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| = Operation = | = Operation = | ||
| Here is what to expect from a choke: | Here is what to expect from a choke: | ||
Revision as of 18:05, 28 December 2007
Contents |
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 setting is on the middle mark:
auto-choke adjustment
OK, here's the secret:
- 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.
- 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).
- Note the single mark on the cover. Normally it is lined up in the center, and in the winter a mark or two tigher. 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 & Dashpot
- The Carburetor Dash pot is used on auto-choke models.
Manual Choke
Manual choke adjustment procedure: There is no adjustment.
- To start when cold, pull the knob out.
- After starting, push the knob in a bit
- While warming up, constantly push the knob in or out until it runs right
- 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
Elecric Choke
- Red wire - To electric choke relay Y wire, and on through to the Alternator/Regulator "N" terminal. This supplies voltage only if the alternator is spinning, so that the choke doesn't heat up just from turning key to IG. The auto choke heater only heats up if the engine is actually running -- if it is turning the alternator.
The factory 1200 auto choke setup (1972 & 1973 USA models) uses a relay:
- Red - to choke
- Yellow - to "N" wire of regulator/alternator
- Blue (L) - to Fuse 10A in fuse box IGN side
- (also to Anti-diesel valve on 1973 carburetor)
- Black - to ground/earth
Location of Choke relay:
To left of radiator
All this being said, you can simply hook the choke up to the Hot side of the ballast resistor -- it seems to work fine. The only downside I've observed is when you can't get the engine started right away, the choke heats up while you are trying. So using the alternator output and a relay is a better idea.