help holley 4053 Z28 carb not idleing right

[svtrich]

I put 72 jets in the pri.76 in the sec. Im not running the 3030 cam but it dosent idle right.i adjusted the mixture screws but still it isnt right.still idles around 1000rpms
                     Rich

[Stingr69]

Is the engine new to you or did something get changed?

The float setting needs to be checked on the car first. You want fuel to just barely dribble out the sight holes then lock it down.

I set the idle speed screw with the carb off the engine. Turn it over and set the screw so the amount of the "slot" exposed looks like a square.

Set the mixture screws at 1.5 turns out from lightly seated then reinstall the carb.

Verify the timing is right and you should be very close.

-Mark.

[jonboy1216]

idle mixture screws can only be set correctly with a tach or vacuum gauge. with gauge or tach hooked up turn idle screw all the way in .then turn out slowly til the gauge or tach reads the highest number then stop and go to the other idle screw and repeat. and remember that one side can have a different setting. as in drivers side can be 1 turn out and pass side can be 3 turns out because each screw controls one idle circuit.hope this helps

[JohnZ]

with gauge or tach hooked up turn idle screw all the way in .then turn out slowly til the gauge or tach reads the highest number then stop and go to the other idle screw and repeat.

With the idle mixture screw turned all the way in, it won't run at all. A better starting point is where it's already running, or 1-1/2 turns out from lightly seated. Work back and forth between the two screws to achieve the highest steady vacuum reading, tweaking the idle speed as you go.

[JohnZ]

I put 72 jets in the pri.76 in the sec. Im not running the 3030 cam but it dosent idle right.i adjusted the mixture screws but still it isnt right.still idles around 1000rpms
                     Rich

What cam are you running? The "30-30" typically likes a 900-950 rpm idle speed.

[jonboy1216]

if you turn slowly in it will stay running. there is no set # of turns on the idle screws to start or end with that is for people who dont know how to tune a carb

[dutch]

For what it is worth - what I have learned the hard way regarding Holleys is as follows...

 With a carb that big (for engine size) you have lots of juice with those jet sizes - I would guess 68's and 72's would probably be much better in a final sense... but that said, and as John mentioned, a 1-1 1/2 open point for the needles is about right for primary adjustment and initial starting point.
Once you get it warmed up and get the float levels correct (very important esp. the float levels as mentioned previously) it should respond to needle changes if all else is well internally in the carb - and it should start to die out pretty much anywhere under 3/4 -1/2 turn in on the needles (again if all else up to snuff).
If it continues to idle the same as you turn the needles in or out then you probably have a power valve problem in either it is way off size-wise, or is blown out and that is why the response isn't there... Too far out of range or blown will usually be accompanied with enough fumes at idle in an enclosed area to make your eyes water to confirm this!
All of this is prefaced on the assumption that the cam you are using is pretty big and also similar to a 30-30 type but not something radically different which then throws a lot of any advice out the window as different cams create much different vacuum signals and therefore mixture, jetting, and power valve requirements.
If you have the butterflies open too much to keep the idle up to prevent it from stalling out, often the transition slots will often get uncovered too much as mentioned also and it will make any needle valve adjustments futile. This quite often occurs again when the carb is too big for the displacement, vacuum signal, or compression ratio, and the only real crutch for this is to adjust the secondary butterflies stops a bit open to get more air, to allow closure of the primary butterflies sufficiently to cover the transition slot which will help make the idle mixture screws somewhat more responsive again and get that part of the adjustment equation working hopefully... - failing that drilling a small (1/16" or so) hole in the front side of the primary butterflies can be of help to aid in getting more air in at a somewhat decent idle speed but this type of thing should only be used as a last resort and when all else fails...

Good luck - Randy   

[GaryL]

I had a similar problem when the engine was new. I put this 302 together buying dated parts. The carb I bought, that looked good, had a problem. One of the idle outlet ports was plugged. It was trying to idle on one side only. Since then the front metering block was replaced. I can not get this big old 780 to idle rich, so I think I need some idle feed restrictor work done by a competant carb rebuilder. Just some food for thought.

By the way #72 front jets would be right for a stock 302 with the 30-30 cam. That is a normal tune for that engine. They produce a surge free cruise speed. They have nothing to do with idling.

[Jerry@CHP]

Distributor is also very important.  Total centrifical shouold be in by about 2600 rpm.  Factory curve also have to be shortened.  If not, the car will not idle right.  The carb and dist have to work in concert or it's not going to run right. 

Jerry

[GI JOE]

 

This method everyone is talking about is known as the "Lean Drop or Lean Roll Method."  You are basically finding the best Air/Fuel mixture (not to lean, not to rich) using a vacuum and tachometer gauges plus small screw driver...  What has been wrote is correct...(i.e jonboy12, others)... if you can set your timing you can do this... also don't forget the fast idle adjustment... in case this is why you're at 1K rpm... Good luck  and let us all know how it turns out...   

PS I would also recommend you Google "Holley carb Lean Drop" and or purchase the Peterson's Holley Carburetor book....

http://www.chevyhiperformance.com/howto/45638/index.html