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Emission controls, first introduced in the US in 1964, have proven over time to be a good thing -- today's cars have very low emissions, but super-high power (in fact, they have more horsepower than pre-emissions cars). However, some of the early systems hurt engine performance, including some of those used by the Datsun 1200.
Contents |
Overview
The four types of pollution targeted by 1971-1973 controls include:
- Gasoline vapors (EVAPO system), This means gasoline fumes escaping from the fuel tank, engine or any other part of the car
- Unburned Hydrocarbons (HC). Basically this means partially burned gasoline. Not only does it smell bad, it is toxic, cancer causing and contributes to smog. In a perfectly efficient engine, all HC would be converted to water (H2O) and Carbon Dioxide (CO2). This would result in the greatest fuel effiency. Since unburned gasoline means bad fuel economy this is a good performance goal, as well as an emission-control goal. Note that engines produce maximum horsepower with a rich air/fuel ratio for various reasons, but this is bad for pollution. Most cars run rich at full-throttle (even new cars) since it is generally not a strict part of emission test procedures.
- Carbon Monoxide (CO). As we all know from the movies, carbon monoxide can kill you. In low doses it can make you sick
- Oxides of Nitrogen (NOx) were restricted starting around 1974. They contribute to smog and acid rain. First EGR was used in the 1974 B-210, then later to meet stricter requirements, Catalytic Convertors were adapted starting with 1976 California B-210s
Nowadays CO2 emissions which as a greenhouse gas appears to contribute to the global warming effect. But it was not regulated in 1971-1973 automobiles.
For more information on automotive emission control, see wikipedia:Automobile emissions control.
Emission Testing
Some states have emission testing in urban areas. California is notable, but many other states also have a yearly or bi-yearly requirement.
The good news it that no state is currently requiring a Datsun 1200 to be tested. Datsun 1200s were made for model years 1971-1973 and so are past 25-year rules (e.g. Washington State) and 32-year (California) rules.
However, if you import a newer Datsun 1200 truck into your country, it will be subjected to the 15-year rule (Canada) or 25-year rule (USA). Vehicles newer than this will be required to meet emission control standards using a smog test.
Controls used by Datsun 1200s
Datsun 1200s in different markets came with different emission-control equipment. Some markets had minimal controls (those related to performance, like PCV) while USA models had the most controls to meet pioneering California rules.
Significantly, no Datsun 1200 came with:
- EGR (used on B210)
- Air Pump/Smog Pump (used on B210)
- Catalytic Converter (these first started with 1976 models)
- high-temperature engine thermostat (212-degree)
Exceptions may be later-model Datsun 1200 trucks.
Australia Models
- PCV system
USA Models
Datsun 1200s came with:
- PCV system
- Evaporative System (fume control)
- Revised Spark timing (engine ignition timing)
- Revised carb jetting
- Idle-return spring on carburetor. This is both an emission-control feature and a safety feature
- (1972-1973) Throttle Opener
- (1972-1973) Automatic Choke
- (1973) Higher Idle speeds
Details
PCV System
Positive Crankcase Ventilation (PCV) was the very first of the emission controls. It aims to prevent the crankcase from dumping fumes right into the atmosphere. This is a good system, and can actually help power and fuel economy. Before 1964, cars had a 'breather pipe' that led from the block down to the underside of the car. Normal blowby gases were thus simply vented to the air. Worse yet, when the piston rings became worn, a visible trail of smoke could be seen eminating from the bottom of the car. Not only did it pollute, but didn't smell good either.
Black hose is the main PCV hose
Nissan calls its PVC system the "Crankcase Emission Control System".
The PCV system consists of three components:
- Simple vacuum-operated valve connected to the intake manifold
- crankcase breather hoses:
- from engine block to the air cleaner
- from rocker cover to the air cleaner
Fumes are thus routed to either 1) air cleaner when engine speeds are high and so able to 'suck' the fumes in or 2) intake manifold when idling where vacuum is high and so opens the valve slightly and pulls the fumes out of the crankcase. This is where the efficiency comes in. Since at idle the pistons are operating under low vacuum, the PCV valve equalizes the forces in the crankcase, hence less oil is sucked into the cylinders at idle.
Race cars are often required to use an oil/vapor seperator instead of, or in addition to, the PCV valve. The main purpose of this racing requirement is not to increase performance, but to control oil spills onto the race track surface.
