I had the same kinda issue with my carby'd one

Turns out i had a few issues including the old fuel pump was on the way out (cheap to replace) and it had a kinked rubber fuel line - might be worth a look.

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Currently own...

B210 120Y Sedan - FJ20ET Race Car Build
H230 Wagon / Van - LD28 Turbo powered - restoration to start

Blow-by fouled plugs shouldnt konk out a 6 cyl completely dead that consistantly but flooding will.
Yes you can clean plugs with a wire brush and refit. They are pretty robust.
Common causes of low/rough idle are things that affect the air+fuel+ignition mixture:

Split vacuum hoses/fittings on intake,
Blocked fuel filter/lines,
Faling fuel pump,
Blocked/rusty fuel tank (old fuel).
Faulty efi sensors (CAS, Coolant temp, Air temp, AFM, TPS, MAP),
Corroded efi plug/connector terminals (Engine temp, Air temp, AFM),
Faulty FPR,
Jammed EGR,
Sticking AFM,
Broken PCV,
Failing CAS/Ignition module,
Dirty/leaking fuel injectors,
Shorting leads/ignition coil,
Worn dizzy cap/rotor etc...


Most old datsuns burn oil thesedays. Dont sweat it, just keep topping her up...

I would be lening towards coolant temp sensor over fueling the engine by runing it in cold mode at all times or maybe ignition module braking down.