Tuning Edelbrock 4 Barrel

[Mac]

Still trying to tweak the most out of my carb tune. It's running pretty well but I'm trying to decipher readings I'm getting from the in-cab (non-wide band) Autometer A/F Ratio gauge.
It's showing just a little too rich at steady cruise but when I give it a slight bit more throttle it goes leaner for a moment, which seems the reverse of what would expect with the accelerator pump just having been engaged.
I'm wondering if that slight, momentary drop in vacuum signal is playing a roll (stepup springs?)

Specs:
`63 Chevy C-10
Roller GM 5.0 w/ LT1 cam
Edel. Perf. Intake w/ 1" phenolic spacer
Edel 500cfm 4bbl w/ non functioning man. choke
Carter Elect. Fuel Pump
Holley press. regulator set at 4.5 lbs
Home fabbed cold air snorkel from core support (now that cooler weather is on us it's running generally leaner)
Block Huggers into single 3" exhaust

TIA

[wayne petty]

got a vacuum gauge you could mount next to the AF display ... so you can see what both are doing ...

i would like you to count the turns in on your idle mixture screws... then remove them.. give each a quick blast of carb cleaner followed instantly by a blast of compressed air..   repeat 3 times each side..

this will usually blow any debris out of the idle air bleeds and the Idle feed restriction.

reset your idle mixture screw using a vacuum gauge and getting the throttle plate as far closed as possible..

why..  the idle air bleeds are constantly pulling air in.. this includes dust .. that can clog the idle air bleeds or idle feed restriction..

by posting these PB links with the tail original it opens in a page hopefully without ads and crud...  let me know if you get the image only. i don't know where my originals are..


http://i1207.photobucket.com/albums/bb476/waynep712/waynep712%20carb%20album/AFB_AVS_primaryboosterdiagram_zpse535929c.jpg~original


http://i1207.photobucket.com/albums/bb476/waynep712/AFB_AVS_airbleeds_zps9b83323f.jpg~original


i wish i had a modified cover for the metering rod pistons with a guide tube and a dipstick tube.. so i could see at what manifold vacuum the springs would over power the vacuum...  using something like a spray can straw section as a pop up indicator..

http://i1207.photobucket.com/albums/bb476/waynep712/waynep712%20carb%20album/afb_primary_rodspringdiagram_zpsf9b6c3da.jpg~original

i would think that at 2200 to 2500 rpms with a steady throttle on a level road the primary springs would be fully seated.  easy to tell.. by knowing what your vacuum readings are..

this would be so that as soon as you tip deeper into the throttle the springs overcome the slight drop in manifold vacuum and increase your fuel feed to the primary booster..

this is how quadrajets work and get great mileage..

quadrajets have the APT adjustment and limit how far down the springs can pull the tapered quadrajet primary metering rods into the primary main jets..  so coming into the primary mains from only on the idle transition the primary does not go lean..   with edelbrocks you have to change jetting .. metering rods and springs to get the part way thru idle transition and main operation to not go lean...

do you have a timing light.. and a video camera.. you might be able to aim those down the primary throat and see at what speed as the person pushing on the gas pedal is moving it 100 RPMS at a timing and holding it there then moving to the next 100 higher.  going up and then down from 2800.. to see when the primary drops out..  runs only on the idle transition.

some day.. i will make it the 18 miles over to edelbrock and see if i can chat them up about creating pairs of primary booster with different sized idle feed restrictions already pressed in... so one set could be used with 5.0 motors.. the sets with the carbs are probably set for 5.7 to 383 motors.. another set for 427.. a set for 454/460 motors and one for 500 inch motors..  so its quick and easy to change the primary boosters to change the idle feed restriction and if it does not work .. put back the smaller size..

might even be nice to have a few sets of the big diameter/block the air flow versions to make conventional AVB/AVS sizes into the 400 CFM versions..

[idrivejunk]

Step up springs are everything... on an EPS carb. If you don't have the assortment, its WELL worth the few bucks. Sounds to me as if a slightly stronger spring is needed, if everything else is tip-top and you just get a lean moment before the rods can fully react to throttle input. Getting the right step-up springs in there might allow trimming some cruise mode fat.

[Mac]

Wayne, as usual I have some assignments to prepare before the next class. All good stuff...you're the best.

idrivejunk, you make a good point and I'd then need to change rods and/or jets as now it's showing fat in cruise and only going to the middle of the lean range of the gauge when I tip in a little. Oh, and it goes into the lean range when I'm pulling a grade also, which seems to bare out the mani. vacuum drop coincidence too.
I have changed rods and jets to leaner already from stock. But if it results (as it well might) in better MPG it'll be worth it.
I don't remember if I dropped 1 stage or more when I made the change to the primaries...and I didn't record what I did. I was bad in school with homework, too.  :oops: You didn't hear that, Wayne.

[idrivejunk]

At least by having a gauge you can quantify results and that beats butt dyno any day. The smaller CID tuning may present issues that don't sound like normal power-hungry ones, and no worries because the stock config is spec'ed in the manual so returning to stock default mild 350 as-boxed tune is a snap. Driveability / economy lies in that $8 step-up spring pack. You're right too, Mac, about maybe having to re-change components as you zero in on proper metering. Once you're done though, I love how the EPS lets you just drive forever and touch nothing. Rock-steady tune if kept clean!

[wayne petty]

FYI..

i had a sunpro AF ratio gauge.. and a vacuum gauge...

they are missing now..

i mounted them upside down in a double gauge bracket..

mounted the gauge bracket on a piece of carpet backing side toward the gauge bracket so they could be set on the dashboard top without scratching..

with this set up.. a vacuum hose to the gauge.. a pair of wires from the oxygen sensor.  and a pair of wires to a accessory plug to plug into the lighter power..  this makes it really easily removed.. without mounting or drilling a bunch of holes.

i don't know what happened to the first one i built.. it walked away from the pile of stuff on top of my tool box..