My car is an 89 RS with a built 355, comp cams, vortec heads, long tube headers...tons of mods, basically a hot rod. In Georgia, I have to pass emissions to register it (live in Marietta).
It has a Demon carb on it that I belive is running rich. I spent $600 getting catalytic converters and basically a full magnaflow exhaust put on it and attempted an emissions test. It has to pass a 15mph test and a 25 mph sniffer test on the dyno.
My HC passed: 107read/142 allowed 25mph.....128 read/148 allowed 15mph
My CO failed: 7.81 read/0.92 allowed 25 mph....7.92/0.82 allowed 15 mph
My NOx passed: 24 read/1092 allowed 25 mph....29 read/1124 allowed 15 mph
CO+CO2 was about 17.2%....test minimum is 6.0

I assume it running extremely rich and dont want to burn out the new race cats...car has no O2 sensor or computer for that matter.

Any ideas on how to pass emissions? The mechanical cost waiver probably won't work in my favor since it has to be inspected, and as i said...its not stock!

Thanks for your help,
Newbee Bryan

 

Get a wide band o2 system and check how rich you are running.

 

Sad to say it, but your car will never pass a sniffer test running a carb. Your car's year only came with EFI, so those are the number that they will use. So you'd need your O2 sensor, computer hooked up, EFI installed, cats installed etc. To run a carb on these cars and pass emissions, you'd need to run a CCQjet, tuned and an early 80's computer to run it. But...your car isn't one that ever came with a carb...so that's sort of out of the question. Is there a "hotrod" friendly inspector near you? I'd check with some of the local car clubs and see. Maybe they could help you find a hotrod friendly inspector who could "assist' in passing the emissions test?

 

What do the plugs look like? Does it smell rich at idle? What heat range plugs? What is your timing at idle and low RPMS? What comp cam? You can lean that carb out and mess with the ignition (and maybe even the heat range of the plugs). Can you get friendly with an inspector (or garage with test equipment) so you can make some trial runs to see if your changes are helping? Just some thoughts. No reason you can't get there with a carb. FI doesn't magically make combustion cleaner. It just meters the fuel diferently than a carburetor. If the carb and FI are supplying the correct amount of fuel, the emissions should be the same.

 

i will have to dig the build sheet out to get the exact cam specs, but i was told a few times that it will always be too rich with the demon carb on it...and was told to get a holley 650. im pretty sure the demon is a 750 which in all reality it too much carb for a 355. i can get a 650 pretty cheap, so i may go that route and fiddle with the timing.
at approx 900 rpm idle (its a little lumpy with the cam)..timing is between 12-15 deg btdc. ill pull the plugs(and replace them) monday. it does smell rich at idle and stumbles a little off idle and during light throttle cruise in 5th gear. (its a 5 speed).
it had 1 hour new catco racing cats on it when the emissions test was done...and i really want to get it leaned out so that i dont blow the cats out in a week, and also to get the carb dialed in correctly for driveability as i do plan on driving it often.

 

12-15* advance isn't enough...especially with a lumpy cam (specs would be great). Do you have vacuum advance hooked up with your distributor? Lets get the timing sorted out first before we touch anything on the carb. I can help you dial in the Demon. Do you know which model you have? Leaning out idle is fairly easy. However, if you don't have enough timing advance, you will never get a lean idle.

 

Even if he figures out the lean/rich I don't think he'll get it to pass the emissions though it may run well.

 

We'll see. I think he can get there...if the cam isn't too radical and the heads/intake aren't mismatched. Of course, if the compression is real high, he may fail on NOx.

 

sorry its been a few days...
heres the update.

cam is a comp cams flat-tappet hydraulic: 230/230@.050 lift, lift: .480/.480 lobe separation 110
com cams high rev lifters
speedpro hyper-eutectic 4v releif flat top 10:1 pistons
comp cams lt-1 springs and keepers
edelbrock performer rpm intake manifold
msd ignition (6al)

what ive done so far: replaced the demon carb with a holley 600 cfm tuned and timed by ear. took it for another emission test and retarded the timing to 0 deg (it was idling at 450 rpm)and my results were:

HC ppm 34 read, 144 allowed (25mph test) 28 read, 148 allowed (15 mph test)
CO% 2.09 read, 0.92 allowed (25 mph) 1.14 read, 0.83 allowed (15 mph)
NOx 7 read, 1014 allowed (25 mph) 6 read, 1110 allowed (15 mph)
co+co2 15.9 read, 6 min (25 mph test), 15.5 read, 6 min (15 mph)

still the only thing that failed is the co%, but it was much better, what else can i do to get the last little bit of co out to pass? will those magic potions like guaranteed to pass work at all? i plan on trying again friday morning after an oil change. i got excited that i was pretty close, but and getting pissed and may cut my losses and sell the damn car if i cant get it there, im reaching poor and cant afford to dump much more money into it.

also, any idea on where my idle timing should be: i was told around 10 deg btdc as a starting point and fine tuning from there...and it should idle at 1000 rpm???

thanks,
bryan

 

also, should i unplug the vacuum advance during the test and leave the port open or should i leave it as is? i plan on taking off the air cleaner for a little more air intake, will that help?

 

Too much fuel and not enough air...that causes high CO. You need to get your base timing up. At idle (around 800 RPM or so), you should be reading closer to 40 degrees BTDC with the vacuum advance hooked up (your base timing without the vacuum will be closer to 18*). This will allow you to close up the throttle blades and prevent the carb at low speed from drawing in fuel from the transition circuit. Make sure your full throttle timing doesn't go over about 36* (under full throttle, the vacuum advance is not active).

After you do this, the little idle mixture screws on the front of the carb should work for setting the AF at idle. Right now, turning those screws probably does nothing for you.

 

my cam is similar and i only needed 12* initial, ported vacuum, 66 jets on a Speed Demon 650, just close does idle screws as much as you can, it worked for me

 

pancherj... are you talking about running correctly and if so on a ported vacuum? if so thank you that will be very helpful when i try to get it right for driving out of the bay after the test (couldnt get it right by ear and it ran like crap all the way home). camarito... i am currently just trying to get it to pass emissions. i did a ton better by just retarding the timing to 0deg. i am trying to lean it out just a bit more, should i pull the vacuum hose off the advance and leave it to pull more air during the test (effectivly making an intentional vacuum leak)? or pull it and plug the vacuum port? or leave it correctly installed? will changing the oil make a noteable difference or changing the plugs?
i am going to change the oil, run crc guaranteed to pass through it, turn the idle mixture screws in a little, pour some seafoam in the fuel tank, drop the timing to 0 deg and turn up the idle screw to keep her running...you think that will drop it 1.2%?

 

leave your vacuum advance hooked up to ported vacuum and check what the timing is at 2500-3000 RPM. Run as much spark advance as you can without pinging. Then you need drop the jet size down in the front( if you have a carb with no secondary metering block you cannot change the jets) I'd say drop it 4-6 jet sizes and make sure the float level isn't too high. You got the HC's down now you need to lean her our some more to drop the CO.

side note...when the cam was installed was it installed straight up or advanced? I've found those comp cams like to be installed 2-4 degrees advanced from where they tell you to and makes the power band come in sooner( if the cam card says install on 106 installed C/L advance it to 100-102 intake C/L) just my .02

 

with 0 advance you can't lean the idle enough without stalling, it's not just the idle screws you have to close it's also the primary and secondary butterflies, its important to stay on the idle circuit, opening the butterflies will expose the transition slots too much and you start pulling fuel.
leave the vacuum advance connected, changing the oil helps if you have a pcv valve, new plugs help too if you were running rich before.

 

so youre saying i should advance the timing? isnt that counter-intuitive for reducing co emissions, or do i have it backwards?....i have tons of wiggle room on the other parameters of the test, i mean im really barely even producing hc or nox...currently only concerned with co

 

you think the isoprpyl alcohol crap that all the california guys use will get it down?
.i currently run 93 octane, last test i put some b12 chemtool (cheap seafoam) in the tank, i really just want a band-aid pass since i will never have to pass again

 

advancing timing helps reduce CO but there is a point where too much advance will cause a misfire and increase HC's. Idealy your mechanical advance should be around 36* total @ 3,000RPM and add the 10-20* vacuum advance should be around 46-56*total. More important drop the jet size in the primary that will drop CO. Remember CO is a by product of combustion you want to make it as efficient as possible. It can be done I used to perform smog inspections and repair failed vehicles in Ca.

