1968 Mustang Stalls at lights - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 07-03-2019, 08:45 PM Thread Starter
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1968 Mustang Stalls at lights

Guys,

I need help! My 1968 289C auto stalls at lights when I come to a stop. Runs great all around but when I come to a stop at a light it just about dies or does dies. I fire it back up and take off with no problems. I have no power brakes or boosters and I'm running a Edlebrock carburetor on her. Any suggestions or ideas? I was told it should tune the carburetor and put it in drive with help and adjust the idle screw to increase my rpm in drive. I'm completely novice when it comes to carburetors and fixing issues like this, really clueless. I started messing with the carburetor screws and I think I messed it up even worse now. It's preventing me from driving Barbara right now. I literally just put new wheels on a few days ago and I'm ready to show her off.


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post #2 of 15 (permalink) Old 07-03-2019, 08:46 PM
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Nice looking car..



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post #3 of 15 (permalink) Old 07-03-2019, 09:01 PM
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Quote:
Originally Posted by jakeinarkansas View Post
Any suggestions or ideas?
What RPM does the engine idle at with the trans in P or N? What does the idle RPM drop to when you put the trans in D with your foot on the brake?
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post #4 of 15 (permalink) Old 07-03-2019, 09:13 PM Thread Starter
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P was my 950 and drops down to 400-500 when I put it into R or D with my foot on the brake. I'm out here now trying to figure out what to do.
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post #5 of 15 (permalink) Old 07-03-2019, 10:22 PM
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A 500 rpm drop from P to R or D sounds excessive to me. The bandaid fix is to set the idle speed higher.
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post #6 of 15 (permalink) Old 08-17-2019, 11:17 AM Thread Starter
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Thanks. I got that correct, for now. I think i need to replace the carburetor, replace spark plugs and dis cap, fuel filter, and may so gas tank cleaner or something.
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post #7 of 15 (permalink) Old 08-17-2019, 12:14 PM
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950 is way too high at idle in park. When you set it to 600, where does it drop too in gear ? Sure sounds like a bad torque converter. Also, check your ignition timing.

Cliff
1966 Blue Hardtop. 200 CID with 3 Speed Trans
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post #8 of 15 (permalink) Old 08-17-2019, 12:23 PM
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If you have to set it at 950 to get it to idle, you could have a vacuum leak...that would cause the stall as well when it drops to 500.

Easy to check vacuum with a gauge before you replace everything.

Allen

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My go fast build thread: Go Fast Build Thread
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post #9 of 15 (permalink) Old 08-17-2019, 12:36 PM
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The Edelbrock carb is not very complex. Watch these two videos put out by Hagerty to see what's inside your carburetor. Perhaps this will encourage you to do a little more research on your own, get a rebuild kit, and fix the carburetor you have yourself. I bet you can do it successfully.


If you decide to take this on, definitely watch more videos. Don't just use these 2 videos.





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post #10 of 15 (permalink) Old 08-17-2019, 01:53 PM
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Ok, I can't add any additions things to check. But I can offer, first insure the easy basic tune-up points are checked or verified.
Don't be intimidated by these issues. Folks here have a lot of knowledge and a strong willingness to help. Also, it's never advisable to "play" with the carb settings or any settings, for that matter, without knowing what you're doing. As you stated, you don't know about them.

First things First.....
1. Adjust Point gap to specs. if you don't know, check your manual. If you don't have a manual, get one.
2. Clean and gapped all plugs to specs
3. Check all plug cables for correct firing order are clean and in good shape (no cracks)
4. Check and adjust timing per specs.

The Carb:
1. "Gently" re-seat both Air Mix screws (front of carb), then, turn out approx. 1.5 to 2 turns ( I believe, this is the basic setting)
2. Insure all of the linkage is clean and free to operate.
3. Adjust the idle speed to specs., using the idle adjustment screw on the side of the carb, where the throttle linkage is attached.
4. Verify the choke is fully open as noted by a vertical choke plate when the engine is warm. When cold, the choke plate should be closed, but, for an approx. 1/8" gap between the plate and the air horn (metal section surrounding it)

Vacuum
1. Vacuum leaks create all sorts of havoc with any engine.
A good tool for checking for leaks and learning the over-all health of your engine is a VAC gauge. It connects to the "full" vac port on the front of the carb. A healthy engine's Vac reading will be in the high teens, if not low 20s Hgs. Basically, the higher the VAC the healthier the engine. A wildly fluctuation needle is an indication of problems.

