69 Z/28 idle problem - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

LinkBack Thread Tools Display Modes
post #1 of 6 (permalink) Old Jul 15th, 02, 03:06 PM Thread Starter
Join Date: Jul 2002
Location: Southbury, CT
Posts: 16

I'll apologize in advance if this has been asked a thousand times, but I am new to the site...

I have a bone stock 69 Z/28 with the 302DZ. Engine was last rebuilt in mid 80's and has seen little mileage since that time. The car generally starts right up and runs well.

That being said, I cannot get the car to idle @ 900 rpm without it dying at stoplights or when you turn the steering wheel hard. The solution to this was to turn up the idle speed to about 2000rpm...not ideal. I have checked the timing, which is supposed to be 4btdc @ "proper idle" and it seems close. I have also played around with the mixture screws, but lacked a vacuum guage and was not able to get an accurate read off the dash tach...ended leaving them at the approximate setting of three turns out from full in. I haven't found any vacuum leaks, although I am not 100% certain.

If I don't figure this out, I am going to just start taking stuff apart and soon I'll be in for a full rebuild and spending money I shouldn't be. What do you think????
Jdawg is offline  
Sponsored Links
post #2 of 6 (permalink) Old Jul 15th, 02, 03:26 PM
Join Date: Mar 2002
Location: pocatello idaho usa
Posts: 21
take the air cleaner off and look down the top of it into the primary side of carb
in the front you will see 4 little holes 2 on left 2 on the right take a fine piece of wire and clean these out they are thye air passage for a holley carb at idle if this dont work try changing the power valve you may have blown it if car has backfired
454bruce is offline  
post #3 of 6 (permalink) Old Jul 19th, 02, 10:59 AM
Team Member
JohnZ's Avatar
Join Date: Sep 2000
Location: Washington, Michigan USA
Posts: 7,728
You need to get a vacuum gauge so you can properly adjust the idle mixture for highest steady vacuum; on my bone-stock '69Z it's usually about 1-1/2 to 2 turns from lightly seated.

If it has sat for long periods of time, you probably have some gum and varnish that's formed in the idle system as well, which would explain having to go to three turns out to get it to idle - probably time for a thorough carb rebuild and cleaning. Get the correct genuine Holley rebuild kit - don't even bother with any of the generic parts-store rebuild kits.

'69 Z28 Fathom Green
JohnZ is offline  
post #4 of 6 (permalink) Old Jul 21st, 02, 06:07 PM
Senior Tech
Join Date: Mar 2002
Location: San Francisco, CA 94114
Posts: 103

What kind of vacuum readings do you see on yours at idle? On mine, with the idle screws at 1.5 turns from seat, I get about 5.5 inches of vacuum. If I go leaner (about 3/4 turn from seat) and raise the idle speed, I get about 8 inches of vacuum at 1,000 rpm. I also have a slight off-idle stumble with this setting. I am into the transition circuit?
NeilB is offline  
post #5 of 6 (permalink) Old Jul 22nd, 02, 02:28 PM
Senior Tech
Join Date: Feb 2002
Location: LR AR
Posts: 2,372
I have to say I have the stumble at tip in as well on my new 302. I am sure it can be tuned out and when I do figure it out, I will post my findings. I suspect the vacuum advance is backing off as the throttle is cracked and before the RPM's come up, it tries to die. This is leading me back to try setting it up with ported advance. That is not the best setup for cool running at idle but it would be nice for the engine to actualy take off when the throttle is gently opened as it does using ported advance. It might also be idling on the curve but I have not had time in a few weeks to look into it. Maybe the parts will arrive tomorrow I hope.

stingr69 is offline  
post #6 of 6 (permalink) Old Jul 23rd, 02, 06:41 AM
Senior Tech
Join Date: Feb 2002
Location: LR AR
Posts: 2,372
As for an update, my distributor IS in fact idling "on the curve" so the first thing I will do is braze the advance slot up so I have about 24 degrees in the centrifugal advance. I have too much right now and the advance starts too early compounding the problem. The throttle gets cracked, the manifold vacuum drops a bit causing the vacuum advance to back off which lowers the engine speed which reduces the advance some more which basicaly, is like a house of cards. The RPM drops and can not come back on its own and within a few moments, it dies.

Jdawg, if you have a totaly stock spec DZ 302 distributor hooked up to ported vaccum, you need to read some of my other posts on the subject. The jury may be still out on the ported vs manifold advance but nobody will tell you the stock DZ 302 curve is the way to go. The emissions calibration will make the car run much worse than it would with a proper curve. If you look at some of the non-emission engines built with almost all the same parts, cam and specs, the 64-65 Corvette SHP 327/365 HP motors are almost exactly the same as a DZ 302 with .25 longer stroke. The ignition setup for those engines is WAY different because they did not have to worry about emissions back then. The distributor setup and curve is WAY better IMHO as compared to the stock DZ setup. I hope to be able to modify my advance today or tomorrow and test out the new curve and report back as time allows. I am working on preparing for a few job interviews next week so garage time comes second.

stingr69 is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome