GROSS POLLUTER - Failed Cali Smog test

[Nicholas7620]

Hi Everyone,

 

I failed my biannual smog test because my rebuilt Hitachi Carburetor is running too high CO's, which means too much fuel is getting through.  The carburetor is running too rich.  HydroCarbons are low.  Nitrogen Oxides are low.  The Carbon Monoxide is off the charts.

 

I've been told that the fuel mixture is too rich.

 

 

Anyone have ideas or solutions?

[LenRobertson]

I'll assume you checked the fuel level in the float bowl by looking through the round window on the front of the bowl. If the float isn't adjusted to give the correct fuel level in the bowl, that could flood the carb.

 

Take the air cleaner off and look down the carb throats. If this is a Cali smog carb, the small venturi (round ring thingy) will be supported by a tapered bar across the throat. Grab onto this bar with your fingers or needle nose pliers and make sure there isn't ANY movement in any direction of the bar/venturi unit. On one end of this bar there is an O-ring between it and the carb body. If this O-ring is bad or the bar is loose so the O-ring doesn't seal, it may cause gas to be sucked down the carb throat.

 

When I got my F10, this bar/venturi had come completely loose from the carb body and was keeping the choke butterfly from opening more than a little bit. Now that was running rich!

 

Len

[datzenmike]

CO is incomplete combustion... not necessarily over rich. Assuming the carb jetting is stock and correct, other causes of poor combustion can be...

 

Thermostat stuck open and engine running too cold. Engines are designed to run just below 200F for best economy and lowest pollution.

Bad ignition. Fouled plugs, bad wiring, cap or rotor.

Choke stuck on or part on.

Carb flooding.

Extremely dirty air filter

Fuel level too high or low. Should be in the middle.. very important.

If at idle, mixture set incorrectly.

Failed catalytic converter.

[racerx]

Did you try adjusting the carb?  How old is the carb?  Maybe needs a rebuilt.

[DanielC]

Is the high CO at idle, or a part throttle run?

Try to give as many details as you can about the test conditions it failed at. That will help with long distance computer diagnosing. 

Emission problems are hard enough with the car in your shop, and a bunch of test equipment.

[john510]

Hi Everyone,

 

I failed my biannual smog test because my rebuilt Hitachi Carburetor is running too high CO's, which means too much fuel is getting through.  The carburetor is running too rich.  HydroCarbons are low.  Nitrogen Oxides are low.  The Carbon Monoxide is off the charts.

 

I've been told that the fuel mixture is too rich.

 

 

Anyone have ideas or solutions?

Did your smog guy tell you its running rich ? don't trust them for an accurate assessment.Tune it up first.Does it have a catalytic converter ? if so it may be done.

[Nicholas7620]

The smog test is done at 15mph and 25mph.  I was able to adjust the newly rebuilt carb to .1 PPM at idle.

 

At 15mph I think the reading was 6.8?  and at 25mph I think the reading was 10.60.  I'm at work and I have to go home upload the smog test printout.  I have the day off tomorrow. 

 

I'm wishing I had an exhaust gas analyzer.  The smog shop let me adjust the idle on the carb CO reading to .1 before booting me out.

 

Thanks for the ideas everyone.

[DanielC]

High CO is way too rich.  There is carbon in gasoline, and when carbon combines with enough oxygen, it makes CO2.  If there is a lot of CO, and not CO2, there is too much fuel.

 

A good tune up may help.  Adjust valves.  Set timing, 

 

Make sure the float level is correct.   At 15 MPH, the idle circuit in the carb probably has a good influence on the fuel air mixture.   At 25 MPH, the idle circuit has a lot less influence.

 

A vacuum gauge will help you a lot when setting the idle mixture on a hot engine.   You will also need a Dwell-Tachometer that will read low RPMS.

 

Adjust idle speed to factory recommendation with the idle speed screw.  Hook up the vacuum gauge.  Adjust the idle mixture screw to the highest vacuum.  If the idle speed goes up, adjust idle speed screw back down to the recommended RPM.  Adjust the idle mixture some more, to highest

vacuum.  After each change, wait about 10 seconds for the change to take effect.

