I did a search for tuning instructions and tips, but didn't find what I was looking for exactly. I decided to mess around with a vacuum gage to try and see if my idle air/fuel was set properly. Warmed the engine up to around operating temp. Hooked the vac gage up to the big center port on the carb (I believe this is manifold pressure) and started the truck. Idled fine, right at 700 rpm. Got out and looked at the vac gage. It was right around 15 inches. I started playing with the two screws in front of the carb as described by the Edelbrock manual and also the previous posts I have read on here. I checked each one to see how many turns the screws were out from the closed position, about 1.5 turns. I then started backing out one screw while watching the vac gage. It barely came up any at all. No change in engine rpm. I kept backing it out till I got to 6 turns and said "There's no way this is right" and screwed it back to about 3 turns out. Backed out the other screw to 3 turns with no change in vacuum pressure or rpm. From everything I have read, the rpms will come up about 50 and the vac pressure will rise. If you back the screws out too far, it starts to choke out the engine. Why did I not see any of these things really? I don't think I have any vac leaks as the gage was pretty steady, not really bouncing around. I finally settled on 2.5 turns out, then adjusted the idle to 600 rpm. Climbed in the truck and gave it some gas. Bumped it kind of hard and it fell on its face, almost like it was flooding. After a couple of revs, noticed rpms dropped about 50 and walked to the front of the truck. Sounded like a rocker arm coming loose on the passenger side head. I'll have to take a look at that this weekend. One final question, what rpm is the idle supposed to be set at when checking all of this? I noticed in previous posts they were saying 20", but I was only pulling 15. When I dropped rpms to 600 the vac pressure dropped to about 13. Sorry for the rambling mess, just kind of frustrated.

 

Timing first then carburetor , check for vacuum leaks

 

Hotstuff, the timing is 10 deg BTDC with aftermarket balancer.

 

Update. Checked the timing again this afternoon (vacuum advance plugged) and it was almost 10 deg AFTER top dead. Good call on that one. Loosened up the dizzy and moved it to 10 before top dead. Backed out the idle set screw on the Edelbrock, as advancing timing raised rpms. Went to hook the vac advance back up and the engine surged as soon as I hooked it up. Threw the timing light on it and it was running 20 deg before top dead and jumped to 900 rpm from 600 unhooked. Why so much vacuum at idle from ported vacuum off the carb? My understanding is the ported vac works off the "butterflies" on the carb, which are partially controlled by the idle adjust screw which I closed more when I adjusted the idle. I took it for a test drive and it ran great I thought. Any thoughts?

 

Ported vacuum port is above the throttle blades , on edelbrock its on the left facing the carb , full time vacuum below the throttle blades on the right . Are you sure you are on the correct port ?

 

Yes, my vacuum for distributor is coming off the left port. Double checked the owners manual to be sure.

 

If you are getting vacuum off the ported port at idle the throttle blades are open to far , try backing the idle off a bit

 

That's what I thought, and I tried backing the idle adjust screw out to lower the idle and close the butterflies. It was still pulling vacuum like crazy. This is at 10 deg BTDC. I could try bumping up the timing but worried about going too far and getting detonation and overheating. Motor is a 460 with 9.5:1 compression running 87 octane gas. How far do you think I could go with timing before I have these issues?

 

with vacuum gauge on ported port , start backing the timing up 2 degrees at a time while adjusting the idle screw to the proper rpm find what the motor likes . its a test, keep going until you find the happy spot