 

92rs4us... i dont have the parts on hand to change out the jets...or the ability to check the timing past 16* btdc (last timing mark is 16), so if i put the mixture screws at factory setting (1.5 turns out from seat), what should my timing be with the vac advance pulled off and plugged? and then how far should i advance it for the test to kill the co emissions? i am planning an oil and plug change in the morning, drive a few minutes, get it to 1/2 tank, throw a bottle of isopropyl alcohol in it, give it hell for a few...set my timing where it needs to be to pass (hopefully you can give me this setting) and run the test. ??????

 

my timing plan is to set the timing at my best guess at 18* with the vacuum advance unplugged , turn the idle screw to get it at about 950rpm and then lean the idle mixture screws as much as possible whilst still keeping it running. thats what im gathering from all the responses.
And since i havent said it yet, Thank You everyone for the help/advice thus far...already the best forum ive been on.

 

UPDATE
passed my emissions with flying colors...
i set the timing at 16*btdc, changed the plugs(they were jet black with carbon) and oil, took the air cleaner off, set the mixture screws at 1.5 turns out (factory setting) and here are the numbers:
hc: 25 read, 144 allowed 25mph...9 read, 148 allowed 15 mph
co: 0.01 read, 0.92 allowed 25mph, 0.01 read, 0.83 allowed 15mph
NOx: 181 read, 1014 allowed 25mph, 141 read, 1110 allowed 15mph
co+co%: 14.6, 6.0 min 25 mph, 15.1, 6.0 min 15 mph

so now my question/concern is that it is running really lean..more than i would like it to...should i put the Demon 750 back on and tune it, or stick with the holley 600?

i will street drive it mostly, so i want the best mpg / with performance also
and should I run 93 octane? thats what ive been running, but dont see it as necessary unless thats what it needs.

you guys are awesome...props to 92rs4us for getting me do advance the timing even though i didnt think it would work.

 

wow does are some good numbers, i know it's frustrating I've been there specially when some of my friends told me "you never pass emissions legally with that monster". I' happy for you
I would keep the 600 for a while, tune it for street use and latter on swap it for the 750 then you can tell the difference
I use regular gas and i never had a problem with it but my initial timing is 12*

 

thanks camarito... i think ill ween my car off premium...a few tanks of mid-grade...then finally to regular old 87. I didnt think it needed premium because its not boosted...i know its a performance engine, but still.
and btw i also put my initial timing at 12* and cranked the mixture screws out to 2.25 turns...i think it was too lean at 16* and kinda surged in all gears with light throttle, but will still pull hard with a heavy foot. i guess ill have to keep fiddling with it until i get it right for driving.

 

Good for you! I was pretty confident you could get there. As I said, there is no magic to fuel injection that makes the combustion process better than a carb...assuming the carb is giving the engine the right amount of fuel.

Which model Demon 750 do you have? If it is the one with the annular boosters, I would definitely switch back to that. The light stumble could have been a lean issue, or too much vacuum advance while lugging the engine (easy to do with a stick shift). It also may need slightly richer primary jets.

 

Good job on getting her to pass! if you can find somebody with a timing light with an advance dial or a snap on digital timing light you can check your total advance. Setting the initial timing is one thing, but for best performance you need to see what the timing is at 3,000RPM. All the advance needs to be in by then, if it continues to advance it can cause detonation. Every engine is different so whatever the engine likes that gives it the best performance will work. With a performance cam like yours it requires more initial timing to run properly, with so much overlap it reeks havoc in the incoming air/fuel mix and is not efficient. I usually set the timing up so you can get the most initial timing without causing the engine to "grunt" when starting. And at 3,000RPM I like to set it at 34-36* total(without vacuum advance hooked up.) for a street car. With the vacuum advance they usually add about 20* additional under light throttle cruising for max fuel efficiency. Again try to run as much as you can without pinging.

 

ok well i put the demon back on...took me forever to get her started and still havent got it dialed in to run decently...i had to turn the idle screw a bunch to get the idle up to 900 at 16*btdc, all 4 mixture screws 2 turns out.
it was starting to rain and was dark out so after a short test run...bucking and sputtering except under heavy throttle....i decided to park it, and got out to smell the exhaust
HUGE PROBLEM!!!! the cats touched some pinestraw and caught it and the cats on fire!!!!
i was able to move the car and extinguish both, but that was nearly very bad!
now i am very concerned that there is something wrong to cause the fire, or does that actually happen when cats sit on damp pinestraw??? this is the first time its happened and i park there all the time!