CAUTIONS
As part of your Tune-up, replace the PCV valve if it:
- oil-soaked or crusted with sludge (sometimes it can be cleaned with ether spray or carb cleaner). The valve inside should open and close when you shake it back and forth
- Has a broken spring. The valve inside should close at rest, even if you hold it straight
EVAPO System (Fume Control)
USA models were required to control the amount of gasoline vapor that escapes from a vehicle into the atmosphere. The Datsun 1200 used an early system that consisted of a sealed gas tank, and hoses to route the fumes from carburetor, rocker cover and air cleaner to appropriate places. Be sure to use the original 1200 gas cap, which has no pressure vent (only an air inlet valve, which is normally closed).
For details on how this works in the Datsun 1200, see Fume Control.
Ported Vacuum Advance
Ported vacuum for the distributor is the carburetor fitting tapped just above the throttle plate. This gives zero vacuum at idle, but full vacuum at just above idle. This is not technically an emission-control method, and was used prior to emission control. However it does help reduce emissions. It is an OK system and there is need to remove it. In fact, hooking up the distributor to the intake manifold directly will cause problems with setting the correct initial timing, as the standard specifications are for ported vacuum.
Revised Spark Timing
For reduction in unburned HC, generally the spark timing is reduced from optimal-power settings. This results in a more complete combustion under certain part-throttle conditions.
Because this reduces power, engine timing is dynamically controlled by various means, including:
- Revised mechanical advance. The curve comes on late, with reduced total advance
- Revised vacuum advance. The curve comes on late, with reduced total advance
- Transmission Controlled Vacuum Advance System (TCVAS) A vacuum advance cutoff disables advance except in Top Gear
TCVAS
Transmission Controlled Vacuum Advance System (TCVAS) disables advance except in Top Gear. Since this "retarded" spark timing reduces performance, to prevent cold-engine driving problems this system is bypassed in cold temperatures. This means vacuum advance works normally at cold cabin temperatures.
In a normal system, vacuum goes directly from a fitting on the carb over to the distributor vacuum advance diaphragm. In the TCVAS system, there is a valve inserted into the hose to block/allow the vacuum.
The vacuum valve is electrically controlled. With 12V supplied, vacuum is blocked. From a performance standpoint, this is fairly foolproof becuase if a wire is disconnected it works with normal advance. Only when correctly wired does it block vacuum advance.
TCVAS Components:
- Special orifice-restricted hose between carb and tee-connector. This has a precision orifice (jet) in it to control flow of air
- Thermo switch in cabin, under dash mounted high on the right-side kick panel. This is a little round button-shaped unit. It is a simple on/off thermostat which turns "On" as temperature raises past 41-55 degrees. It turns "Off" when temperature falls below 34 degrees
- Electrical "Top Switch" screwed into the side of the tranmission (left side, near the bell housing). It is closed in top gear, open in all other gears and nuetral
CAUTIONS
- Using a normal hose from the carb to the T-connector results in a small vacuum leak. Only use the special orifice-restricted hose
Note that since Ignition Timing is set with distributor hose disconnected and plugged, a malfunction in the TCVAS will:
- not affect the Ignition Timing procedure
- not affect idle-speed setting
Throttle Opener
1972-1973 USA models use the Throttle Opener mounted on the carburetor to prevent the throttle from closing completely while the car is moving. This results in a drastic reduction of unburned HC. Carburetors are not efficient at high vacuum (closed throttle) high-speed conditions. So the Throttle Opener prevents this from occuring.
The Opener is operated by engine vacuum. When vacuum is supplied to the carb-mounted diaphragm, the 'phragm pulls a secondary throttle linkage which prevents the throttle shaft from returning all the way to idle.
To keep a smooth feel of the accelerator, the Opener only works at speeds above 10mph. This is accommplished by a vacuum switch mounted on the front of the intake manifold just in front of the carburetor.
The vacuum switch is operated electrically by an electrical switch in the speedometer. Thus there is a hose from the intake manifold to the switch and from there to the the Opener diaphragm on the carburetor.
When the speed goes below 10mph, the vacuum switch opens (12V "on"), and vacuum in the diaphragm slowly bleeds off through a small jet and needle valve in the vacuum switch. Thus the throttle gradually closes all the way. It is a smooth transition you won't even notice. The vacuum bleeds off by letting clean air enter from the air cleaner. Thus there is a small hose from the switch to the air cleaner.
In automatic-transmission cars, the vacuum switch is "off" in Neutral and Park (12V supplied to solenoid).
