Notice on your Dec 17 test you scored a 5.51%CO at idle and the cutoff is 5.45? If the numbers were reversed you'd be pissed. By changing your engine size, you wouldn't fail in that scenario -- although the engine size only affects the HC readings. Also, the weight of your car is a factor in determining your cutoffs. A Super Beetle will have different cutoffs than a Standard Beetle of the same year even though the engines are identical. Changing your engine size gains you a tiny amount of headroom, and its completely legit, so why wouldn't you do it?
How does it drive when adjusted to make aircare happy? You say it idles higher and smoother when you give it more fuel, but the CO readings say that shouldn't happen. I would look at other causes. It shouldn't take 5+% CO to run good. It may be that you need to go bigger on the idle jet. Maybe a 57. It could be that your rich idle setting is compensating for a near flat spot just off idle. By Upping the idle jet you will be able to lean out the idle setting. This is what happend to me last year. In my current 40 Dellortos, I used a 57 idle jet. My driving CO was .5% (on the lean side) And my idle CO was around 6% (very rich) But that's the settings that made it drive really good. So what I did was to go up on the idle jet to a 60, and wind in the mixture screws. I got the driving CO up to 2.3%, and the idle down to 3.9%. Right now in this cold crappy weather, it drives almost like a modern FI engine, better than it did before.
I installed my old 2 liter in '93. It was 78x90, 40x35 040 heads ported, 8:1, Engle W-125 cam, 1 5/8\" exh. and originally with 40IDFs. In the spring, I was working at trying to get through on CO, but couldn't make it. At that time no one knew that it was the idle jet that affected your driven CO, so I was mistakenly changing the main jet. I went down to a 100 from a 115, and all that happened was it drove like crap at the upper RPMs. Finally we figured out that it was the idle jet that affects CO, so by going from a 50 to a 47, I passed the numbers. Keep in mind my car is a 75, so I have to meet the numbers for a car that was originally FI. Where you are allowed 1052ppm of HC at idle, I have to beat 480. I had been going out to Mission regularly during all the changes trying to pass, and when I had the final passing setup, that same setup without any adjustments netted my best ET I ever made with that engine combo. It was 14.61@87mph. That is with my heavy car (2000lbs even down the track with me in it). Then a couple of years later, I ported some IDA manifolds and worked on them. I think it was on my second attempt that I passed with 48s on it. In that state it went 14.31@92.5mph at Mission. I even taped the inspection report to my quarter window that year at the show in Coquitlam. When I hear someone bitching about not being able to pass with their 50something Bug and tiny engine, I've got no sympathy for them, hey, I have to work a lot harder, with a bigger, wilder engine, and I made it, so why can't you?
You are absolutely right about most people's perception that it must run like crap to pass. This is because there are ways to beat the numbers with an engine that runs like crap, and everytime someone does this successfully, they have proven in their mind that it is true. How many modern cars run like crap to generate the microscopic readings? The ones that perpetuate the \"has to run like crap\" myth are just demonstrating their ignorance of emissions. I have to admit its a real problem for DIY'rs like us to be able to do it right, how many people have the $$$$ to buy a 5 gas exhaust analyzer to put in our home garage? Ten years ago I started using an O2 sensor. It was very helpfull, like many have discovered today. I've just found a cheap at home type CO meter. For $150, you can get a real gas analyzer, but it only measures CO. Unlike an O2 sensor, which just measures the presence or absence of O2, the Gunsen gas tester measures actual CO, just like aircare.
Geoff, do I get the record for the longest post ever?
