Mikuni VM29 Smoothbores

So I have bought a set of VM29's. I decided to go this way instead of a new set of flat slides or Kehins to keep it all period in appearance. Carbs have been ultrasonically cleaned and look pretty good.

I put them on the bike Saturday and gave them a run. Seem to ride really nice. Very happy with the on road performance. Only had a short ride as I am waiting for the pod filters to arrive.

My problem is an erratic and hanging idle. Bike idles high for a while then wants to stall. Blip the throttle and it idles high again then wants to die.

I changed the inlet manifolds to some new ones, as the originals looked a little cracked, just to make sure there are no vacuum leaks. Seemed a bit better but still idles high and eventually dies.

Any suggestions on what to look for?
Thanks

Missing filters causing a really lean mixture seems a likely possibility.
Carburetors not properly synchronized and adjusted could also do it.
Maybe problems with a throttle cable.

Agree with doing a sync as the starting point.

I bench sync'd mine using a 1/32 brass rod and got em super close after checking with the Morgan....... they don't like to be much off from 3/4 of a turn out on the air screws too.

Thanks for the tips. I will check the sync at some stage. Bike is in a display this weekend and I am away the one after. I have new cable to fit so will check adjustment then.

Been told not to try syncing with the carb tops off. Is this correct?

I've read that too (on the syncing) but some others have disagree'd....... the half a dozen times I've bench shimmed them I've gotten them so close there was no need to change em after checking with the gauge.

The only way to vacuum sync them is with the tops off. I do it all the time with my 33 smooth bores. The big fours are more forgiving with out of sync carbs. The smaller ones make the devil's own noise with them slightly out of sync.
Steve

I rode the bike home today from the show I mentioned. Apart from the erratic idle, it was also popping in the exhaust lots at idle. Similar at part throttle on the road. Cleaned up once out on the highway with the revs over 4500. Started popping again when I slowed back down coming into town.

Is the popping indicating a rich mixture? Carbs were setup with my rebuild in mind so wondering if they are way rich with 0.9 air jets, 17.5 pilots, 120 main, 5DL31 needles on the 3rd clip, air screws 1.5 turns out. Pilots could even be 20's - I haven't checked them.