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1980 Datsun 720 L20B failed smog, running rich


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I recently inherited a 1980 Datsun 720 pickup truck from my father. Truck has 40k miles and is in overall good condition. The problems that I currently have with it is: 


Runs rich and backfires,


Failed Smog


High idle ( about 1500 rpm)


Vacuum hoses disconnected everywhere

From carburetor, smog pump, and air filter housing


1 nut that holds down carburetor is missing

( Can somebody give me the size of the nut)


Carburetor choke doesn't move at all when gas is pressed


Things I have done or changed on car

- pcv valve

-spark plugs and wires

-distributor cap and rotor

-oil change

-new air filter

-new smog pump filter

-new carbon canister filter


I am not mechanically inclined when it comes to carburetors , any help is appreciated.


What should my next course of action be. I am thinking of going to a carburetor mechanic at this point.


I will upload images of both the truck and engine bay when I get a chance later


I just want to drive this truck 😭









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L motors are simple.

Post a photo if possible so we see what maybe is obvious.

later L motors were full of emmissions equipment(hate that shit)


choke should be closed when you first start the car as its cold then as the 12volts warms up the heater coil it will push the choke flap open over time.

so maybe that's why your running rich as the choke is still on.or someone removed the 12volt wire


you have a timming light also?

Edited by banzai510(hainz)
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Go to e-Bay and buy a 1980 720 Factory Service Manual (FSM) from Nissan, NOT a Haynes or Chiltons. Get the Nissan produced FSM. Probably around 20-40 dollars. New they are $75 so don't pay too much for them. The first hour of mechanic's labor you save will pay for the book about 3 times over.


Running rich...


Choke is on all the time, not shutting off. Could just be dirty and stuck. Liberally spray the linkages with WD-40 and hold the throttle half open while you move and free up all linkages. Electric choke heater may not be working or no power to it. Choke will carbon up the combustion chamber and the plugs causing hot spots that can also cause backfires.

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