1. Insure the vacuum line to the modulator on the side of the transmission is in good condition. That is, the short rubber section at the modulator is firmly seating and in good condition. FYI, this is often over-looked and can be a source of vacuum leaks.
2. Based on what you stated, your other vac line to check is the one from the distributor vac canister to the base of the carb. Verify it's in good condition.

I did't really mention anything new that wasn't already offered by the guys here offering help. I just re-stated it in a way to make it easier for a Novice to understand. Good Luck and keep us posted on your results.

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Last edited by kenash; 08-17-2019 at 01:56 PM.
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post #11 of 15 (permalink) Old 08-17-2019, 02:08 PM
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I'll add to the above that the vacuum canister on the distributor also needs to be checked to see that it holds a vacuum. My old vacuum canister had a torn diaphragm inside so even though the vacuum line to it was good, the canister itself caused a vacuum leak in addition to not functioning.
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post #12 of 15 (permalink) Old 08-17-2019, 02:32 PM
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Did this issue all of a sudden start happening out of the blue when no one had touched the engine recently? Or has it always been this way with the edelbrock you have?

Dave
'68 GTCS
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post #13 of 15 (permalink) Old 08-17-2019, 02:59 PM
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Quote:
Originally Posted by awhtx View Post
A 500 rpm drop from P to R or D sounds excessive to me. The bandaid fix is to set the idle speed higher.
It is excessive. But, if the idle circuit is not clean, this could happen as the engine would be starving. I just went through some issues with my Edlebrock 1403. Here is a link to the thread.
https://forums.vintage-mustang.com/v...e-mixture.html
There is a lot of stuff in here about ported vs. manifold vacuum and initial timing. I notice that you have your vacuum connected to the ported vacuum nipple. The manifold vacuum nipple is on the driver side of the front of the carb. I also notice that you have an original dual diaphragm distributor. Not sure what you have the "rear diaphragm" vacuum hose on the vacuum canister connected to. I think most people get rid of the dual diaphragm distributors (an early and awkward attempt to reduce emissions ) and get a single diaphragm one unless they are going concours or need it a state that does emission test antique cars.


The bottom line is that the tiniest blockage in the idle circuit could be your issue. Also, note the slight difference in the venturi gasket I got in the rebuild kit versus the original venturi gasket.


Hopefully, some of the really smart guys who helped me will see this thread and offer their thoughts.

Dave
'68 GTCS
8R01J
C4/PS/PB/AC
2/8/1968
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post #14 of 15 (permalink) Old 08-17-2019, 09:46 PM
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It looks like you still have your vacuum hoses running to the DVCV on the thermostat housing and the dual-vacuum distributor. That's fine and shouldn't be the cause of your problem. I agree that your idle speed is too high. Curb idle, in drive, should be around 600 rpm for an engine with a stock cam or one with a wide LSA like an "RV" grind and when shifting back to Park or Neutral from drive I wouldn't expect to see more than a 150 rpm rise. I would suggest going back to a base-line with the carb, as if you were installing it fresh, as far as primary and secondary idle settings and idle mixtures are concerned as well as looking at ignition timing. If you don't find an issue there, I'd look at a vacuum leak or a carburetor idle circuit issue that won't allow you to close the throttle plates.

Also of note is the lack of a throttle dashpot... the small bell-shaped unit that installs near the throttle linkage and dampens the action of the throttle closing on automatic transmission-equipped cars to prevent stalling when you lift the gas pedal. They DO make them for Edelbrock installations.

As asked previously, has it run this way ever since the carb was installed?
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post #15 of 15 (permalink) Old 08-18-2019, 12:45 AM
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Could be vapor lock. Depends on the gas I use but I get it pretty bad to where my car dies after a short drive and then restart. I have an air fuel gauge and can see how lean it goes after sitting then starting again. Try non-ethanol and might help if this is the problem. I even get a bit of vapor lock on longer in town drives without even stopping.
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