Nissan Bluebird automatic choke

The heater element (if it's the same as the Sunny was) on the carb opens up the choke gradually and is prone after 10 years or thereabouts to going intermittent. The cause is the aluminium rivet holding the external terminal becoming loose and tarnished. I fixed mine by taking it off and peening the rivet a little with a centre punch to make a tighter connection.

Another thing that can happen is a vacuum diaphragm splitting, these can be tested by pulling off the rubber tube and sucking on it, the metal rod attached to the diaphragm should pull in firmly. I'm not sure if this part is replaceable, I fixed mine by replacing the rubber diaphragm with a bicycle puncture repair thin rubber patch (the 'cut your own patch from a roll' type). A scrapyard raid may be easier.

The actual auto choke mechanism shouldn't have gone out of adjustment much if it hasn't been stripped down at all, you would have noticed the cold idle speed changing gradually over the years if it was this.

Brilliant - thanks, will try both these to see if I can track down the problem