Mikuni 34mm VM - Starts fine w/enricher but chokes when taken off

 I have a Norton 750 Commando which had the Amals replaced with the
Sudco 34mm Mikuni.

When I received the bike, it had an improper throttle cable which
caused the motor to race to full throttle the first time I started
it.  (Didn't try that again).

Replaced cable.

Now the bike starts easily with the enricher on...first or second
kick...idles cleanly.  As soon as I attempt the pull the enricher off,
the bike start choking and dies immediately.  This is not a "motors
too cold to take enricher off" choking, but definitely an improper or
insufficient fuel mix choking.

Obviously, I'm not a Mikuni expert.  I'm just trying to get some ideas
on what this might be.

Any helpful hints?  Needle adjustment possibly?

 deucewildwood wrote:


Turn the air screw clockwise to richen the idle mixture. If that doesn't cure
the problem, the idle jets are plugged up or the float bowl fuel level to too
low.

The Sudco Mikuni Carburetor, Parts and Tuning Manual suggests also cleaning
the "low speed air bleed". They are probably talking about the cross-drilled
air emulsion holes in the needle jet.

When the emulsion holes get plugged up, air and gasoline don't mix until they
get into the throat of the carbs, and even then the larger droplets will
settle out and you don't get the finely atomized fuel droplets that make
Mikuni carbs so much more responsive than old Amal Monoblocs.

The idle jets may also be cross drilled for air emulsion, but I can't tell
without knowing which jets were included in the build.

Sudco International has an online manual for slide valve carbs. Do you have
the 001-251 kit?
The people had Sudco can tell you exactly what jets and needles went into the
custom build for those VM-34's.

A slide valve carb does tend to get fuel past the needle sooner than a CV
carb would get it, but the
carb really doesn't come onto the needle until it's lifted quite far out of
the needle jet.

Some needles aren't even tapered for the first inch, so opening the slide
doesn't do much to richen the mixture.

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