How I Passed the
Illinois Air Test
by Mike Olsen

I had to bring one of my MG’s to the test facility. Now this car was one of the last to be made before the converter was installed. It has dual SU’s, performance exhaust, a mild street cam, and no air pump. So I was concerned about passing the test. I went to a garage with an exhaust analyzer first so I could make adjustments.

The first thing I did was adjust the rocker arms so the valve overlap would no be to excessive. A little lose on the exhaust side seems to help somewhat.

In our testing it was found that mixture mostly controls CO unless you are really off. Setting the jets to .055-.050 (about 9 or 10 flats on a HS4) gave me good CO returns around 3.00.

Then We started playing with the HC’s. This seems to be the part that most cars fail at especially if you have a hot cam. Reducing ignition timing to between 0 and 5 BTDC made the largest difference. A higher idle around 1000 rpm also helped (for the test you are limited to 1100 rpm idle). My HC’s were near 400 and I needed 700 or less to pass.

Then before the test I ran a cleaner to clean out any carbon form the combustion camber.

If you pass right away there is no running up of the engine on the rollers. I’ve been told you don’t have to let the testers run your car on the rollers but I didn’t want the hassle of discussing the point if I could avoid it.

Part of the test is checking the gas cap for venting. I had been told before that my car was exempt however it had to be tested this time because of new standards. Lucky I had a spare as my old one was the vented type.

The car passed and I left with the valves written down for next time.

I hope in the near future we can change this law so this state is like the others that limit testing to 20 year old cars or less. Until then I hope this helps to give everyone a fighting chance.