Once you have found the highest vacuum, at the factory recommended idle speed, turn the idle mixture (yes, I do mixture) in to drop the idle RPM about 50 RPM.

[Nicholas7620]

Here is my Smog Test Result.

 

[Nicholas7620]

DatsunMike

 

CO is incomplete combustion... not necessarily over rich. Assuming the carb jetting is stock and correct, other causes of poor combustion can be...

 

Thermostat stuck open and engine running too cold. Engines are designed to run just below 200F for best economy and lowest pollution.

Bad ignition. Fouled plugs, bad wiring, cap or rotor.

Choke stuck on or part on.

Carb flooding.

Extremely dirty air filter

Fuel level too high or low. Should be in the middle.. very important.

If at idle, mixture set incorrectly.

Failed catalytic converter.

 

I agree.  CO readings are too high at 15 mph and 25 mph to pass smog test.

 

The thermostat is stock, engine run at 180 degrees.

 

I installed new plugs, rotor, cap, new air filter.

 

I agree the fuel mixture is not right.

 

The catalytic converter is good.

 

Today is my day off.  I'll try to get the CO reading down.

[Nicholas7620]

I'll assume you checked the fuel level in the float bowl by looking through the round window on the front of the bowl. If the float isn't adjusted to give the correct fuel level in the bowl, that could flood the carb.

 

Take the air cleaner off and look down the carb throats. If this is a Cali smog carb, the small venturi (round ring thingy) will be supported by a tapered bar across the throat. Grab onto this bar with your fingers or needle nose pliers and make sure there isn't ANY movement in any direction of the bar/venturi unit. On one end of this bar there is an O-ring between it and the carb body. If this O-ring is bad or the bar is loose so the O-ring doesn't seal, it may cause gas to be sucked down the carb throat.

 

When I got my F10, this bar/venturi had come completely loose from the carb body and was keeping the choke butterfly from opening more than a little bit. Now that was running rich!

 

Len

 

Here is a picture of the round window.  You can almost see the fuel level at a little less than half.

 

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This picture is the cross bar, flap.  Some people call it a butterfly.  When cold the flap is in a vertical position.

 

[Nicholas7620]

Here is a my problem.  When I start my COLD B210 engine the choke closes the flap like this.  The engine sputters and gags.  I have to run out an open the flap and stick a metal rod down the throat to keep the flap open or hold the flap verticle with my fingers. 

 

[datzenmike]

Normal when cold. It should open fully in 5-10 min depending on outside air temperature.

 

Should look like this when warmed up...

 

[Nicholas7620]

I have to hold or prop open the butterfly/flap until the engine warms up to the point I can accelerate off the choke and then the engine idles good.

 

 

 

 

 

Maybe this is causing my engine to run rich at 2000 rpm and 3000 rpm on the smog check.

[Nicholas7620]

Normal when cold. It should open fully in 5-10 min depending on outside air temperature.

 

Should look like this when warmed up...

 

 

Mike it run like crap when the flap is closed, smells like unburned fuel and the engine won't rev up to normal speed, or idle fast with the flap closed.  The engine will fast idle when the flap is propped open or held open with my fingers.  Engine won't run good with flap closed.

[LenRobertson]

It sounds to me like your choke isn't adjusted correctly; that it is holding the choke butterfly on too hard and/or for too long a time. The way to adjust this is loosen (don't remove) the three screws that hold the plastic choke spring cover and SLIGHTLY rotate the cover so you can feel less spring pressure pushing the choke butterfly closed. There shouldn't be much spring pressure, just enough to close the butterfly when the engine is cold. I suppose this time of year in Cali you don't need much spring pressure. There is always a chance someone has installed the plastic cover wrong and it will need to be removed and reset. But only worry about this if you can't lessen the spring pressure by rotating the plastic cover.

