carb to the manifold. But it seems like it's in good shape. no cracks.
i'll also try the extra spring - just because i always like an easy fix.