Failed CA Smog Test - High CO Reading

[Eric_S]

I have had my 78 FJ40 registered as NON-OP for a few years since I have always had such a difficult time passing the CA Emissions Smog testing on the dyno. Well, today I decided to take it down the the test only station and see what the numbers are before I try to change anything.

Here is a little background info....

12/78 FJ40 CA emissions, stock 2F, Downey CARB header, SM420, 5.13 gears, 38.5 SXs
Fairly new cap/rotor/plugs/wires, spark plugs gapped at 1mm
Fresh engine oil/filter change
Carb bowl just below 1/2 way in the window
Idle set at 700 RPM
Idle mix screw is 5 turns out
1/2 tank of fresh gasoline
Vacuum gauge reads 16-18" at idle (bounces fast between numbers)
Vacuum gauge reads 19" steady at 1000RPM, and 20" steady at 2000RPM
Compression: 145, 140, 142, 135, 140, 135 (dry)

Location is San Martin, CA ~ sea level

15/25 MPH tests were done in 3rd gear since it was too high of an RPM in second gear for the 15mph test.

......................%CO2...%O2........HC (PPM)
TEST......RPM.....MEAS...MEAS......MAX....GP....MEAS
15 mph...1330.....11.8....2.3........196.....386....95
25 mph...2065.....12.6....0.8........161.....336....50

.......................CO (%)..........................NO (PPM)
TEST......RPM....MAX....GP.....MEAS.........MAX....GP......MEAS
15 mph...1330...1.59...3.09....2.98.........1507....2753....418
25 mph...2065...1.39...2.89....3.42.........1367....2553....273

MAX = maximum allowed
GP = gross polluter limit
MEAS = actual measured reading

HC look good, NOx look good, but.....

I failed the 15 MPH test with a CO reading of 2.98 = FAIL
I failed the 25 MPH test with a CO reading of 3.42 = GROSS POLLUTER


What kind of things can I do to lean out the carb to reduce CO since it is running very rich?

 

[HKforte]

High CO is caused by incomplete combustion. The mixture is probably rich. Does your carb have a power valve? Make sure the power valve port on your carb has manifold vacuum going to it. The mixture screws on your carb have nothing to do with this issue, since at 15 our 25 MPH we are outside of the idle circuit.

I had this same issue, and I did two things. I replaced a gasket within my carb that was leaking and I also made sure that my power valve was functioning properly. After making those two changes I was able to pass smog.

 

[Bill McC]

I would leave California immediately. They won't be happy until you crush your landcruiser, walk to work, and pay 99% of your income to help the children and maintain "critical services" of the state.

May I suggest a non-CARB state? Perhaps FLA or Nevada?

 

[HKforte]

I noticed that you mentioned the following:

Vacuum gauge reads 16-18" at idle (bounces fast between numbers)
Vacuum gauge reads 19" steady at 1000RPM, and 20" steady at 2000RPM

Your vacuum reading should not be jumping up and down that much at idle (600 to 700 rpm). The high RPM contributing to a steady vacuum reading is only masking the problem. You may have vacuum leaks.

I would check your valve clearances and also check your intake manifold, carburator, and intake vacuum ports for any leakage. If any vacuum hoses are leaking, replace them.

What is your timing set at?

 

[Eric_S]

I took the top of the carb off and checked the jet sizes. Primary = 1.24 and secondary = 1.71 which is what SOR lists as factory sizes.

 

[Pin_Head]

X2 on the power valve not operating/stuck open.

 

[numby]

High CO is caused by incomplete combustion. The mixture is probably rich.

A lean miss can give a high CO reading as well IIRC.

 

[Pin_Head]

A lean miss will cause unburned hydrocarbon (HC) to go up. CO is incomplete oxidation due to excess carbon over oxygen (eg rich mixture).

 

[Eric_S]

Power Valve - This is only active when the engine is cold or when the engine is hot AND the throttle position switch is pressed. Otherwise, it should have manifold vacuum on it pulling the power valve plunger up releasing the lower spring loaded plunger sealing off the float bowl from bypassing the main jet. This should be the case when my Cruiser was on the dyno.....power valve disabled.

I will go out and check the power valve. I do not have a thermo sensor in the head for the power valve. The connector is hanging so the power valve should not be active when the engine is cold since the sensor should be shorted to ground. As the coolant heats up, the sensor should open and disable the power valve (unless the throttle position switch is pressed).

 

[HKforte]

From what I understand on the '78 carburetor, the power valve is not regulated by heat, it is regulated by vacuum only. Whether hot or cold, your vehicle has full vacuum at idle and should be pulling on the power valve port on your carb and preventing the power valve from opening. The power valve will open when your have your foot on the throttle all the way or almost all the way, creating a condition where manifold vacuum is zero or close to zero.

If you do not have manifold vacuum connected to your power valve, then you will be running rich all the time. You can also remove your power valve and test it manually to see if it's functioning properly. I have a spare one, in case yours is bad.

 

[Eric_S]

I took the top of the carb off again and here is what I discovered. I measured the power valve piston and it protrudes 25mm from the carb surface. When I apply vacuum, it sucks up 2mm and protrudes 23mm from the carb surface. Then I measured down from the top of the carb (w/o gasket) to the top of the power valve and it was 25.4mm down. So, there is no way the power valve piston could ever activate the power vavle since it doesn't even touch it.

