A basic tuneup is not always the answer on a 33 year old car, which it sounds as if it has not been cared for properly. Not everyone understands basic car mechanics and it cannot be explained to them by reading a manual which was written in technical terms for a person with a fair bit of knowledge. I thought that this and all other forums were designed to help out the people that need to get along in life without being treated like a moron or a drag on our time. Back to your "77" you can fiddle with all of the adjusting screws but it won't cure the problem of why it went from runnig fair to poor, no one went under the hood and adjusted them while you were not looking, you have to find the source of what caused that change. This brings me back to the earlier posts if you would like to read over them again. I hope you are able to solve your Datsun issues, as for myself I would be glad to respond to any future posts you may have.