Carbureted subaru emissions, high CO @ 2500 fail

Emissions test is fine at idle, fine HC at 2500 but high CO at 2500. The question: Can this be the catalytic converter? I would think a bad cat would also let too much HC past.

My bigger issue is I am trying to decide between just getting a new (remanufactured) carburetor (any suggestions for good carb remanufacturers?) or replacing the catalytic converter. I like the vehicle, know its history and want to keep it etc, also a carb or cat, while pricey, is still less expensive and fuss than another vehicle.

Some background: I’ve done lots of stuff to the vehicle (1986 Subaru GL 4-door sedan on-demand 4wd which I love 1.8L SOHC Hitachi carburetor on an EA-82 engine) in my efforts to get it passed - changed plugs, wires, cap and rotor, replaced a bunch of vacuum tubes (and there are many), pulled the carb apart and cleaned the passages with air and cleaned the jets in carb cleaner (but no formal rebuild kit this time but did that 2 years ago), adjusted the float level (float is not sunken either) so tight it just starts to lean surge under heavy load, adjusted the timing using vacuum, tensioned the timing belt idlers, did compression check (which gave 145 148 150 160), chanted, prayed, begged, etc.

Any thoughts (well almost any) would be welcome.

Thanks and hi from Fairbanks AK,

Dave A.

You’re asking for a lot from those Subaru Hitachi carburetors. They were near junk when new and degraded from there. Very problematic carburetors to put it midly.

There are several things that could be behind this. A partially clogged catalytic converter can do it and this could be verified with careful use of a vacuum gauge. Sometimes the effect on the gauge can be very subtle so one has to really know what to look for.

I hope none of those tubes you mention replacing (which I assume to be various emulsion tubes and air bleeds) were crossed up. One out of place can become a nightmare.

The next area is a very common site for problems. Note the attached eBay auction. Note the fiber block between the lower throttle body housing and the float chamber housing.

These 2 sections of the carburetor are prone to warping; especially the float chamber housing. When warped, gasoline and air leaks can develop and the effects can be mild to severe in nature.
Whenever these carbs are disassembled a fairly heavy file should be run across the faces of both the throttle body and the float chamber housing.
As you rake a file across there you will see what I mean; especially with the float chamber housing. I’ve seen these things warped .030 of an inch in severe cases and that’s astronomical for such a short stiff length of alloy.

I can’t recommend a carb rebuilder because one would be surprised at the number of qualified Subaru techs or dealers who do not know of this problem much less an aftermarket rebuilder.

One of my old Subarus was inflicted with one of these things and after the last straw I made an adapter and mounted a one-barrel carb off of an old Ford 200 CI 6 cylinder. Best thing I ever did and carb problems ceased immediately. With emissions testing this would likely be a no-go in your area but it made a world of difference on mine.
Hope some of that helps.

(And the timing was set as per the instructions on the hood I hope)

You failed because the engine is running “rich” at 2500 rpm. Too much gas. You might try cleaning the entire PVC system, not just the valve. The carb will have a power circuit that enriches the mixture for acceleration. If it’s stuck in the “rich” mode, you will fail the test because of CO. Some carbs use metering rods which are withdrawn from the main jets, thus allowing more fuel to flow and some bypass the main jets with a rubber diaphragm controlled enrichment valve. Vacuum holds the valve closed against a spring. If the diaphragm ruptures, the spring is free to hold the valve in the open position. There may be an external cover over this valve.

These cars ('81-87 models with carburetors) are emissions nightmares because of problems like yours. Some used an electronic “feedback” carburetor that replaced the metering systems described above with a “mixture control solenoid” which constantly adjusted (theoretically) from commands given by the ECM, which gathered information from the oxygen sensor. If your carb has an electrical connector, it is one of THOSE and good luck.

I can’t believe Alaska requires emissions testing…Palin will be back in a couple of weeks, you should put her to work on that. There is no reason for emissions testing in Alaska (or anywhere else)…

High CO is the one I have no personal experience with. I could agree with too much fuel but it’s a guess for me. Check the vacuum advance to see if it is working, not just if it holds vacuum. You have to take the distributor cap off and make sure that the plate is rotating. Some of them jam in place or the vacuum advance is just permanently stuck. They’re cheap to replace. The EGR valve is supposed to lower oxides of nitrogen but you might want to check it too. Some of the basic ones can be checked by applying vacuum at idle and seeing if the engine stalls or at least runs roughly. If it doesn’t, the valve is shot. Some aren’t so easy to check.