So if the power valve is leaking causing a rich condition, then there must be enough vacuum when the throttle is opened up to overcome the spring on the power valve. I took the power valve out and applied vacuum to the bottom jet (070) and it would leak a little. So I took an M8 socket head cap screw and put a sealing gasket on it and threaded it into the power valve location. This should block all fuel flow.

 

[Eric_S]

So I took the carb apart and removed if from the engine, I cleaned out all of the passages and put it back together. This time I noticed the power valve piston retainer was installed wrong. There was a little tab that had a 90* bend in it. Before this was pushing the power valve piston into the bore more so the power valve piston would never touch the power valve. Anyway, I installed it correctly so the power valve piston was now flush with the top of the carb and sticks out about 28mm insteand of the 25mm before.

I lowered the float to a little under 6mm, and the fuel was just below the bottom of the window. The factory spec says 7.5mm and when I set the float to this, I could not see any fuel in the window. Maybe the needle and seat are bad????

So, I decided to totally block off the power valve by installing an M8x10mm socket head cap screw instead of the power valve. This was just to make sure the power valve was not leaking. I headed down to the smog station again and the results were better, but still way too rich.....

%CO dropped from 3.09 to 2.45 @ 15MPH and from 3.42 to 2.76 @ 25MPH


HC was similar, CO went down some, NOx went up a little. At least I am not a gross polluter anymore.

......................%CO2...%O2........HC (PPM)
TEST......RPM.....MEAS...MEAS......MAX...AVE....MEAS
15 mph...1306.....11.8....2.6........196......52......101
25 mph...2037.....12.8....0.9........161......44......46

.......................CO (%)..........................NO (PPM)
TEST......RPM....MAX.....AVE.....MEAS........MAX.....AVE....MEAS
15 mph...1306...1.59....0.24.....2.45.........1507.....553.....592
25 mph...2037...1.39....0.21.....2.76.........1367.....474.....355


What else can be causing the high CO?

Could it be the dyno, large tires, 3rd gear in the SM420 are putting too much load on the engine and requiring way too much fuel to keep up the 15 and 25 MPH? Leaking valves or seals?

Maybe I just need to install a smaller main jet in the primary? I currently have a 1.24 in there.

 

[Fast Eddy]

This is just my opinion, but...

Send the carb down to Marks Off Road. For a bit over $300, it will come back new and able to pass smog. I have stock jets in mine and it passes fine.

While it's down there, do a compression check. If it's not great, pull the head and get a valve job done.

Did you at least adjust the valves before you took it in for the test?

I worry that you're hacking the power valve closed and may not have all the VSVs, gas valve, HIC, and other magic. Do you have the smog manual? I do.

There are a bunch of good threads on getting a '78 to pass, like this:

https://forum.ih8mud.com/40-55-series-tech/226005-vsv-part-78-fj40.html

 

[Eric_S]

Does anyone know of a reputable place to get a valve job done in Calif (San Jose area)?

 

[Pin_Head]

So it is not the power valve stuck. There are other possibilities:
1. It may not be getting enough air, so a clogged air filter or partially applied choke, or anything obstructing air flow could cause high CO.
2. On the fuel side, any clogged air port inside the carb, like on the slow jet or emulsion tube could cause high CO. Since these are tiny holes, you need to verify that they are open.

Since HC is low, it is not a misfire or bad compression problem. You could try a smaller primary main jet to get it to pass, but this may be more of a band aid than a cure. Do a complete tune up and check the air side first.

 

[Eric_S]

Air filter is clean and the hot air intake flaper is open during the test. Maybe I just need to route the air cleaner inlet to a better spot? Right now it is in the stock location

The choke was unhooked and the plate was vertical.

I sprayed both of the slow jets with carb cleaner and compressed air. They looked clean all the way down when I was done.

I sprayed the emulsion tubes also, but I could not visually check them like I could the slow jets.

 

[Pin_Head]

Presumably, your cruiser used to pass, so something is wrong now that is providing too much fuel. In situations like this, I just do a complete rebuild, cleaning everything with carb dip (spray doesn't cut it, and you can't get carb dip in CARB restricted areas) and verifying that all the tiny holes are clear by running a nylon monofilament line throught them. Sometimes, it takes less time to rebuild it properly than to find out what is wrong. Your initial idle mix setting (5 turns out) seems rich to me by about 2 turns. This usually has a minimal effect on the mixture above idle, but you are at the edge of failing and every little bit helps. You should tune it by the lean drop method in the FSM. You should fix the power valve as it helps going up hills.

 

[Eric_S]

Can anything in the head cause it to run rich (ie valves, valve seals, etc)? My vacuum gauge flickers really fast between 16" and 18"

I really can't get a good feel trying to do the lean drop since my vacuum gauge bounces and is not steady at idle. It is hard to tell when I have reached max RPM. I am afraid that when I set the idle mix screw to say 2-3 turns out, I am having to turn the idle speed screw too much causing the throttle plate to open too much which may start to pull fuel from the nozzle.

I may just send the carb out to one of the PROs here on mud to have a look at since who knows what has been to it since '78.