Help please
355 sbc
iron heads, 202, 164 valves
9.5 compression
Comp Cams 280H 230 deg @ 050
dual plane intake
edelbrock 600 carb
timing 18 deg int, 36 deg total
Problem is running rich at idle and off idle stumble.
This engine needs to idle around 1000 rpms, probually because of the overlap of the cam.
Holley recommends drilling small holes in the primary throttle plates in order to be able to close the primary plates at idle with cams with a lot of overlap.
Has anyone tried this with the edelbrock carbs, did you have any luck doing this?
Thanks for any info.

You probably don't have enough vacuum at idle for the stock setup. Here's a page with a reasonably complete tuning procedure:
http://www.telusplanet.net/public/gilesij/Volvord/section_2.htm

No need to drill that Edelbrock. What is your vaccum at idle? How many turns out are the idle screws? Is it a 1405 or 1406?



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-Funk
My '67 RS (http://www.funkconsulting.com/67camaro)

The edelbrock carb is a 1405, the best vacumm reading with a guage turning the air screws is 10 inchs at idle. Idle is best around 1000 rpms.
Thanks

My first question is how is it performing at steady state crusing going down the road. Get the primaries right on this before you go screwing with springs, jets and rods. It will save you a bunch of time and repetition.

Running rich at idle is either too much idle jet/screw opening or the primaries are at play with such a high idle speed. I would expect that kind of vacuum reading by the way'

Do you have any vacuum advance on the distributor. I see you have 18 degrees of static? I really think a VA would enable you to lower the initial to 12, and boost the idle timing into the twenties which would help your idle situation and certainly the rich condition. Most of my XE274s idle very well at 850 to 900, have about 12 to 13" of vacuum, and have around 24 degrees of VA at idle. About 36 total with a 12 static.

Working with your current set up, I would set the screws out no futher than two full turns out. If it won't idle fast enough bump the mechanical idle screw up and try to achieve a 900 idle. I think with your cam that 900ish is about all you are going to get (no lower for good idle quality). If you have to come out to 2.5 turns out, this is okay, but any more is going to be toooooo rich! If the idle screws do not affect the idle then you know that the primaries are involved and you have to lower the mechanical screw that opens the throttle plates down until the idle circuit is at play.

The hesitation off idle could be a combination of either pump and/or crossover springs. I would go stronger on springs believe it or not, these carbs have a inclination to need more springs. If it gets worse go down in spring loading. Jetting may be needed to get it perfect with your cam.

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STEVE "Jack'Stands" JACK
Techical forum/links at Jack'Stands TechForums and Links (http://www.inccn.net/techforum.htm)

HOTRODSRJ
Thanks everyone for the help.
I will try to reply to your questions best I can. At steady cruise speed ( 4 speed + 3.73 gears + 26 inch tires) of around 2800 rpm at 60 mph everything seems ok. If I get down to around 2000 rpm, you can feel the motor start to jerk.
I have a MSD 6AL and MSD dist with mech advance (no vacumm advance). I have changed to lighter springs in dist to bring advance in around 1800 to 2000 rpm.
I have set initial to 24 deg before, I never had any problems with the motor cranking hard at starting hot or cold.
If I set initial to 24 deg (total goes to around 40) don't I have to change the bushings in dist to limit total to 36 deg no matter what the initial is?
The idle screws now are about 4 turns out, setting them with vacumm gauge, this gives me the highest reading of 10 inch.
Idle screws seem to respond to adjustment ok, but less than 4 turns idle gets more lumpy and off idle stumble gets worse, plus vacumm reading goes down.
Off idle bog and a mushy throttle felling seem to be worst problem.
Please explain more about pump and or crossover springs.
Thanks again