Divvy Trouble

[ChrisG]

The wife's Diversion 600, which has has a vacuum fuel tap, seems to run fine when set to Prime, but if I set the tap to Main it seems to run ok (rode it a couple of times around the block) with some revs on but conks out at idle.  I've fitted a new seal kit to the tap, which seems to have cured the small leak but not the conking out.     All I can think of is it's somehow not getting a good enough vacuum at low rpm to keep the tap open, but I've just checked the neighbor's Divvy and the vacuum line is connected up the same, seems to be tight both ends and no obvious splits.

 

Any other ideas?