Wouldn't the idle timing that pulls the most vacuum produce the lowest HC (most efficient burn)?

 

You'd think so, but no. I get the highest manifold vacuum 38 deg, the best idle quality at 28 deg, and decreasing HC as low as I dare go.

With the retarded timing it causes a huge amount of exhaust heat. I melted my brake booster and smoked a mount!

 

Where are you located?? I had problems passing last year, and raising the idle to ~1250-1300 really helped. I took the car to a shop and put it on a gas analyzer and at normal idle ~850 - 900 the HC's would shoot way up and this was with a cat on the car. If gave it a little throttle to pull the rpms up to 1200 - 1300 the HC's would drop drastically. Between me upping the idle and running some denatured alcohol it passed with numbers better than the last time when it was stock.

-Tony

 

Our testing sites require the RPM to be under 1050 here in washington. I'd bet if I could idle at 1500, it'd pass!

They plug into the cig lighter to measure your rpm. I'm sure I could build a circuit with a 1000 Hz noise source, but I'll put cats in instead :-)