Vacuum gauge tuning

[michael_cini]

I was reading the article about tuning the I6 engine with a vacuum gauge on the Classic Inlines website (http://classicinlines.com/Vacuum.asp). It is very interesting reading. I have a couple of questions though.

1) Since my car has an automatic tranny (C4) I assume that I would tune the carb using the vacuum gauge with the car in drive and idling, correct?
2) Would I also tune the ignition timing with the car in drive or put it in park and idle when adjusting timing on an automatic?
3) It's mentioned that a properly jetted engine should stall if you turn the mixture screws all the way lean on your carb. So, if the car does not die when adjusting all the way lean, then smaller jets should be installed? I would like to know more information about this one.

Thanks guys.
Michael

 

[jamyers]

For 1 and 2, you'll want the engine in Park or Neutral. The only thing you want to set with the transmission in gear is the idle speed (and carefully that).

On #3, I don't know that I completely agree...most stock or near stock carb/engines, the idle circuit isn't affected by the main jet, or at least enough to make that big a difference. Usually, if turning the mixture screw(s) all the way in doesn't kill the engine, it's because either (a) something is wrong with the mixture screw so that it isn't bottoming out and completely cutting off the fuel mix, or (b) the idle speed is set too high, so that the engine isn't running on just the idle circuit.

 

[mach1 mark]

The only way I could really get the timing adjusted correctly was to put the car in gear and adjust the timing using the vacuum gauge. So i say chalk the wheels and set the timing while the car is in gear.

 

[jamyers]

Hmm...well, an even better way is to advance it until it pings under a heavy load (like 3/4 throttle going up a hill), then back it off a couple of degrees - timing while driving being more important than timing at idle.

 

[michael_cini]

I took machImark's advice and pulled the e-brake chalked the tires and adjusted the carb idle screws in drive with my vacuum guage. What a difference, the idle is alot smoother! It's not perfect, but lots better. Thanks for the advice guys, it's much appreciated!
Michael