Emission - FAILED!

[abnovak]

Well, I failed emission today (Denver, CO). Just put a new - not rebuilt but factory original - ZS Carb on it too. Got it directly from Joe Curto who I am told is a very trusted carb source. I am confirming but it was supposed to have a high altitude needle installed prior to shipment.

Here are my readings: RPM 2500 Idle Limit
HC PPM 264.5 932.2 400
CO% 5.72 7.10 2.0

Looks like I am running very rich. Would the high alt needle help or hurt that? I pulled the vaccum advance and plugged it - no change to idle. Shouldn't that have some impact? Pulled the air pump hose and plugged it - no change to idle - the manual says there shouldn't.

After it heats up (15 min and/or about 10 miles), the idle drops off down to about 800 and a little rough. I give it a little gas and it goes back up, idles at 1000 and is smooth. Wait a bit, and it does it again. Has a brand new water choke on it.

Funny thing too and probably is a diff problem, but when I turn on the lights, I lose about 300 RPMs - goes back after I turn them off. Never had that happen before.

Carbs arent my thing (mental block I am in therapy for) but I think I need to lean the mixture through the Fast Idle CO Adj first then tackle the needle if necessary. I have the tool but am reluctant to dive in. When I did adj the Fast Idel CO screw, counter clockwise one full turn, didnt seem to have any effect. There is a white plastic cover surrounding the adj screw but I can access the screw and turn it. Do I need to take that off or do something with it? My last ZS didnt have that on it.

Any suggestions or tricks? Once I get it licensed, as long as its classifed as a classic I dont have to have it retested - ever.

Also, I am trying to find a exhaust analyzer to rent here in Denver to tune it but can't find one yet.

 

[Dave Russell]

[ QUOTE ]

Looks like I am running very rich. Would the high alt needle help or hurt that? I pulled the vaccum advance and plugged it - no change to idle. Shouldn't that have some impact? Pulled the air pump hose and plugged it - no change to idle - the manual says there shouldn't.

Funny thing too and probably is a diff problem, but when I turn on the lights, I lose about 300 RPMs - goes back after I turn them off. Never had that happen before.

Any suggestions or tricks? Once I get it licensed, as long as its classifed as a classic I dont have to have it retested - ever.

[/ QUOTE ]
Hi AB,
I can't give much specific help. Since air density is about 17% lower at your altitude than at sea level, a leaner needle & all other settings would be in order. I think the vacuum advance comes from a ported source, is not in the picture at idle. The air pump is also out of the picture at idle. If the vacuum advance comes directly from the manifold, it would be in the picture at idle & could be a major source of problems.

losing 300 rpm with the lights on is a bit much. I wouldn't expect more than 100 rpm. This & the apparently unstable idle indicate "something" is wrong with the carb calibration or ignition timing or both. I hope you get it sorted out. I'm sure someone more knowledgeable about the ZS carb will help.
D

 

[Trevor Jessie]

As I stated in the other thread, I know almost nothing about ZS, but is it possible to manually fix the choke in the off position so that you can eliminate that variable? Then, you can adjust the mixture as needed. I pulled this quote from another thread

"Running too lean could cause overheating. You need the
ZS adjusting tool to make coarse changes to the mixture.
Fine changes can be made with the CO idle adjustment
screw on the side of the carb. Once you have the
adjusting tool, remove the damper rod and lock the tool
in place in the damper chamber to avoid tearing the
diaphragm. Turning counter
clockwise leans out the mixture and clockwise enriches it."

and another
"I don't know if you've examined the float height in your float chamber, but it's central to getting the mixture right. (Ignore this next bit if you've
already done it.) This will mean taking the carb out and removing the float chamber. Make sure the chamber is free of all contamination; then ensure that the float is free to rise and fall through its full travel. I once put in a new float, only to find that it interfered with one of the three screws that hold the choke body on, and therefore wasn't rising far enough to shut off fuel flow. Argh. Anyway, check that, and with the carb held upside down, measure the distance from the gasket face on the carb body to the top (bottom, actually) of the float. The distance should be between 0.625 and 0.672. Basically, shoot for 5/8" and you've got it. Adjust this by gently
bending the tab that contacts the pin on the float valve. There should be a picture in your manual, on p.89. Reassemble the float chamber with a new gasket. I tried re-using an old gasket two or three times, back when I tried and then removed a Grose Jet float valve, and ended up with a fuel leak as a result.

