Reply to edp.
Ya I've got a 1200. Had to come to this site to see what a Datsun 110 cp looked like, sad I know.
I was fighting with a simler issue a while back.
Traced it down to a vac leak and a Ign part that wasn't grounded.
I had TUNED out the vac leak when I first got the car, thought it was just bad gas ( sat for over 6yrs) I only moved it around the driveway, so didn't worry about it.
Still has a bit of a flat spot at 2-3k rpm, otherwise it runs fine.
i planed to pull the motor for something with a few more cc's, so the stocker was of no consern. Drive it every so I've learned how to tune it.
Guess that was a bit off topic.