Perhaps the O2 sensor is bad.

Thanks for this, ok4450. I have to admit I was a little surprised (dismayed) to narrow problems back down to the carb. 2 years ago this cropped up and I did a rebuild with a NAPA kit plus a new float and all and it got it okay that time. Your comments on the warping are interesting; I did not know they were prone to that. I had probed for vacuum leaks with propane; do you think the leaks you describe be enough to respond to the propane?

I have another question - how would you test for a partially clogged cat using vacuum as you describe? I’m not familiar with that procedure.

Timing - the hood sticker is gone so I initially went with the Hayes (or Chilton I forget) 8degrees BTDC. A friend who has worked a lot on these said when the engines are this old the tolerances are a little sloppy and he prefers to do timing using a vaccum gauge - rotate distributor until vacuum maxes out then back off an inch of Hg.

Just for info, the vacuum being pulled at idle is 18 with an infrequent hiccup - not a miss, judging by today’s emission test that showed ~250 HC at idle (limit is 750 here), but the idle still isn’t as clean as it should be - should be steady with a healthier vacuum, say 19, I would think. 18 seems too low. It has led me to wonder if I have missed a small vacuum leak; what you described about warped carb surfaces makes me wonder about that.

Thanks again for taking the time to post.
Dave A.

Thanks for your response, Caddyman. I did check the PCV valve itself - works okay - but didn’t give the rest of the PCV system a good shakedown. I had actually been wondering about the power circuit as well. I can’t see a way to access that on this carb (and I’m also not really sure to what extent it has one, but most carbs do sot it probably does) which is why I was thinking about a factory rebuild on the assumption they get to that (maybe I’m wrong?? - although presumably they test them, but probably on a bench and to what extent who knows I suppose - I have no experience with reman carbs). Luckily, it isn’t an electronic feedback carb. I can’t see anything in the bits on NAPA or Royzone do-it-yourself rebuilds that addresses the power valve, again leading me to the factory rebuild.

Fairbanks is interesting - I was also very surprised to come here and find an IM program like we’re L.A. or something. We have 50,000 people here and are ~140 miles below the arctic circle; essentially the end of the road in North America. The deal with the emissions is the winter when it gets dark - the lack of sun means the ground gets very cold - we can hit -55 without a problem - and cold, dense air drains into the valleys, i.e. Fairbanks. We end up with what they call an inversion - it gets warmer as you go up into the atmosphere. This is very stable and traps anything emitted by a wood stove or car right near the ground. We also have almost no wind throughout the winter. So - Fairbanks ended up hugely out of compliance with EPA on CO and particulates (soot) and they were going to sue the city etc if they didn’t implement this program. So - here we are. They are actually thinking of getting rid of it in fact because we’ve gotten so much cleaner. Everyone leaves their cars running here anyways - go see a movie and the lot is full of cars (mostly big pickups) all running. I think cracking down on that would make more of a difference. Summer is no problem (except for forest fires and hornets).

Thanks pleasedodgevan for replying. Could the vacuum advance be checked with the timing light? I replaced the cap and rotor so hopefully they are okay. I did in fact renew the vacuum hose to the distributor, wondering like you if it might be a weak advance issue. By plate do you mean the flat rotor or something else?

I would think it would really start pinging if advance was weak, but maybe if it’s subtle enough it would just richen the mixture without getting into pinging (actually pinging is a lean symptom isn’t it so I suppose it wouldn’t ping with weak advance)

Thanks again for replying
Dave A.

Thanks Cougar. I don’t think this vehicle has one, although I could easily be mistaken. It’s feedback systems are pretty primitive, limited to mostly mechanical linkages and vacuum hoses. I can see why carbs have disappeared from cars…

Oh, I did check the EGR valve. It’s not to hard to get at - I pulled it off, verified with my hand vac pump that its diaphram pulled the valve open and that it stayed open with vacuum applied. Cleaned some crud out but nothing too terrible. Small black crystals, actually, which combined with what the spark plugs looked like verified for me the rich condition at cruise.
Dave A.

Oh and I’m hoping none of the hoses are crossed… You’re correct; they are what I see as after-thought emissions controls stuck onto an engine not originally designed for it. There are six tubes that go to the carb alone, not counting fuel feed and return! I tagged them all as I did it, although one never knows.

Thanks for the ebay link too.