Before I forget, you might want to dig into your choke assembly. I may have mentioned before that I recently learned how to overhaul that thing, thanks to Rick Jaskowiak in Hackensack, MN. He fully documented the whole procedure on his website, and this is a definite must-see, as far as I'm concerned. This is vital info, but I've never seen it in any manual. His address
is https://personalpages.tds.net/~jasko/choke/ZSchoke.htm. He's got a full set of color photos and a concise commentary on how things work, and how to put
them right. Simply put, I found out that the tiny little O-ring seal on my choke's enrichment needle was completely deteriorated, and was causing a rich mixture in spite of my best efforts to adjust the carb needle. So be sure to have a look at that. If you have a carb rebuild kit, it should have included that little O-ring. Fortunately, the choke is really easy to
rebuild, with Rick's instructions.

Did you put a new metering needle in your carb? I recently did that, and actually managed to get really near the correct mixture right off the bat. I installed the new needle with the shoulder of the needle holder just barely protruding from the bottom of the air piston. As it turns out, my carb was
about ready for a new needle anyway. There was some wear on the old needle, barely visible, but with the precision tolerances involved I think that little bit of wear was adversely affecting my mixture. Another note here, be sure to tighten up the little set screw that keeps the needle from turning when you adjust it. I once left mine slightly loose, not wanting to
pin the needle in place, and the needle later fell out when I was out driving. That was a show-stopper, and yet another roadside fix. Tighten the set screw up,
because it's got a spring-loaded tip and won't actually lock the needle.

As for mixture adjustment, the old way is to use the lift-the-piston method described below. The more accurate way, and the method documented in both
the Haynes and Factory manuals, is to use an exhaust gas analyzer to get an accurate reading of CO level. Fortunately, a buddy of mine has a Gunson's GasTester that I've used a few times. It's way slick, and I want to buy my own eventually. They're about $200, but they really do take all the guesswork out of setting your mixture. This is a big issue with me, as my car is required to pass an emissions inspection every two years and I want to get it as close as I can. I won't go into the technique for using the GasTester, since it's covered pretty well in Haynes.

As for the "lift-the-piston" method, that's not in the Haynes Spridget manual... but it should get you in the ballpark. The following data comes from another Haynes book that covers just the Zenith carb: Start the
engine, and let it warm up. This assumes that your mixture setting is good enough to let it start... Once it's up to operating temp, use a skinny screwdriver or
something to lift the air piston just a little -- the book says around 0.032". Surely you can eyeball a tolerance like that! (You can't do this with the air filter installed.) The trick here is not to disturb the airflow too much with a thick tool, or with your hand. If the idle speed falls right off, the mix is too lean. Use the Zenith tool to enrich it a
little bit, by turning the wrench part clockwise while firmly holding the outer tube. (make sure the keys at the bottom of the tube are engaged in the slots at the top of the air piston.) Then lift the piston again. Keep trying this until the idle speed rises, then falls, slightly when you lift the piston. Conversely, if you lift the piston and the idle speed increases,
it's too rich. Turn the tool counterclockwise to lean it out a bit, and try again.

As mentioned before, the GasTester is really the best tool to use here. Ideally, you want to measure the mix with the air filter installed, as the filter's slight resistance to airflow will affect the manifold
vacuum, and therefore the behavior of the carb's air piston. You can do that with the GasTester, but not with the "lift-the-piston" trick. Notice that the
Haynes manual has you starting your adjustments with the Fine Idle Screw, which is really the best way to go. If your main needle setting is fairly close, you
can set your mix just with the Fine Idle Screw and not worry about the needle. You should only have to adjust the needle if the needle setting is too far out of range for the Fine Idle Screw to compensate. Really,
the needle adjuster is for coarse adjustment only.

