Holley carb Air/fuel mixture

[69'Net]

I have a 770 avenger on a 440/auto. The idle mixture screws were set on a Dyno with an air/fuel gauge. I had to send the carb back to Holley to fix a crack in the casing. Now I'm having idle issues. I tried to adjust the screws with a vac gauge but the vacuum is unresponsive when I turn them out. They only change I see from 15in is when I start screwing them in. Should I buy an air/fuel ratio gauge or am I missing something. I did this with the car in drive and the screws 2 1/2 turns out to start btw.

 

[brian6pac]

3/4 to 1 turn out and make sure your throttle plates are not open to far. .040 above the bottom of the transfer ports to start. What size cam?

 

[69'Net]

Comp cams xe274 .488/491, nothing crazy. Backfires out of the carb, dies randomly at idle. I didn't have any issues before, all that has changed is the idle mixture

 

[Ranger16]

I tried to adjust the screws with a vac gauge but the vacuum is unresponsive when I turn them out.

Does that carb have both ported and full vacuum ports (I suspect they all do) and if so, are you using the full vacuum port?

 

[Jcharger]

A/F gauges are very informative, but you don't need an A/F gauge for this - it will tell you what the A/F is at idle, but not the best setting for you. Make sure you don't have vacuum leaks and also that the butterflies are set correctly as mentioned above. Take a look at sites like http://members.tccoa.com/392bird/tuning.htm for additional information. 2 1/2 turns is more than I am used to. What vacuum did you have before with that cam. I have a step larger and am at about 10 12 inches so 15 might be OK. If it were me, I would make sure the blades are set OK (take off the carb and flip upside down), then start it check for vacuum leaks, if that was OK, I would see if it dies when the idle set screws were gently rotated in to closed, and then adjust the idle speed, set for max vacuum reading and then reset idle speed. I would then check to make sure the accelerator pump squirts as soon as the blades are touched and make sure it did not bottom out when they were all the way open. If you had it set on a dyno the main jets should be good, so the only thing you need to do is make sure the idle and transition are good.

 

[69'Net]

Ok thanks for the info. I will try that when I get time again, I'll let know how it goes.