At idle, there should be 12 volts supplied to the vacuum switch/solenoid unit. Also it should be supplied with engine OFF, Ignition Switch ON.
CAUTIONS
The Opener used on the Datsun 1200 is fairly unobtrusive. It keeps the throttle slightly open during deceleration. Some newer cars made in the late 70s used fairly radical Openers that kept the engine at relatively high rpms and made for odd, highly noticeable throttle experience. So if you are using a newer carburetor, keep this behavior in mind.
Troubleshoot: Note that in the factory service manual, there are extensive procedures, diagrams, specifications and drawings. You should borrow, buy, or check it out from the Library.
Takes a long time to return to idle
- There is a screw adjustment on the solenoid. Adjust it to Nissan factory manual specifications. This is rarely a problem unless someone changed this setting. Normally it is set at the factory, and never touched again.
Idles noticeably high While Decelerating
- Adjust the Throttle Opener linkage on the carburetor per carburetor specifications.
Idles too high at Idle
The Throttle Opener is de-activated only when the electrical connections are working correctly. If the wires becomes disconnected, it is "on" which results in an idle-speed problem.
- If you have 0V to the solenoid at idle, one of the following is indicated:
- Auto trans Inhibitor Switch stuck "off"
- bad wiring, or wiring disconnected under-hood, or under dash
To test for proper electrical operation, connect a voltmeter to the switch with wires into the cabin. Use a voltmeter to read the voltage while driving. It should switch from 12V to 0V at approximately 10mph. you have 12V to the solenoid at speeds above 10mph, one of the following is indicated:
- electrical switch in speedometer is stuck "on"
- wrong speedometer fitted (one with no switch)
Vacuum Leaks
Lastly, since the Opener is operated by engine vacuum its parts are a potential source of "vacuum leak". See Vacuum_Leaks. If you suspect a leak, simply plug the port on the intake manifold:
- If the engine idles better, it indicates a bad hose, a bad vacuum switch or lack of 12V to the solenoid.
- Check hoses for cracks (especially at the ends), burns or other visible problems
- There is a one-way valve in the vacuum switch to prevent air from going into the intake manifold port. You can blow on the diagphragm side. If air comes out the Intake port of the switch, it is defective. Replace it or plug the intake port to disable the entire Opener system.
- If the engine runs better at speed, it indicates:
- a leak in the carb-mounted Diaphragm
- (less likely) a leak in the Opener solenoid
Revised carb jetting
To reduce the amount of Carbon Monoxide (CO) and Unburned Hydrocarbons (gasoline), carb jetting is carefully controlled to burn the gasoline efficiently. The advanced original-equipment Hitachi DCH/DCG carburetors were fairly good in this regard. For the US market they were modified slightly lean in part-throttle use to reduce emissions. In general, Datsun 1200 carbs are richer than newer Datsun carburetors. Full-throttle operation, not being tested by US law, remained rich.
However, after the Datsun 1200 years, the Hitachi was modified with more and more controls, increasing complexity and reliability.
Higher Idle Speed
Some models use a higher idle speed, higher than 600rpm. This allows more air through the carb at idle, and so the carburetor is better able to mix the air/fuel ratio. However it does cause two problems:
- Engine "run on", where the engine "diesels" (won't stop running) after the ignition is turned off. 1973 models compensate for this by using the anti-diesel valve (fuel cut-off valve).
- Increase noise. The A12 engine is much quieter at 600rpm than at 750 rpm.
1973 US models feature an "idle-limiter cap" on the carb's idle speed screw so that users won't accidently change the idle too much. This is primarily to control CO emissions. As the years go by and the carb wears and air leaks past the throttle shafts, it may be necessary to remove the cap to adjust the carburetor to a "good enough" setting.
Temperature Controlled Air Cleaner
Temperature Controlled Air Cleaner has two effects:
- Prevent carburetor "icing" in cold weather (near freezing to below freezing). Markets otherwise without emission control requirements used a simple "summer/winter" manual lever on the air cleaner air intake snout
- Keep the carburetor air at a constant temperature. This way the carburetor can be more effective over a wide range of ambient (outside) air temperatures. This is sometimes called a "hot air" system. Nissan calls it "Automatic Temperature-Control Air Cleaner" (A.T.C. Air Cleaner)
The hot air system not only reduces pollution, but by ensuring the carburetor is fed a constant-temperature air, it aids fuel economy as well. The carb can be tuned for slightly-lean cruising operation without be affected by cold temperatures. Only disable this system if you want maximum performance and are willing to re-jet the carburetor to match particular temperatures. Racers will sometimes re-jet for different days and track conditions.