Another thought on the float - I was also surprised to be getting just the first hint of lean surge while hauling up a steep hill (at almost wide open throttle) and yet getting a rich condition at 2500 rpm! Someone else I talked to said adjusting the float is not very productive for just the reason I observed - he said it’s fine if the fuel level is too high - the jet/metering takes care of the flow - but it will lean the engine out if its too low.

To clear up the ignition timing thing first, the proper timing should be 8 degrees +/- 2 degrees. When working for Subaru we preferred a 10 degree setting if possible with vacuum advance hoses plugged.
A word of warning here. You should NOT set the timing by vacuum as it is possible to destroy an engine by burning some pistons out. (seen it several times)

The warped carb sections are a very common and depending, it may not be noticeable externally. It can leak around that fiber insulator block internally. I’ll put it this way; after discovering this trait many years ago I’ve never seen one that was NOT warped. The only difference was the degree. Gasoline can get pulled past that insulator into the manifold.

If you tear into the carb to file it down be sure to lay the file completely flat on the surface and use slow steady strokes to avoid rounding off edges etc. After about 2 or 3 passes you’ll see what I mean. Most of the warpage will be on the float chamber section but sometimes the cast iron throttle body warps excessively also.

As to surging here’s something to consider. I discovered this way back when while working for a Subaru dealer when this problem first started. Your car should have 2 fuel filters on it. One should be in the rear underneath by the driver’s side rear wheel. The other filter should be under the hood near the driver’s windshield pillar.

This “filter” underneath the hood is not technically considered a fuel filter by Subaru; they consider it a vapor separator to aid in preventing vapor lock. Vapor lock was a chronic pain in the neck on these cars; especially during warm weather.

What I discovered way back when is that the vapor separator (which you may note has 3 nipples and is mounted upside down) actually has the direction of flow reversed. The cars came from the factory this way and while Subaru claims this does not hurt anything I strongly disagree with that argument as I’ve solved many surging problems by reversing 2 of the hoses.

If you examine this vapor separator you should see it marked with arrows for direction of flow. It will flow more one way than it will the other.

As to manifold vacuum I don’t see anything wrong with 18" if it’s rock steady at idle.
If you perform a test with a vacuum gauge here is the way to detect a blockage in the converter. With the gauge connected to manifold vacuum blip the throttle quickly. The needle should drop instantly to zero. Close the throttle quickly. If it returns instantly to 18" you’re fine converter-wise. If it returns slowly, OR if it returns to a number slightly larger than normal before dropping back then the converter could be partially clogged. (Say returning to 19 or 20 before settling back to 18")

I would point out that your car does use a computer controlled carburetor with an O2 sensor. The ECM is underneath the steering column, controls several carburetor air bleeds, and codes are read by following a certain procedure (check a manual for that) and watching the LED flashes on the ECM.

You should set the float level where it is even with the dot on the sight glass. Also make sure when the vehicle is idling (and with the air cleaner top off) that you do NOT see fuel dribbling from a discharge tube down the throat of the carburetor. If so, the throttle plate is opened too much in an attempt to cure another problem.
And be SURE to check that vapor separator I mentioned as these cars are prone to surging/bucking/jerking due to any restriction at all in their fuel filters or vapor separators.

Pardon the length of the post; just trying to cover a number of bases in one shot and hope it helps.

No need to apologize for the length - these are great pointers.

Manifold vacuum is mostly steady at idle but has intermittent, non-regular drops of around 1" (drops every second or two, which you can hear in the rpms anyways without the vacuum gauge). I’m checking vacuum using the tube that runs back to the firewall (the one that is controlling the heater setting buttons on the dash - I am assuming that is its destination) - is there a preferred tube to pull for checking vacuum or is that one okay? Also, when I pull the vacuum tube the engine does not change - maybe increases the rate it drops by a little bit. I’ve heard that if there are absolutely no leaks anywhere that pulling a hose will cause it to run rough, and if it’s running rich at idle pulling a hose will cause rpms to increase.

I’ll check some of these things out and get back to you. Oh do you have any thoughts on the possibility of a power valve being bad in this carb, as another poster (caddyman) above suggested. This is something I’ve seen elsewhere as a possibility.

Thanks again for the help. It makes me wonder how many carbs have been replaced as “bad” that just require some squaring up with a file.

Dave A.

Just did the cat convertor check - vacuum starts at 18, a flick of the throttle cable drops it to zero and upon release it comes back quickly to 20 then settles back down to 18. Sounds like the convertor is worth a closer look…
Thanks for the pointer.

