Chevy v8 -idle setting after rebuild?

I'd be checking for air leaks, vacuum leaks and so forth. The 284 will have a lopey idle so expect it to be "choppy" at tick over and you'll need to turn the idle speed up a bit

One thing does make me nervous is that cam is often recommended for stroker 350s like 383 etc. and talk of 10.5:1 compression minimum...

what heads, intake and carb are you running? Again recommends as far as I see for this cam are aftermarket heads, single plane intake and a 750cfm carb (based on a 355)

After the above, I'd go old school. Get a vacuum gauge on it and set the mixture and idle to get max vacuum. Then see what the vacuum is. Probably will be low (like 10 inches).

What was the static theoretical compression of the engine?

This engine is like about 8.5:1 in stock form usually.

Once you start with big cams what is more important is the cranking pressure. That is how much squeeze there is in the chamber as a long duration cam like that will hold the valves open on the compression stroke a while. This is fine if you have static compression like 12:1 (and its how some of those high compression motors get away with it) because its pushing charge either out the exhaust or as reversion back into the inlet.

Big nasty long cams like that do idle bad, just by nature of them, and the smaller the displacement of the motor the more pronounced the bad idle is.

I had the same duration cam (Comp NX284) in a 350 in my old Victor. I used Rhodes lifters to try tame it but it still idled like the thing had a HT lead off and about shook the car to bits idling in gear.

You'll never have the thing tick over like a Cadillac with a lumpy cam.

Search youtube for some examples of cars idling with hot cams like that

As Alastair explains, a wild cam reduces the compression of the engine. Because the inlet cam closes at the beginng of the compression stroke, the first part of the pistons movement doesn't compress anything. This 'valve lag' reduces the compression. Similarly the 'valve overlap' is when the exhaust closes after the inlet valve opens, this reduces the ability to draw fresh mixture in the combustion chamber. Hence the reduced vacuum.

Also, i have put in variable hydraulic lifters...

Not that i could find....

They are thrush welds. No the quad came on the car and ran fine, although I think there may have been an issue with it as it bogged down on what, but always idled fine.

Fairly sure it's a vac leak somewhere now. Will try those settings and see what I get.

So can anyone point me in the direction of the idle mixture screw on the quadrajet? Or any online guide for setting up a quad?

Magic Alistair, thanks for that!

I'm having a little idle problem at the moment too, although mine seems to be timing (wrong vacuum advance cannister) but have this pic............


Is yours the same rochester as mine? Where the throttle cables/kickdown etc are on the r/h side as you stand in front of the car, below the levers for all those is a simple idle stop screw, I'm assuming you've tried this?

If not how about the old you keep the car running at an even RPM whilst someone sprays WD40 or similar round the base of carb/inlet etc to see if the engine speed changes, my favourite way of finding an air leak.