My buddy needs help to pass the test at idle. Any suggestions. It may be running a little fast. Timing is 20* at idle. 40*at 3000. This is at Phoenix Arizona. Any and all suggestions appreciated. Thanks. Kim
Emissions Test
- Thread starter oldkimmer
- Start date
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That is no where near enough information. It’s a ‘73 Plymouth, and it’s putting too many unburned hydrocarbons into the exhaust pipe at idle, that’s all you’re giving us. What engine is in it? Stock, modified, what modifications? Could be darn near anything, running rich at idle, carrying a dead cylinder, timing is off, plug is fouled… I mean nearly anything. 20* advanced at idle is too much per the factory, but that only applies if it’s bone stock.
What emission standard is even being applied to a ‘73 Plymouth to begin with? You may have to familiarize us with the relevant standards there, even in California there’s no emission testing for anything pre-‘75.
What emission standard is even being applied to a ‘73 Plymouth to begin with? You may have to familiarize us with the relevant standards there, even in California there’s no emission testing for anything pre-‘75.
The smog guy that I have been using for 20 years has me put Chevron or Shell gas in the tank and drive the car for at least a half hour. He makes sure that the car doesn’t sit very long before he tests it. This was for my old 1982 Mazda B2200. My pre-1975 cars are smog exempt.
mopowers
Well-Known Member
Lean out the idle circuit - a lot.
thesiren74
Well-Known Member
I'm so glad we don't test anything older than 1996 in Wisconsin anymore man that sucked!
What a lot of guys did here was lean out the carb and back timing and get it nice and warm,.
What a lot of guys did here was lean out the carb and back timing and get it nice and warm,.
They are doing smog tests on a 48 year old car??? I live in King County, WA where Seattle is and even here they don't smog test cars over 30 years old.....
thesiren74
Well-Known Member
I passed all the time with a wornout 318 the trick was to have small holes in the exhaust so it would pull fresh air with the exhaust it passed better than newer cars lol
He is trying to get license plates for it. It’s a Canadian car. 73 Cuda 340. 1970 340. It has about 100 miles on it since I built it. 10.5 measured compression. Speed Pro pistons. Speedmaster cnc heads. LD340 intake. 650 Brawler double pumper carb. Howards cam. Complete TTI headers and complete exhaust. 4 speed car.
Phreakish
Well-Known Member
Slow the idle and lean the idle mix. It's only the HC failing at idle, and not horribly. 900 instead of 400.. Dead cylinders or other issues would be much higher I think.
Having the engine super hot is definitely a good idea. I'd be running a 205 thermostat to ensure a pass.
Having the engine super hot is definitely a good idea. I'd be running a 205 thermostat to ensure a pass.
borrow a simple 500cfm edelbrock for a day?
Red's '72 Dart
Well-Known Member
Run the idle air fuel mixture screw all the way in, than 1 1/4 turns out. Set idle and timming at 5 before dtc. Tirm air/mixture screw in so the engine just starts to shutter. Dirve car and adjust timing untill you get light pinging. Put a bottle of octane booster in it. Drive it hard to the testing site.
Now that makes more sense!
It boggles my mind a bit why an engine that heavily modified is being tested to a factory 1973 emission standard, but whatever.
The idle will have to be leaned out a ton, and it will need to run HOT. The double pumper likely isn’t helping, even at idle.
It’s not gonna like it. Lean on the mixture, retarded on the timing and about ready to overheat.
Not horribly? It’s more than doubling the hydrocarbon output of a factory 1973 engine. ‘73 was still pre-cat and all that other garbage, that’s a pretty high HC count to begin with.
Now having the engine specs it makes sense, that thing is probably close to double the horsepower from a factory 340 in ‘73, so moving twice as much air and fuel too. Shouldn’t be that rich, but idle isn’t where that engine is happy.
I will say that I didn’t get a chance to do any tuning on it. He thought it ran great and wanted to put some miles on it.
Thanks for the replies guys. Kim
Phreakish
Well-Known Member
I say not horrible because I've seen a stuck injector cause a reading over 10k. A friend had a car with a kjetronic that was slightly out, and read 3600. We adjusted idle mix from 12.3 to 13.7 and it cleaned up to under 400.
For a cammed small block, 900 isn't that bad IMO. It'll need leaned way out, but it'll probably run there. I'd try it with a nominal idle timing. Too much advance will push up the nox, not enough will increase CO.
I don't see a nox reading, so I might be inclined to keep it at 20 and just lean to max rpm, then lower the idle as much as it can be while happy. I'd also make sure the pcv is good and maybe even cheat by letting it suck clean air...
Ironracer
Gearhead
Makes sense
It is the ign timing, too much. It is doing two things: increases the oxides of nitrogen & increases hydrocarbons.
For the test, he should reduce init timing to about 0-4* BTDC & disconnect MVA if he is using it.
For the test, he should reduce init timing to about 0-4* BTDC & disconnect MVA if he is using it.
Phreakish
Well-Known Member
Does advance increase HC? I would think more time for the mix to burn would reduce HC.. Especially with a lean mix.
My understanding with retarded igniton in the 70s was to reduce NOX which caused acid rain, and is formed at the higher temperatures reached with high compression or modestly lean mixes (which burn hotter).
Phreakish
Well-Known Member
I honestly didn't think regarding the ignition would help, but apparently it's experimentally proven!
Does make some sense I suppose. I had assumed retarding the ignition only help when a catalyst is involved, but a very well heated pipe/exhaust can work very well as an afterburner too, even without a catalyst.
Phreakish
Well-Known Member
I screwed up setting the timing on a new hotrod this fall. Wound up at 5 deg BTDC. It's got side pipes. Retarded ignition definitely keeps heat in the exhaust! It also made the egine run-on after I shut it off... I later set it up closer to 18, and I can damn near hold the pipes after I shut it down.
Makes sense. Get the exhaust hot enough, and anything coming out of the port will definitely burn off.
I honestly had thought that a lean mix with lots of time to burn wouldn't leave much left in the exhaust other than a higher CO and NOX content. Learn something new everyday!
rustycowll69
Well-Known Member
Yes, just lean it out. If it has a PCV valve, leave the hose attached and just pull the valve out of the grommet in the valve cover and lay it loose on the top of the valve cover(for the test only).
Put a converter (s) with bolt in flange on it.
After the test, go home and take it off, use a prefabbed Section of pipe in place of the converter.
IIRC Rumblefish posted sucess with this idea
After the test, go home and take it off, use a prefabbed Section of pipe in place of the converter.
IIRC Rumblefish posted sucess with this idea
Just search around for a shop that will do the right thing. The first shop didn't do him any favors by failing him, now his VIN is in the system and Big Brother is watching.
I used to conduct NY state emissions inspections in the 80s and 90s, when tolerances were unreasonable and the state had a video camera watching over the bay.
I was able to wiggle results then, I'm sure it can be done today.
Ya know, a few limited use classic cars aren't gonna amount to much CO or HCs in this world.
I used to conduct NY state emissions inspections in the 80s and 90s, when tolerances were unreasonable and the state had a video camera watching over the bay.
I was able to wiggle results then, I'm sure it can be done today.
Ya know, a few limited use classic cars aren't gonna amount to much CO or HCs in this world.
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