I need help! I have a 73 240, new to me. I took it in to get it inspected (new jersey) with the old flattop carbs, and it failed emissions. HC high and CO high. No problem, I had planned to swap the carbs for early round-tops, which I did (new 3-screws from ztherapy). Not sure I got the mixture right, but it seemed to run okay, idle at about 800-850.

Failed again, CO within spec (.57%, but HC thru the roof, almost six times the earlier readout, ten plus times allowable spec.

If the only change was the carbs, what happened?

I adjusted the mixture screw richer and richer, and never got a condition where lifting the piston caused no change in rpms; it always made the rpms drop. And I was way past 4 turns out from max lean.

All the emissions stuff is off and plugged, no air pump, egr, etc.

I'd like to be able to tune this car without the mechanic, but right now it seems I need someone with an exhaust analyzer.

Ay thoughts would be appreciated.

peter

73 240

You didn't say if you had completed a complete "tune-up" prior to your first emissions testing. It is important to have everything else in proper working order BEFORE attempting to adjust the carbs. This means checking plugs, points, wires and valve clearances. Did you balance the carbs before setting the mixture?

Here is what emission test result indicate:

CO tells about the ratio of fuel to air, basically richness or leanness. It doesn't necessarily tell us about how efficiently the mixture is being burned.

HC tells how much of the available fuel was NOT burned. (High HC = sooty smoke) Low HC is good (no soot). High HC is the result of incomplete burning of the fuel mixture. High HC can result from anything causing incomplete combustion.

O2 tells how much oxygen is left over, normally 1 to 2 percent. O2 emissions should be fairly stable until the air/fuel ratio goes above 14.7:1, then they rise quickly. That makes O2 a good indicator of a lean condition.

CO2 is a measure of combustion efficiency. High CO2 is a good indication of combustion efficiency, and CO2 readings will peak when the air fuel ratio is at its highest efficiency.

I have new spark plugs, pertronix ignitor and coil. I need to check the valve clearances. I did balance the carbs with a uni-syn.

Mostly I am trying to figure out why the big difference between the two inspections, with maybe a month between them, and a carb swap.

My assumption.... oops, don't go there. I guess I should double check my timing as well, as the prior mechanic may have just set it to run okay with the old carbs.

Thanks for the info on exhaust gases, that's helpful.

Peter

I always seem to have trouble with my 73 passing emissions. I try to set my carbs according to the procedure and then the HC are too high. My carbs probably need to to be overhauled, but I can't afford the Ztherapy treatment (translated: my wife says it too expensive).

I recently purchased a ColorTune off the Internet for $40. Cute little toy that allows you to see into the combustion chamber. You then set the fuel/air mixture by the color of the flame. I am pretty tickled with it, and my Z passed emissions with plenty of room to spare.

the Colortune sounds neat. Did it work? It sounds like a good way to set the air-fuel ratio, which is a big problem for many of us, especially those with e.f.i.

thx

On my EFI cars, a clean cat, fresh oil, a clean air filter, a dose of Lucas fuel treatment, and they always pass.

Your car has a cadillactic converter?

I was referring to those who have chronic mixture richness. A temporary fix would be to adjust the airflow meter to lean the mix. Then you can work on the various parts to see what's not right.

Your car has a cadillactic converter?

"catalytic" converter

a "cadillactic" converter would only be fitted to a Cadillac. (www.cadillac.com)

My car doesn't have a catalytic converter either.

FYI, a cadillac converter is what you find on cars in the part of town where the projects (low-income) housing are located.

I always seem to have trouble with my 73 passing emissions. I try to set my carbs according to the procedure and then the HC are too high. My carbs probably need to to be overhauled, but I can't afford the Ztherapy treatment (translated: my wife says it too expensive).

I recently purchased a ColorTune off the Internet for $40. Cute little toy that allows you to see into the combustion chamber. You then set the fuel/air mixture by the color of the flame. I am pretty tickled with it, and my Z passed emissions with plenty of room to spare.

I have a color tune as well and I think it is especially valuable when changing needles on the SUs. As a side note : I recently removed the PCV valve from my ballance tube to check it and found that it was leaking a little , not a great deal but if I hadent cought it , It could have caused a lean condition from the vacume leak. Just one more thing to check on especially if a vacume leak is suspected. I just soaked mine in ATF and it cleaned it up fine.

In Pennsylvania according to PENNDOT's website any car older than 1975 or 30 years is not subject to an emmissions test, therefore my '73 does not have to be emissions tested. It was surprising that a neighboring state as close as New Jersey required it.

We've discussed something like this before. I think it's still a good idea to get your engine (fuel mix and all) to be as close to spec as practically possible. It just shows your respect for the machine, your environment and others on the roadway. I'd personaly rather do without some of the smokers I've seen on the road. I bet they could've made some simple repairs to make things (better) for others.

But, until such repairs can be finished, it is nice to have the leeway to drive your car if you need to.