Hi!

Had my exhaust sniffed yesterday for my first inspection. Idle CO at 750-800rpm in park is at 4.8vol%, both exhaust pipes. Value needs to be at a maximum of 4.5% for 1970 vehicles.

A '72 El Camino was in their database, Chevy small block with a QJet, had 4.0/4.2% at measurement and the guys said QJets should normally be able to get under 4.5% quite easily.

While I set my ignition timings already, I have no ringing and the engine isn't too far on the rich side, I actually wanted to rebuild my carb (rebuild set already here) after registration without hassle and not rip it apart now before May 6th.

Question:

Does anybody have experience in setting idle lean/rich in combination with live CO measurement? Do I have a chance to get down to or below 4.5% with just playing with the idle mixture screws?

I could get away with a rough running idle for the printout and go back to my current settings after that.

 

Leaning out your idle mixture screws should bring down your CO at idle. 4.8% is high(rich) on a stock engine. It would probably only take about 1/2 turn in on each screw to get you below the 4.5% mark. You want to turn them in until you get just a roughness in the idle then back out just enough until it smooths out as a rule of thumb. Do they also test for HC?

 

another tip...put the car on defrost so the idle will pick up a couple hundreds

 

My car goes through emissions testing every year. The CO idle limit is 5.0% and I easily pass that, typically with a value below 0.5%. Your engine must need some tuning if you are getting 4.8% at idle.

What distributor are you using and what is your initial setting?

Things that really help my engine are:
- disconnect the vacuum advance
- set the initial advance to 10º
- use low octane fuel

I have a spreadsheet with the test results for the past 15 years and I see an increase in CO with high octane (91) fuel vs. low octane (87) fuel. Another tip is to add methanol or ethanol (I use E-85) so there is about 20-25% alcohol. This one thing REALLY drops the readings for both CO and HC. I've had as low as 37 ppm HC and 0.12% CO with this tuning.

 

You have an over rich condition either caused by a float-needle and seat problem or the mixture screws are are out too far.Nick

 

Yes, by far - but I don't have any experience for 70's V8s so far.

So it's possible. I'll adjust it on Monday/Tuesday with the sniffer connected when I'm there again.
Just idle CO without catalytic converter.

Now that's a number.

New Pertronix, new spark plugs and wires, stock QJet, Stock air cleaner and housing.

~10 to 12 degrees @ 1000 to 1200rpm with vacuum connected.

Yikes. I'm on 102 Octane plus lead replacement for now.

So I'll do my homework and let them sniff again Monday or Tuesday.

Thanks, Gentlemen!

Stefan

 

Your octane is different from our octane. This misunderstanding has destroyed engines.

You use the Research (RON) system, while we use the Anti-Knock Index (AKI or RON+MON/2) system.
The RON rating is usually about 4-5 points higher than the AKI system for the same fuel.
Your system is the system we used to use when these cars were made.

The average gas station in the US now sells gasoline between 87 and 93 octane, which corresponds roughly to 92 to 98 octane on your side of the pond.
Since our premium-fuel cars were made to run on 100 octane (102 or 103 octane for the W-30s and other high-performance cars), none of the gas commonly available over here has enough octane fo them, but it is close.

If you have a premium fuel 350 (one that came from the factory with a four barrel carb.), then, in theory at least, you should only need 100 octane.

You do not need a lead substitute unless you are constantly drag racing or towing a heavy trailer through the Alps, but are certainly welcome to use one if you prefer.

- Eric

 

Sorry, Eric - I know it but forgot to mention it: "At least 102ROZ, no bio Ethanol but bio Ether", so 97/98 Octane on your side of the globe.

Lunch break update:

Warmed her up, turned both idle mixture screws in 2 and a half turns exactly. While I didn't check what position(s) I started at (bummer!), both screws give a rough idle after another quarter turn.

Now, shame on me - of course it's too rich after dumping the shiny open edelbrock air filter housing in favour of a stock housing.

I'll let them sniff my rear end again after work today.

 

Passed: 1.791vol% at 610rpm. With very old oil, 102ROZ and no further tricks but the idle mixture screws.

 

Congrats on passing the test. Is it ready for registration now?

 

Congrats your on the road

 

This is great info. I always joked about running inspections on moonshine.

 

I figure if the state is going to emissions test a 40+ year old car that drives a few thousand miles per year then I will play their game, but not by their rules.

These emissions tests were implemented by the same geniuses who decided to start monitoring the air quality for particulate matter. Well guess what, it's a desert and the wind blows, so there are gonna be particulates in the air. Dumbasses. Their solution to the "problem" was to mandate paving all roads within the county. Pretty soon we'll have to pave over the entire desert to be in "compliance".

 

Uhhh, while I passed the emissions test and the technical part, paperwork is not yet done.

The Inspection engineer cowardly refuses to fill in the 1970 maximum for loudness and required a measurement for that - next Tuesday.

Other than that: OK.

Stefan