A CO failure like yours is almost ALWAYS related to a carb problem. Are there any electrical plugs connected to the carb, other than the choke?

You can game the test by installing a “Y” fitting in the PVC line and installing a second PCV valve in the second leg of the “Y”, one intended for a V8 engine. Just let this second valve suck air for the test. Your CO readings will be considerably lower.

OK4450 or others,

I read your comment about using a vacuum gauge and checking for a partially blocked CAT. You stated that the vacuum reading will go higher when the throttle is closed and then settle back a couple inches if the CAT is partially blocked, say from 20 back to 18. This seems backwards to me and I would think that the pressure should go from a lower to a higher reading when the throttle is closed and the vacuum would increase. Can you tell what am I missing here?

There are two plugs on the carb - one with two prongs, one with three prongs. I don’t know at this point where they go/what they do. I can check into that further in Chilton/Hayes when I get home. I got my hands on a high temp thermometer here at work and will check the temperatures on the cat, front and back. Although, now I think about it, all that will probably do is confirm that the cat is working hard on the excessive CO issue…

Your comment about high CO being almost certainly carb is something I had been wondering about - I would have thought that a cat converter going bad would allow HC to get high as well. Instead HC is nowhere near limit while CO is nowhere near passing (4% when limit is 1%).

It may seem backwards but with a minor clog it is quite possible that the vac. gauge reading will revert to a slightly higher than normal reading when the throttle has been snapped closed.

An example could be my SAAB just a few weeks ago. While doing some maintenance work I threw the vac. gauge on it just for a quick check even though the car was running fine. At idle it had a shade under 17" of vaccum at idle. When the throttle was blipped closed the needle would jump to 18 for a second or so before dropping back to the normal 17. Since the converter is pretty easy to remove on these cars I yanked it off and knocked the substrate out of it. It was about 35% clogged based on examination of the honeycomb. No big deal since I have a stash of extra parts.

OP, the wire connectors on your carburetor are related to things like the anti-diesel solenoid and the electric choke. JMHO here, but I don’t think the problem is related to the power valve. The power valves on these carbs are about as bulletproof as you can get. I’ve never seen a bad one although I have seen inoperative ones due to vacuum leaks and/or carburetor warping (the power valve receives its vacuum through one of those 3 tiny holes in the insulator block).

It’s entirely possible that carbs have been replaced because of the warping problem because as I mentioned; few seem to be aware of it.
I got into a tiff with a service manager at a large dealership I went to work for because of this. I’d been there for a few months and this problem reared its head once again on someone’s car. He started being a smartaxx telling me that “Subaru never had a carb problem until you went to work here”. Sorry dude, I don’t build them, just fix them.
He insisted on seeing this problem when it was torn apart so I obliged him after making 2 swipes over it with a file. He took one look and said that’s not a big deal; give me the file. Five minutes later he had not smoothed it out yet, was sweating like a pig, and mumbled “go ahead and fix it” as he stalked off. Thank God for for his ex who caught him a month later with one of the office help after hours, filed for a divorce, and his hiney got canned like a tuna by both the ex and the employer.

There is another somewhat common problem that can mimic a lean surge and that is a worn distributor shaft. It’s also fairly common on these cars. Remove the cap/rotor and note if you can wiggle the dist. shaft sideways. A couple of thousandths is acceptable but anything over that is not.
There are a few other things in the carburetion and carubetion control system that could cause this but to test all of these you would need a factory service manual. This includes that assortment of thermovalves, etc. Heck, even the secondaries on the carburetor have an electronic timer that will not allow them to operate for 241 seconds; and no, I don’t know why this particular time frame was used.

Bottom line is you have to hit the basics first before wading into the other. Hope this helps some more. :slight_smile:

The reply for VACUUM ADVANCE. The rotor won’t move, it’s the plate that the pickup is on. You will see either the link from the vacuum advance if it is on top of the plate or the pin sticking up from under it. You can check it with your vacuum tester. Most carbureted cars had a vacuum advance. You will see something move if it works. You can use the timing light along with the vacuum pump with the engine idling. You can even remove the vacuum advance from the distributor and see if it moves freely. I gained four miles per gallon by replacing the vacuum advance on my 87 Mazda truck; some power too. 49 HP to 52 HP. I hope you don’t have ignition points on that thing. If there is a plastic cover under the rotor, you might want to lift it and look. I bet you don’t.