Can anybody give me some tips to passing Arizona's I/M 240 emissions
testing. I have a 74 Ford F-100 4X4, 360 converted to 390, with an
aftermarket Q-jet carb with Edlebrack intake manifold. The
conventional ignition was converted to a late 70's Ford electronic
system. The carb has been de-jetted to the point I don't think I can
get smaller jets. The rebuilt engine has apx 40-50,000 miles of use.
Over all it runs great, the problem is with the Co. I need to lower it
just a bit to pass. I cheated last year, getting by on the re-test by
going through in 4 wheel low. This year the inspector was wise, moved
it back into 2wl high and I failed on the high speed test.

Any suggestions are appreciated. I just need to get the Co level down
just slightly to pass. I would really like to get it through
legitimately without red-lining the engine in 4wl low. A local garage
lowered the Co levels once by changing the park plug gap.
Unfortunately I can't recall if he increased or decreased the gap.
I've heard various gasoline additives will lower the Co levels a bit,
but I don't really know if I'm relying on sound advice or an urban
legend.