78 750 still will not run with choke off

[dumbar]

This set of carbs has a second set of hoses connecting the bodies of  the carbs.  there is also an open fitting coming out of this set of conecter hoses that is connected to nothing. I have a second set that has only the one set of connection hoses located toward the rear(or inlet side).other than that the carbs look identical.  The engine runs fine with the second set, but still will only run if choke is on with the first set. I think both sets are 78 (Keihin). What is the purpose of the second set of connector hoses and should the outlet be pluged or conect to ?what?.

[TOOLS1]

The set with only one set of hoses is a 76 model. On the other set the hose does have to be connected to something, or plugged. With it open it is creating a vacuum leak. This would cause it to run lean, requiring less air. Hence only running with the choke on.
TOOLS

[Re-run]

I can shed more light on this.
On the 78 carbs, you have 2 tubes between each carb. So, for instance, there are 2 tubes between 1-2, 2-3, & 3-4.
The thicker metal ones are your main fuel rails that feeds the carbs from the fuel line.
The smaller rubber lines are also fuel rails but they are for the accel pump to push fuel to the brass nozzles in the carb openings.

You have 2 hoses that come off from the carbs. 1 is the fuel line to the tank.
The second is a vent line that does not need to be plugged. In reality, that smaller fitting would have a hose on it that then lays across the top of the airbox that does not plug into anything. So, do not plug it but have a hose on it that lays across the top of the airbox.