According to the factory manual, the acceptable range of CO content is from 3% to 7% for the 1978 models, with the optimum setting being 5%. I was able to nail that number using the GasTester. This is with the air pump disconnected, by the way, according to the instructions in the manual.

Mixture settings can have some big-time ramifications. If you get it really rich, you can get raw fuel blowing by your rings into the oil pan, and your
oil level will rise as the oil gets thinner and thinner. Not good at all! And if it's too lean, you can cause overheating, detonation, and piston
damage. No fun either.

Well, that was the usual encyclopedia... hope it was helpful!"

 

[abnovak]

Thank for the extensive information. I don't have a gas analyzer (yet) so I did the manual adjust as you discribed. I found it in my Weber book as well.

I leaned the mixture quite a bit. At first, it seemed to run pretty well, had a smooth exhaust no hestitation or "burps". I let it run about 20 min before I left, drove about 10 miles then RPM started to drop below 500 at the lights and it threatened to stall. Now it hestitates when u get any RPMs so I think its way too lean.

I turned the needle counter-clockwise about 2/3 of a turn. The books says not to do more then 1 full turn or you run the risk of the needle coming out. Should I do more? I am also still checking to make sure I have the right needle.

And, here the punch line. I failed again - improved but failed. CO went from 7.1 to 5.8 at idle and at 2500 RPM is stayed virtually the same at 5.8 I need a 2 or better. HC PPM actualy got much better from 932 to 514 at idle - I need 400.

Any other suggestions?

In about a month, I am going to get an analyzer. Good investment considering I have two other vehicles I have to do this on as well.

 

[Fokkerfreighter]

People will probably not like this, but I have done this successfully in the past to get a car through emmissions here in Oregon. Run the car very very low on gas, get a gallon of isoporopyl alcohol, pour it in the gas tank. The car will have never run cleaner. It worked twice for me with a car that was on its last leg and should not have ever passed emmissions. I understand it is hard on all of the seals, and hoses, but it is a really quick half a**ed fix.

 

[crj7driver]

Where did you get the information stating that once you get it to pass you will not have to get it retested? As far as I know in Denver only pre 1959 cars are exempt. I am interested in this because I need to get my '70 TR6 to pass in Denver as well, and if it is only a one time deal great.

 

[abnovak]

Dept of Motor Vehicles told me that once I get it licensed as a Classic Vehicle (which lasts for 5 yrs) as long as I reissue it as a Classic I dont have to have it tested again. The license fees are much more upfront but are cheaper over the long run. And, I checked no limit on mileage either (insurance restrictions aside). This was from Adams County office off 120th

Do you have a mechanic in Denver that might help me get this past emissions?

 

[crj7driver]

yeah, Sportscar Craftsmen, just south of I-70 between Wadsworth and Kipling. 8065 W 48th Ave. Wheat Ridge, co

303 422 9272

really nice knowledgable guys, immaculate shop

they have an exhaust spectrum analyzer at the shop and can even take it and get it tested for you.

 

[Trevor Jessie]

Hmm... two "newbies" solving each others problems. Fair enough, but you have to report back on what the solution was.

 

[donandmax]

Speaking of ZS carbs.(?) Does anyone know if that "knob" on the right side of the carb.(standing by fender and looking down)is ajustable or should it be screwed all the way down tight. It has a small screw in the middle of it used for adjusting co. Mine is loose it is octagon shaped if I screw it down it does affect the engine idle. But I'm not sure if that white octagon shaped knob itself is part of the adjustment or if only the little screw is. By the way yurning that little screw seems to have no effect on the engine at all. Unless it takes a spectrum analizer to tell.
Thanls
Don

 

[jcatnite]

Haynes doesn't do a good job of labeling that side of the carb. I'm assuming that the screw you are talking about is the "air regulator". I've not noticed any adjustments making any difference either. There is a screw just below it and back towards the engine a bit. I think that is something called the "decel valve"? Not sure exactly what it does either. Perhaps there is someone who can enlighten us...lol
JC