 

also, my idle timing doesnt change one bit with the vacuum advance hooked up or not

 

WOW that's bad!!! that demon is dumping way too much fuel get rid of that thing!!! The cats were glowing red hot from the excess amount of fuel being burned up in the cats for it to catch the pinestraw on fire. The vacuum advance doesn't work at idle when it's hooked up to a ported vacuum source. Ported vacuum means no vacuum until you open the throttle blades off idle. It's designed to give the extra amount of spark timing off idle low speed cruising RPM. Once you mash the gas the vacuum goes away but the mechanical advance in the distributor takes over.

 

well i might have fixed it / figured out the problem, started her up to see it the cats would glow after a few minutes and the exhaust smelled like pure gasoline...turned the mixture screws in and idle increased! now they are at 3/4 turn out and i was able to turn the idle speed screw almost all the way in...and it ran like a scalded dog up the street for the first time in a while. im going to adjust the float level tomorrow (its really low) and try to lean out the idle a little more. when i get paid next week im going to but a vacuum guage and try to learn to tune it with that...since im told that it the proper way to set the mixture and timing. any ideas on how to do that?

 

and what should my fuel pressure be, it a little jumpy but generally betwen 9-10 psi? ive read that 6 psi is normal, so im assuming i can turn it down with this fancy fuel pressure regulator that i have

 

7psi is ideal. You can get by with more psi if you have high flow needles and seats but you don't need it. You can go as low as 6psi at idle.

As for vacuum tuning, hook up the gage to manifold vacuum(vacuum with the throttle plates closed at idle) then you adjust the idle mix screws to obtain the best idle vacuum reading, then turn them back in 1/2 turn for best lean idle. They both should be about the same but don't be surprised if they are not. Remember when turning them in it leans out and RPM drops, turning them out richens them, RPM goes up but then will start dropping due to being too rich.

 

Which model Demon?? I have a 750 Mighty Demon (annular boosters) on my 350 and I love it. However, it took a lot of tuning to get it just right (changes to the IFR's, HSAB's, idle jets and enlarging the PVCR's so I could minimize my main jets). My model also has the idle air bypass system, but I don't use it.

The best change I made: Modifying my HEI to limit mechanical advance to 18* and running 18* initial (36* total). With vacuum advance, I idle and light cruise at 52* advance. My idle vacuum went up to 12 inches. My cam is a little bit bigger than yours.

 

i have my initial timing at 16*, and the carb is a speed demon 750ve, no annular boosters. i also have that idle air bypass screw, but have no idea how to set it, so i havent touched it...i guess ill try to lower my fuel pressure a little, and then readjust my idle mixture properly with the vacuum gauge.

 

You probably wont need the idle air bypass system. Get the fuel pressure down to around 7psi. Make sure the floats are set around the middle of the sight window. If it were me, I would take the carb off, flip it over and then set the primary and secondary throttle blades so that a small window (almost a square) of the transition slots is showing. This will be your baseline. If you need to adjust the idle speed screws more than 1/2 turn open from this spot, then you should turn to the idle air bypass to get the desired idle RPM instead. Lastly, use the vacuum gauge to set the idle mixture screws.

 

Lowered the fuel pressure... I will do the mixture screws tomorrow as well as reset the idle screw(it should be make a tiny box when reset right?). Will changing the sprayer do anything, I have a bunch of the differently numbered currently a #31 installed?

 

The shooters help the transition when going to more throttle. Unless you have a stumble, the #31's should be good for now.

Set both idle screws (primary and secondaries) to get the small square. If you need to open much more from that point to get your desired idle, use the idle air bypass instead. Getting the idle and transition circuits of the carb correct is the hardest part. WOT is the easiest. An O2 sensor will help, but they aren't very useful for idle if you have a larger camshaft.

