Nissan Repair: 1987 Nissan Sentra misses and backfires, nissan sentra, power valve

Question
Manual transmission, starts fine, but misses and backfires when you start moving. It's worse going uphill than down.
I had the carburetor rebuilt (with aftermarket parts) because of this very problem, it ran fine for a month and is doing it again.
What next?

Answer
Valerie,

Either the power valve has gone bad or there is an obstruction in the carburetor.  Those would be my first thoughts.  Other areas of concern would be that the plugs are fouling or the ignition needs to be diagnosed.  Cap, rotor, wires and coil need to be inspected and verified that they are in proper working order.