Choke Operation and Adjustment

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Operation

Here is what to expect from a choke:

Choked fully closed When Engine is Cold

Manual

• With the dashboard Choke knob pulled all the way out, the choke butterfly on the carburetor should be fully closed.
• In normal operation, only when the engine is cold should the choke be partially closed (knob pulled out)

Automatic

• With engine cold, moderate temperatures, the butterfly should close 100% (open throttle slightly to 'set' it)

Choke fully open when Engine is Warmed Up

For a manual choke (cold or hot engine), with the dashboard knob pushed all the way in, the choke butterfly should be fully open

For an automatic choke (engine fully warmed up), the choke butterfly (looking down into the carb) should be fully open, as in the bottom part of this photo:

bottom: choke fully open

After warming up fully, if you manually close the choke butterfly, then the engine shouldn't idle correctly.

Choke Gradually Opens While Engine Warming Up

Manual Choke: Gradually push the knob in to open the choke butterfly. If you push it in too far, the engine may stall. If out too far, the engine "chugs" (runs rich). Experiment a little. Your goal is to make it run it's best. You will need to push the knob gradually in every 30 seconds or so until it runs well fully close (knob pushed to dash)

Automatic choke: as soon as the engine starts vacuum should pull the choke open about 1/8 inch, by the Choke pull-off diaphragm. Otherwise, the engine "loads up" (runs rich) immediately after starting and might even die again.

Adjustment

Automatic Choke

To adjust the automatic choke, slightly loosen the three screws holding the round part. Rotate it counterclockwise for more choke, clockwise for less. The nominal (initial) setting is on the middle mark:

auto-choke adjustment

OK, here's the secret:

1. Set it (engine fully cold) just tight enough to just close the choke completely when tthe throttle is opened. Since it depends on outside temperature, adjust summer and winter if necessary.
2. Then warm the engine up. Blip the throttle occasionally to let the choke open as the spring warms. If, when the engine is fully warm, the choke hasn't completely opened, there is a problem. Check the spring on the choke. If it don't have enough 'spring', by a new electric one. It's just wired to the IGN (full +12V, before ballast resistor).
3. Note the single mark on the cover. Initally it is lined up in the center, then final adjusted per Step 1. In the winter set it a mark or two tighter (following step 1). Loosen the screws to turn this.

Auto Choke Adjustment]

Fast Idle Adjustment

This should only have an effect when the engine is cold, as it is related to the choke. The engine should run fast when started, then as it warms up and the choke is gradually released (blip the throttle to 'set' the cam), it should run slower until as the engine warms more, it comes off the cam and has no effect on warm engine.

Fast Idle Adjustment

Adjust for about 1200-2000 rpm (cold) or to your preference. It should be fast enough to run good, but not too fast. While Nissan has a specification, really it depends a lot on how cold it is where you live. If everything else is adjusted correctly (timing, no vacuum leaks, etc), you should be able to take off immediately and drive the car without "warming it up". If it dies, use a higher fast idle.

Fast Idle Adjustment

Manual Choke

Manual choke adjustment procedure: There is no adjustment.

1. To start when cold, pull the knob out.
2. After starting, push the knob in a bit
3. While warming up, constantly push the knob in or out until it runs right
4. When fully warm, the knob should be all the way to the dash

The only thing to check regarding choke, mechanically speaking is: remove air cleaner and inspect:

• Knob all the way out: ensure butterfly valve is fully closed
• Knob all the way in: ensure butterfly valve is fully open

Wiring

1972 & 1973 USA 1200 models were fitted with an automatic electric-heated choke setup.

Choke harness wire = Red

This also uses a relay so wiring is slightly complicated. You can simply connect the choke to 12V switch ignition (e.g. the ballast resistor), but using a relay that cuts power when the engine isn't running (alternator stops) is the preferred solution.

See main article: Alternator Wiring - Automatic Choke Relay

Part Numbers

B110 USA 
14806-N2200 LABEL-AUTO CHOKE CONTROL

Also See

Choke Cable
Carburetor Parts