 

well today was the first time i got into the throttle since the carb change...under heavy throttle it feels like its holding back...maybe stumbling, cant tell if its too much or little fuel. it pulls great under light throttle. I know the secondary idle screw is set so its a little box, the primary one was also when i put it back on, but i had to adjust the screw to get it to idle initially, and i forgot how many turns out i went. guess i get to redo that. i think i may need to retard my initial timing a little but i think ill wait until i get the vacuum gauge. im getting frustrated at this point because im just now learning carbs and am getting tired of redoing everything....although i really do appreciate the help, otherwise i would be lost!

 

also, i have a pcv valve, but the tube just goes nowhere, should i connect that? if so, to what?

 

I like to run a PCV system on my car. I have it hooked into a fitting on the intake manifold.

Carbs take some work to get running correctly...so does FI. Once you get it all sorted out, you will be good to go. Plus, when something is acting up, you'll have a better understanding of what it is.

If the car is hesitating under hard acceleration, I would say the jets need to go up a few sizes. The shooters will only cause a stumble right when the throttle is punched.

What are the ratings on your power valves?? (I assume you have two...primary and secondaries).

 

well i retarded the timing to 12* and it pulls a little better but has a low idle, and it kinda bucks when i shut it off sometimes. maybe i should go for more than 16* advance? should i hook the pcv to the constant vacuum on the carb? i dont see anywhere on the manifold where it should be connected. the only thing i see on the manifold is and empty hole in front of the distributor (i guess something should be screwed into it?). do i possibly have a vacuum leak? if possible can you send me a pic of your pcv setup, i know it not being hooked up is a problem, because the breather on the other side smokes and drips a little oil on the valve cover.

 

also, i assume the pcv is hollowed out, no rattle like any other car. and i have no idea what the rating on the power valves are, or what the power valves are for that matter

 

My car is about 50 miles from home right now. I have a fitting that screws into my Performer RPM Airgap and I run the PCV and my power brakes off of that. The PCV has the valve in it (not hollowed out). I use a PCV valve from a 1970 Z28 camaro (lower vacuum rating).

I think 16* should be just about perfect for you. You could have a vacuum leak, always double check that.

The power valve is what provides extra fuel to the motor when under hard acceleration. Many people assume the jets serve this purpose, but that isn't totally true. Under power, your vacuum drops and the PV opens allowing extra fuel through the power valve restriction (it is a small hole inside the PV orifice).

 

well i got the pcv figured out, and got it running pretty good...i think the holding back feeling might be my cat converters...they glow bright red, so im assuming after two weeks...they are done! now to find someone to remove them or hollow them out since i shouldnt have to pass emissions again...ever!

 

Glowing red...may mean they are seeing too much raw fuel. The only time I ever turned a pair red was on a newer grand am that was dumping way too much fuel. I don't think too lean would get them hot (nothing to light off)...although I could be wrong. I could see retarded timing causing them to get hot too.

What do your plugs look like?

 

One week old plugs are carbon black and smell like gas.... I cant win, with the butterflies closed to a box, mixture screws at 3/4 turn out, timing at 16 btdc .... it idles at 450 rpm, and I have to turn the idle screws to keep her on, thus I assume making it rich, vacuum oz between 11-13 psi. Argh this is annoying,I gguess my new cats are already clogged?

 

If the plugs are bad a misfiring, that would allow raw fuel down into the cats. Did they turn red just idling or after you were driving around?

 

Just idling up to temp, smelled funny so I looked under and they were glowing red

 

Well, it seems then that you are still rich at idle. I would up the base timing some more (and what is it reading at idle with vacuum advance hooked up?). With this, you can probably close the throttle blades a little more and use the idle bypass circuit to help lean it out some.

What fuel pressure are you running? Where are the floats set? Oh, and get some fresh plugs in there so you aren't trying to tune out a misfire.

 

Initial timing at 18, still seems rich, i can't seem to get a hold of an advance timing light. I am getting the cats checked right now, but it plumes dark smoke out at idle until its warmed up. I guess that could be the pcv. But I don't want to destroy anything internal. Should I just put the 600 back on and try to tune that... I'm assuming I can run less initial timing with it? I'm beyond my frustration level and have it up for sale locally.

 

The size of the carb should have no impact on the timing. Are you saying it is showing 18* BTDC with the vacuum advance hooked up? If that is true, the timing is way off.

If you are all of the sudden dumping in fuel at idle, I would suspect a stuck float 1st and a leaking PV gasket 2nd. It wasn't behaving like this when you passed the emissions test (or was it?), so something has changed.