It is not a problem of sensor as it is not showing any dashboard light, neither it seems to be a problem of battery as battery gets charged after driving if the alternator is working fine or otherwise it won't start at all after overnight standing. It could be a problem of starter solenoid as it has copper windings and when the copper winding gets old it functions intermittently. I am sharing a video that will explain it better.
GA13DS is carb,
the spark timing for most cars like this is -5Deg BTDC
the adjust in more timing based on fuel used, (more NEG)
the better fuel allows more advance, until it just starts to Ping under load,and back of a TAD. (based on OCTANE FUEL USED)
we did that for 60years, 1920s to early 80s. did my first at as boy 1962.
Question edited for clarity.
Question moved to Nissan Sentra.
No problem. When you depress the clutch, you remove the load from the engine to the cogs and shafts in the gearbox.
Engine - Clutch - Gearbox workings - Wheels
Just make sure that your oil levels are correct. In a manual car you can additives like Molyslip to the gearbox.
The fuel pressure regulator will be on the fuel rail. This is a long rail that connects to each fuel injector. On the sentra, the fuel rail will be behind the valve cover on top of the intake manifold.