The ATC system consists of:
- special air cleaner. The cleaner gas normal cold-air intake into the snout, but with a hot air intake below. A vacuum-controlled diaphragm motor controls a valve inside the snout and makes this system easy to recognize (look for a large 2" round diphragm on top of the snout)
-
- A special abestos or aluminum clad "hot air" hose (about 1-1/4 inches in diameter) going from the exhaust manifold to the bottom of the snout. Non-emission cleaners also have this for the summer position
- A special temperature regulating valve in the air cleaner proper. This modulates the flow of vacuum to the Diaphragm.
- Two hoses:
- One connecting the diagphragm to the ATC valve
- The other from ATC valve directly down to the intake manifold vacuum port
Automatic Choke
1972-up USA models used an automatic choke to better control air/fuel mixtures when the engine was warming up.
For details on the choke operation, see Carburetor Adjustment.
EGR
EGR (Exhaust Gas Recirculation) was first used starting with 1974 B-210 models. It recirculates a small portion of the exhaust back into the combustion chamber. Although this dilutes the the air/fuel mixture (reducing performance), the inert properties of the spent gas reduces burning temperatures making drastic reductions of Oxides of Nitrogen (NOx).
For a detailed explanation of EGR, see the AutoZine Technical School article.
Catalytic Convertor
Catalytic Convertor were first fitted to 1976 Calfornia-models B-210s then to non-California B310s generally around 1980 or so. The converter fits into the exhaust pipe system, and converts unburned hydrocarbons (unburned fuel) into less-harmful substances--namely water and oxygen. Early convertors were a restriction in the exhaust system, but newer designs are high-flow. New designs are not too bad of a system, although some use the Air Pump to supply extra oxygen to the convertor. You can simply replace the convertor with a straight section of exhaust pipe.
Which controls can be eliminated?
For a race car, any you want may be removed -- though some are good for the engine.
For a road car, it depends on the local laws. Here are some thoughts on the technical aspects:
- Positive Crankcase Ventilation (PCV): This is a good system, and can actually helps power and fuel economy. If you remove it, you should design an alternative system to keep oil out of the air, and oil fumes from causing sludge inside the engine. It is recommended to keep this for all street cars.
<li>Ported vacuum for vacuum advance is the carburetor fitting tapped just above the throttle plate. This gives zero vacuum at idle, but full vacuum at just above idle. This is a good system, and removing it (disconnecting Vacuum Advance) will result in poor part-throttle acceleration and fuel economy. Connecting the distributor directly to the intake manifold can cause timing setting problems, as the standard specifications are for ported vacuum.
<li>Fuel Tank vapor recovery: This is a good thing, as why let gas fumes get into the air? They are easily controlled by venting the tank and the carburetor float bowl to a charcoal cannister. See your Datsun repair manual for an explanation of the various schemes used over the years. Also see Fume Control.
<li>EGR (Exhaust Gas Recirculation) hurts performance, and should be blocked for a race car. The easiest way is simply to remove the vacuum hose and block it with a plug. For a more streamlined look, remove the EGR valve and replace it with a block plate, and the hoses that control it. No other change is need, however if your engine starts to "ping" (pink) then either fit a 160-degree thermostat or carefully tune the engine to compensate.
<li>Air Pump (aka Smog Pump). This takes power to run, so for an off-road car should be removed. Remove the pump, block the exhaust manifold opening for it, and block the air hose fittings that are on the air cleaner.
<li>Catalytic Convertor can be removed for off-road vehicles with no loss of performance. Simply replace the convertor with a straight section of exhaust pipe.
<li>Throttle Opener is a fairly unobtrusive system on Datsun 1200s. It is recommended to keep it intact on a street car. For racing, where a 'snap' of closing throttle is desired, or where the Opener is defective, simply plug the port on the intake manifold thereby disabling the entire Throttle Opener system. No loss of performance will result, though invisible pollution will increase.
<li>TCVAS. For full performance in off-road vehicles:
- connect a hose directly from the Carburetor's vacuum advance port to the distributor
- Plug the hose going to from the Flow Guide Valve hose to the the Vaccuum cut off switch
- Optional: Remove Vacuum Cutting Valve Solenoid. Tape over wires