timmah22

what's a good idle vacuum reading at idle for the L-79? Looked everywhere and can't get a good average answer.

On the idle question, since i installed a holley heat shield....starts up fine when dead cold...Holley 4160 with divorced choke. No heat riser... tap accel pedal for full choke and fast idle cam puts rpm to 1200-1300 RPM. After warming up for 5 minutes or so, if i tap on the gas it drops to 600-700 and struggles till its up to full operating temp (850 rpm). Same thing happens if i start it up after parked for a couple hours and then started...low rpm till hot.

Do I need to adjust the choke rod/fast idle cam? fuel issue 93 shell? Carb mixture has been adjusted to best vacuum and running at 10 btdc

Tampa Jerry

As long as you have a stock cam, a steady 17" is ideal. There are a few good websites that show vacuum readings with various engine problems. Google the topic. Jerry

timmah22

Thanks Jerry...I have researced several guides on vacuum indications.....normal on most was showing 20-22". Nothing specific on a stock L-79. I'm having no issues with vacuum. Just choke/fast idle cam/ idle problems when not at full temp.

Donny Brass

I struggle to get to 16 14 seems to be normal

over course, my L-79 is slightly above average

65 vette dude

Mine runs 15-16 vacuum, and I idle at 800rpm. My start up pretty much mirrors yours. She struggles to idle until she reaches about 160 degrees.

IGO200

I don't have the link handy, but JohnZ has an excellent article on setting the divorced choke setup. I followed his procedure and mine starts, warms and runs just as it should.

MikeM

It's been a long time since I checked mine but I believe it was about 17" at maybe 750 rpm with about 25 or so degrees of timing thrown in.

If all you're getting is 14, your engine is either shot or you have modified it outside of stock spec!

AZDoug

My car was in the 16-17" range, but it has been so long, i can't tell you for sure if that was with the vac advance hooked up, or not. I believe it was with vac adv operating.

Doug

AZDoug

Or not *pure* stock....

Didja cheat on that cam grind, a bit???

Doug

Jebbysan

I run 14-15 inches.....idle at 900 because the 3.23 can be hard to slip out of the hole around town.

Jebby

JohnZ

Here's a link to that article:

http://www.lbfun.com/warehouse/tech_..._Idle_Tech.pdf

Donny Brass

Most of the vacuum advance is locked out

Reulandjr

My 79 pulls about 15 vacuum and has cold start issues. I checked the vacuum on the fast idle can and there is no vacuum there. Traced back the line and it connects to the speedometer connection on the drivers side fender? What's up with that? This thing pulls vacuum straight from the manifold and has plenty of vacuum coming in but nothing going out. Anyone know what this is and how it works? It seems that my cold start issue is because the idle advance isn't kicking in....help?

62Jeff

There is no stock corvette configuration that puts a speedometer cable on the fender. Do you have pictures?

MelWff

Your question belongs on the C3 forum this is C2. Your car is not set up for vacuum advance at idle if it is stock.

62Jeff

Ack, good point. I overlooked that detail of his post.

timmah22

Thanks JohnZ for the article, It took me a minute to figure out to turn the screwdriver counterclockwise (like tightenig a screw) on the tang to increase RPM. I thought you had to bend the tang and use the screwdriver like a prybar! lolworks great now!