 

Another thing to check is that you have 12 volt power at the terminal on the choke spring cover with the engine running (not just with the key on). This power is what heats the choke spring and lets the spring gradually release pressure on the butterfly. This 12V power come from the alternator circuit and only when the alt is turning, hence the running engine.

 

Len

 

 

[datzenmike]

Agreed, may be too much choke for the outside temperatures. Set this when engine is cold. I turn the loosened choke till it just closes and try several cold starts. It should start after one pump of the gas to set the choke on and rev smoothly to a fast idle1,800-2,200 rpms. Often I have to slightly adjust richer so the fast idle stays on slightly longer. If the choke come off too soon, about the third stop the engine falters.

 

A warm engine evaporates all the fuel in the cylinders and runs well. A cold engine lacks power because the gas doesn't fully evaporate because the carb intake, head ports, valves, combustion chamber and pistons are not yet up to running temperature. Running extra rich during this time assures that more of the fuel evaporates and a fast idle speeds the warm up. EFI cars can more closely tailor the fuel mix and engine RPMs and barely have a 'fast idle'.

[Nicholas7620]

ok, I'll try adjusting choke.  I won't know what my CO readings are at 2000 and 3000 rpm.  Len  had a good point  when he observed it's so warm in CALI, I don't need any choke.  I'm thinking I could experiment and unplug the choke.

 

 

i do hear soft backfires when I rev past 2000 rpm and shift to the next gear.  Then when I rev up to 3000 and shift to the next higher gear I hear more, higher pitched back fires. i'm not sure why, but I'm guessing my fuel mixture is too high.

[Roadster-ka]

Don't unplug the choke. Power is needed to open it.

[datzenmike]

ok, I'll try adjusting choke.  I won't know what my CO readings are at 2000 and 3000 rpm.  Len  had a good point  when he observed it's so warm in CALI, I don't need any choke.  I'm thinking I could experiment and unplug the choke.

 

 

i do hear soft backfires when I rev past 2000 rpm and shift to the next gear.  Then when I rev up to 3000 and shift to the next higher gear I hear more, higher pitched back fires. i'm not sure why, but I'm guessing my fuel mixture is too high.

 

Normal. During shifts the carb closes and only a small amount of fuel enters, enough for idle for idle... but the engine is revved up anywhere above 2,000 RPMs and the mixture will go very lean and miss fire.

[Nicholas7620]

Ok, scrap the unplug choke idea. 

 

I talked to the smog tech and tomorrow he will let me try to adjust CO carb mixture at 2000 rpms and 3000 RPM CO rpms readings.  I'm basically getting to use an expensive "sniffer" to see if the newly rebuilt carb can be adjusted to less than 1.52% and I'm at 11.26%, (yikes that's bad) at 2000 rpm  and adjusted to less than 1.32% at 3000 rpm and I'm at 6.8%, thats bad too.

 

I'm renting the sniffer for a smog fee.

 

Hopefully tomorrow the carb fuel mixture can be adjusted to lower CO emission to 1% or less.  

[datzenmike]

I can't think of any way to adjust a carb like you're saying. If the choke is off you can't turn it more off. The primary jet sets the mixture ratio and only way to change it is take apart and change the jet.  The idle mixture can be adjusted but this only affects up to about 1,000-1,200 RPMs.

[Nicholas7620]

I'm probably wasting my time then, but I'll put in another new set of plugs in hope for the best before I take my Datsun to a smog repair shop.

 

In the back of my mind I wonder if my smog pump is blowing air like before.  I have a rebuilt one I can swap in. 

[datzenmike]

Well the pump adds air to the exhaust so it will burn completely. You could try it. But keep in mind it only cleans up what little extra gas isn't burned in normal combustion. It can't fix a major problem

[DanielC]

Check to make sure the choke is fully open when the engine is warm.  Run the car for about ten minutes, and set the hand brake, and with the transmission in neutral, take the top of the air cleaner off.  The choke plate should be fully open, vertical.