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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)
- Unburned Hydrocarbons (HC). Basically this means partially burned gasoline. 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
- Oxides of Nitrogen (NOx)
Nowadays of course, CO2 emissions are attributed to loss of the ozone protective layer around the Earth, and contributes to the global warming effect. But it was not regulated in 1971-1973 automobiles.
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 timing)
- Revised carb jetting
- Vacuum advance cutoff switch for high speed operation
- (1973) Idle speed-limiter Cap on the carb, along with high 800rpm idle (650rpm for automatic transmission)
- Idle-return spring on carburetor. This is both an emission-control feature and a safety feature
- (1972-1973) Throttle Opener
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, US 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 engine 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.
The PCV system consists of three components:
- vacuum operated valve connected to the intake manifold
- crankcase breather tube, generally from the engine block to the air cleaner
- breather hose from rocker cover to the valve
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.
Evaporative 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 vent.
For details on how this works in the Datsun 1200, see Fume Control.
Revised Spark Timing
For reduction in oxides of Nitrogen (NOx), generally the spark timing is reduced from optimal-power settings. This results in a cooler burning engine, and resulting high temps that cause a massive increase in NOx pollutants.
Because this reduces power, engine timing is dynamically controlled by various means, including:
- Revised Vacuum advance. The curve comes on late, with reduced total advance
- Vacuum advance cutoff switch - disables advance in Top Gear
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 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 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.
Idle Speed Increases
Some models use a higher idle speed, higher that 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.
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.
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.
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 Carburetor Troubleshooting. 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, or possibly a leak in the Opener solenoid.
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 an OK system, no need to remove it or using full-vacuum advance. In fact, hooking up the distributor 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) was fitted starting at around 1974. This one 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. For a detailed explanation of EGR, see the AutoZine Technical School article. <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: First fitted to B310s 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 have high-flow. 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. <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. </ul>