drdave88

iTrader: (3)

I'm trying to get the carb set on my car and can't seem to get a higher vacuum reading than 12-13. Here's the rundown....
Freshly built 355 with XE268E cam
Edelbrock 600cfm
Initial timing at 10 degrees
Vacuum Advance at idle 17-18 degrees (ported vacuum)
Idle around 850rpm

I tried manifold vacuum and got closer to 15, but then my vacuum advance timing at idle was like 36! So I went back to ported vacuum. I adjusted the idle mixture screws to the highest RPM and reset RPM back to about 850. It seems to run rough anything below that RPM on ported vacuum. On manifold vacuum it seemed smoother and I could get it down to about 750. Any ideas here?

sofakingdom

iTrader: (1)

Advance the timing until it starts to ping.

Re-retard it until it just quits.

Won't necessarily be "right", but will give you a terrific idea how much BETTER the car could run if you just put down the g-d LIGHT and ignored the MARK and instead, listened to what the ENGINE is telling you about the timing IT wants.

Remember:

"If it RUNS good, it IS good."

We call this "tuning". It is a very different process from "I plucked a random number from the air that seemed good to me (I didn't ask the engine though) and pretended to set the car to that (didn't check to even see if what I THOUGHT I was setting it to was where it ACTUALLY ended up), why doesn't it run right?" You make a change; did it get better, or worse? If it got better, do it a little more. If it got worse, go back, and then a little more. Keep doing that until ANYTHING you do, makes it worse; at that point, you'll have it as good as it can be. Then AND ONLY THEN, whup out your "light" and look at your "mark", and make a note of where it is, so you can put it back in case someone of inferior intellect disturbs it for you.

pancherj

LOL! Very true. And 36 degrees advance at idle is nothing. I ended up at 52 on mine for best idle vacuum and cruising manners.

Fast355

iTrader: (2)

^^^^^What he said......MANIFOLD VACUUM for the vacuum advance, PORTED vacuum is an emissions era bandaid that quite frankly results in rough running, lazy engines that overheat at idle.

Night rider327

iTrader: (13)

About 16/17" HG vac is about the most you will pull with that cam.

Your timing is too low (retarded) An engine like that will need around 12-15* at idle w/o the vac advance.

I use full manifold vac for my vac advance units.

Then while vac gauge is still hooked up, start turning your idle mixture screws on carb, adjust screws 1 at a time looking for the highest vac reading.

91 camaro racer

iTrader: (2)

do you average your screws out after you do this? i have heard they should always be within 1/8 turn of each other.

Night rider327

iTrader: (13)

99% of the time it will end up with them being very close to each other this away. Like less than 1/8th of a turn diff.

I spend 10 to 15 min tuning the idle mix screws to get highest vac readings. Do one, rev engine a little and let it come back down and rest at idle for a few seconds then do other one, rev again, go back to the 1st screw and try to "trim" it alittle and see if vac goes up. By trim I mean a twitch of a turn, 1/32 to 1/16 of a turn. If vac goes up any then rev up again and let it come back to rest and trim the other screw.

Doing it this away will net you the best idle, smoothest running, highest vac levels

Also with the elelbrock carb, check your fuel pressure and make sure you are at 5.5 psi or less. They don't handle higher psi very well. I have a holley dead head reg on mine and limited to 5.25 psi.

Move your accel pump link rod to the top hole (guess that would look like the bottom hole on pump arm) this gives a longer throw and more pump shot.

I have not bought a new eddy carb in a few years but I know back 5,8,10 years ago they shipped them out with wrong float adjustments, even listed the wrong spec in the manual. Should be 7/16" at rest and 15/16" to 1" drop

If you have any bogs or flat spots the 1st thing to do would be to use the pink 7" hg or silver 8" hg step up springs. Most come stock with the orange 5" hg springs

91 camaro racer

iTrader: (2)

i have a holley carb. when i went to adjust the screws one at a time to get the highest vacuum. the drivers side was .5 turns out and the passenger side was 1.5 turns out.

Night rider327

iTrader: (13)

Oh, I just looked at the 1st post up top and seen edelbrock list.. Sorry, I know see you are a diff person.

Is your holley 2 or 4 corner mixture screw carb? It's alittle harder to get the 4 corner idling setup adjust with the vac gauge, still best way but it's a little tricky

If it's a 2 corner carb then something aint right at all. Maybe dirt/trash on one of the mixture screw needles or in hole. Try blowing holes with air and wiping needles clean then re try adjusting

91 camaro racer

iTrader: (2)

it is a 2 corner. i will try and clean them out