eddp

I'm trying to dial in my AVS2. When it comes to metering rod springs, am I understanding this correctly?
The lighter the spring, the longer vacuum will hold the rod down in the jet. Example: the yellow spring is 4"hg. So vacuum will hold it in the jet until vacuum drops to 4"?
The heavier the spring, the sooner the rod will lift out of the jet. Example: Pink spring is 7"hg. So at 7" the rod will lift out.
Am I correct that the sooner the rod lifts, the more rich and the later, the more lean? As the rpm increases, the vacuum drops, so the lighter spring would keep it lean until higher rpm to wot?
I already went one rod lean without a jet change.

Haggisbash

Yes you are correct. As you have probably noticed the rods have two tapers on them, one that meters the fuel when the rod is down and another when it is up. Remember that the spring rating is not a switch but just the starting point where the rod moves to the second taper.
It's not the rpm so much as the loading on the engine that makes the vacuum drop.
The tuning guide that comes with an AVS2 is very helpful to get a good set up but the key is determining what air fuel ratio you have with a particular combination of jets, rods and springs.

eddp

What im hoping to do with the springs is stretch the transition from lean to rich. I have the pink 7hg springs in presently, which I think allow the rod to lift when vacuum drops to 7hg. I think if I put the yellow spring in, it will hold the rod a little longer until vacuum drops to 4hg.
I went one rod lean with no jet change.
I do a lot of stop and go in town driving, so a lot of light throttle driving. I'm hoping to get a little bump on milage.

Haggisbash

Do you have a vacuum gauge? If an automatic what is your idle vacuum reading in drive while stationary?

eddp

I have a gauge. I need to get someone on the brake and check that. The Edelbrock tech told me to check vacuum at idle in Park. I'm getting 15hg at 750 rpm with a 2.18/2,24 @ 50 Comp cam.

jim-81

What engine and what carb? (650, 800)

jim-81

Here is the Edelbrock tuning manual if you don't have it. Pretty good explanation of how it works in there.

Ugh nevermind it won't let me attach a PDF.

jim-81

good article here:

https://www.hotrod.com/articles/tuni...vs-carburetor/

Rescue Rogers

I did a bunch of tuning and plug reading dialing in an old edelbrock and a vacuum gauge. It takes alot of running down the block and coming back and swapping stuff. Its doable and the graph helps alot once you understand where you are on the graph and where you need to go. Figuring out where you are is the hard part. I would clean the plugs then go for a long cruise never getting above part throttle then reading the plugs to see if they were rich or lean.


Once I got my AFR gauge it was a lot easier. I dialed in my quadrajet pretty fast without having to much guessing at all. I would just look at it at idle and adjust the idle set screws. Take it for an easy cruise to see what was happening at the transitions. And of course WOT throttle was pretty easy on the highway staying in a lower gear for the higher RPM. It makes life so easy

Haggisbash

I agree with Rescue but would go for a cruise with the vacuum gauge attached where I could see it. I think if you are pulling 15" of vacuum at idle you will be surprised at how fast you will be going on a flat road before the vac drops below even the 7" rated spring. A lot of what you need to tune will be idle mixture screws, these have an effect on the running well above the idle rpm. I notice with an A/F ratio meter that even an 1/8 turn on these makes a big difference to the A/F ratio (at least it does on my 350).

Jebbysan

I talked to you about this on FB.
I believe something else is wrong as changing rods has no effect.......at 15" hg the pistons should be all the way down in the bores at idle with the pink spring.
Where is your timing at? You have to have correct timing before you even think about tuning these carbs......
What intake manifold are you running?

Jebby

eddp

Engine is running smoothly, temp is very good. Plugs are just a little rich looking.
A lot of in town, soft throttle stop and go driving. I think its just a tad rich and I think its transitioning a bit to soon.

Haggisbash

Clean the easiest plug for you to get at, run the car around exactly the same as you describe you have been then pull over and immediately turn off the motor. As soon as it cools enough to dp so pull out that plug and take a good close up pic of the business end and post it so we can see what it's like. Are you checking for the transition point with a vac gauge under driving conditions? Else my only suggestion would be to get an A/F ratio meter so you can really "see" what is going on. Did you follow the Edelbrock tuning instructions for idle etc that came with the carb?

eddp

Followed the Edelbrock FA directions. Don't have the vacuum gauge at run set up, just park idle. Debating FA gauge.

Rescue Rogers

I have an AEM wide band gauge mounted on my A pillar...I love it for engine tuning and just monitoring as I roll down the highway