Re: Project SBC Failed Smog - Smog Guru input?
You are close!
It's just a teeny bit too lean. Retarding the timing a couple degrees might help.
It's lean enough that the flame goes out in the chamber a little too early, leaving a small amount of raw gas.
Richening the mixture screws slightly MIGHT help, but may cause you to fail at low speed.
If the gas has been in the tank a long time - change it. You might have to drain it or drive it a bit.
Change the plugs as recommended - plats are terrible in engines that weren't designed for them. Use STOCK plugs called out for that ENGINE, not the for ignition or anything else.
Set the gaps SLIGHTLY on the wide side. (The slightly wider gap ignites better at lower/mid range speeds. Not so good for high R's though.) Regap after you pass. The stock plugs - the ones the HEADS were designed around - have the correct reach and indexing - very important for emissions. The plats are too "one size fits all."
Then make sure the gas is no older than a week (the addatives they put in evaporate fast.)
And - the trick - that morning - add a pint of DENATURED ALCOHOL to the tank. Same stuff as the "garanteed to pass" stuff. Not rubbing alcohol, not Vodka (put that in you.) DENATURED ALCOHOL is available in hardware and paint stores - where they keep the laquer thinner. 99 cents or so.
Warm it up, make sure the alcohol has had a chance to mix in.
If it fails again at high speed, but CO at low speed is way lower than the cut point - try richening the idle mixture screws just a tad. That might be just enough to get by.
BTW -- I think paint only helps if it's passionate pink with orange, green, and purple stripes - the ref passes it quickly so he doesn't have to keep looking at it!