Author Topic: 69/302 idle problem  (Read 6752 times)

bobs69z

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69/302 idle problem
« on: April 24, 2020, 09:12:36 PM »
Looking for alittle help. My 69z,with original engine and carb won't idle. I have had the carb rebuilt and looked at twice form Eric's carb shop. Distributor has been redone by Camaro Hi Performance. And engine was recently rebuilt, before I bought it.  I have set total timing @36. Car starts fine. I can get it to idle around 1500 rpms for about 10/15 mins. then it slowly dies. If i turn idle down, it wont idle at all.  Ive checked float bowls and set air mixture. Ive also checked for vacuum leaks around carb and intake manifold. Any ideas would be appreciated....Thanks Bob
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BobH11

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Re: 69/302 idle problem
« Reply #1 on: April 24, 2020, 09:20:19 PM »
Check your vacuum, make sure you have the right power valve and it’s not leaking.

crossboss

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Re: 69/302 idle problem
« Reply #2 on: April 24, 2020, 09:20:49 PM »
Check the basics…again. Just because it was re-built, that does not mean it was done correctly/properly. My suggestion would be to start the engine, and then cup your hands over the carb. IF it dies, there is most likely no vacuum leaks. Don't rule out a bad plug(s)/wire(s), and the fuel pump too. That said, IF you have a known working carb, make a swap and see what happens.
Just another T/A fanatic. Current lifelong projects:
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bobs69z

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Re: 69/302 idle problem
« Reply #3 on: April 24, 2020, 09:44:46 PM »
I was thinking fuel pump. But there is still fuel in the float bowls when engine dies. I disconnected fuel pump and put a gauge on it towards pump. On start up had no vacuum on gauge then rose after about 5 secs. to 14.  Does that sound right?
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bobs69z

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Re: 69/302 idle problem
« Reply #4 on: April 24, 2020, 09:48:26 PM »
BobH1  Nothing leaking around carb. Is there a way to check vacuum with gauge? And where would I check on carb?
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uscrichter

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Re: 69/302 idle problem
« Reply #5 on: April 24, 2020, 10:02:20 PM »
Could be some debris in the carb that are clogging, I have had this problem and took apart my carb only to find a small piece of rubber seal that restricted fuel at idle, it doesn't take much to clog those ports.

BobH11

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Re: 69/302 idle problem
« Reply #6 on: April 24, 2020, 10:24:29 PM »
Did you set the idle mixture with a vacuum gauge? The power valve is internal, wouldn’t leak to the outside.

firstgenaddict

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Re: 69/302 idle problem
« Reply #7 on: April 24, 2020, 11:49:40 PM »
I was encountering the same issue, trail off and die...
Try opening your idle mixture screws 1/2 to 1 full turn each.
I had the mixture set as per the specs and was having the same problem would taper off and die out...
I replaced the fuel pump and rubber hoses then still couldn't figure it out, finally I was messing around and for the heck of it I backed out the mixture screws in my mind thinking it would be WAY too rich, but then the idle stayed even with little dithering - now I have it idling at 750-800 RPM's with 15" vacuum.
 
After running for few hundred miles, I pulled a couple of plugs and now it has a nice tan ceramic insulator. 
FWIW I do run 110 Sunoco or 100 LL aviation.
James
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bobs69z

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Re: 69/302 idle problem
« Reply #8 on: April 24, 2020, 11:58:04 PM »
I didn’t use a gauge. Wasn’t sure how to use it. Set it per specs. I’ll try backing screws out.
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Maxsg1973

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Re: 69/302 idle problem
« Reply #9 on: April 25, 2020, 01:09:44 AM »
Do a cylinder leak down test to make sure you don't have any cylinder charge issues. You may need to check the valve clearance if you have solid lifters. It might be a good idea to take it to someone who is proficient with an ignition scope.  A good tech with a scope should be able to get to the bottom of it quickly.

TODD

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Re: 69/302 idle problem
« Reply #10 on: April 25, 2020, 04:37:23 AM »
Is it rich at idle? Even after Eric did my carb I had to open that secondary stop up a bit to get it to idle.
Best way is to flip the carb. I got tired of guessing and got a dual wideband takes the guess work out of carb tuning.
 Is your exhaust crossover open?  Choke setup?

ZLP955

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Re: 69/302 idle problem
« Reply #11 on: April 25, 2020, 07:17:41 AM »
When it dies, can it be restarted straight away, or does it need some time before it'll fire up again?
If it has fuel in the bowls after stopping, fuel delivery seems unlikely (at least to the carb). Maybe the ignition needs a closer look - could be a bad coil, once it warms up; vacuum advance; charging system. So many things to investigate, one at a time. How do the plugs look?
Tim in Australia.
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NED

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Re: 69/302 idle problem
« Reply #12 on: April 25, 2020, 01:17:08 PM »
Check distributor dwell also. Points may have slipped.
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ssl78

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Re: 69/302 idle problem
« Reply #13 on: April 25, 2020, 04:05:27 PM »
Make sure you do not have a bad brake booster or pcv valve by crimping the lines

bobs69z

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Re: 69/302 idle problem
« Reply #14 on: April 25, 2020, 05:42:55 PM »
Car restarts after it dies. Dwell is set at 30. Points were just replaced. Tight lash Comp cam. Valves set at 16. How do you check pcv or brake booster by crimping line?
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