Car Will Not Hold Idle

Tiny
DAVEGOFF
  • MEMBER
  • 1978 FORD MUSTANG
  • 5.0L
  • V8
  • RWD
  • MANUAL
  • 99,225 MILES
Drove the car six days ago with no problems. This morning, it was slow to start and when it did, it would not maintain idle. The engine would die. All vacuum lines appear to be connected. I held the rpm at 2000 long enough for the engine to come up to temperature, and it would still die rather than idle. I drove the car around the yard in first-second gears and it would spin the back tires. But it would die as soon as I came off the gas. New battery, full tank of new gas, rebuilt carburetor.
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Thursday, August 18th, 2016 AT 6:44 PM

6 Replies

Tiny
CJ MEDEVAC
  • EXPERT
It was fine after the carburetor was built?

Insure the carburetor is snugged down to the intake.

Snug (not over-tighten) the screws on the carburetor, but no the mix screws! Leave them alone.

Continue to look for broken/ cracked/ loose/ off - vacuum lines.

Breather is clean?

Fuel filter is good?

Any issues from before six days ago, like driving through high water/ etc?

The Medic
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Thursday, August 18th, 2016 AT 7:41 PM
Tiny
DAVEGOFF
  • MEMBER
Car drove just fine, no issues. Did just convert air conditioner compressor to a Sanden unit, but drove home from shop just fine. Carburetor was rebuilt five months back and has worked okay until this morning. Have been told that vacuum leaks would probably cause faster idle but probably not dying at idle. New air filter and new fuel filter. Distributor bolted firm and distributor cap new. Problem occurs whether air conditioner is on or off. Stumped.
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Thursday, August 18th, 2016 AT 7:48 PM
Tiny
CJ MEDEVAC
  • EXPERT
Try this.

Mix screws.

screw them in till they lightly touch bottom ("lightly touch not cram")

For each one count the number of turns (or 1/2 turns) on the way down

Now you know how far to turn them to get back to the starting point

WRITE THIS DOWN! YOU MAY NEED THIS INFO LATER!

Back them back out however many turns you came up with, you should be at the place you started

Normally, both will have the same number of turns.

Running the same?

Let's try a half turn "in" on both screws

No change?

Go back 1/2 turn out on both (our original starting point)

What about 1/2 turn out on both from this point?

Any improvements, lets go 1/4 turns (in or out) to make it better on both screws

MESS UP? Screw 'em to the bottom again and look at your paper to get them back to the original starting point!

A meter would help greatly!

See my answer in this link, it might help you along! (2 pages long)

https://www.2carpros.com/questions/jeep-cj7-1985-jeep-cj7-stalls-when-hot

Return here with good news!

The Medic

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Thursday, August 18th, 2016 AT 8:07 PM
Tiny
CJ MEDEVAC
  • EXPERT
I get carried away!

1st

Let's make sure the choke is not on

or

Your breather is not interfering with the choke's linkages.

Carry on soldier!

The Medic
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Thursday, August 18th, 2016 AT 8:27 PM
Tiny
DAVEGOFF
  • MEMBER
You were right on by suggesting the carb may not be bolted down tight enough. Tightened her down and that corrected the idle problem. Now the car has returned to its earlier problem of losing power when the engine is put under load. Have rebuilt/replaced the following: carb, distributor, coil, solonoid, ignition module, fuel filter at carb, fuel filter in tank, all rubber fuel lines, gas cap, air filter, etc. Don't know if we have a fuel starvation problem or an electrical problem. Any help appreciated. Thanks!
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Sunday, August 28th, 2016 AT 7:42 PM
Tiny
CJ MEDEVAC
  • EXPERT
Can you detect a skip in it while it runs? (Answer this)

Keep looking for vacuum leaks

In the mean time, this is a simple test.

Hook up Mr. Timing light.

Unhook and plug the vacuum advance hose with a bolt/ pencil/ whatever.

Insure you are at the correct idle speed to time it.

Check your timing - adjust if necessary.

Now Then

Keep the light on the marks

Slowly throttle up the carb (slow, to maybe 2000 RPM, just guess at it)

Is the timing mark moving further and further from correct timing?

'Nuther words, you should see the mark moving to compensate for increased engine speed (thus your spark gets thrown sooner and sooner)

If it ain't moving (it is still on your original timing) The Mechanical advance inside the distributor may be hung up OR most commonly the/ a spring that pulls the centrifugal weights back to return to center (when at lower RPMs) may have broken.

This is the results of this happening

1) The weights go outward all of the time

2) This immediately makes the timing back up (constantly, it is now way off)

3) Dumbfoundedly, you FINALLY check the timing

4) It is off a good bit

5) You change it to correct timing (the weights are still centrifugal-ed out- You don't realize it)

6) Timing is right!

7) There is no longer a mechanical advance, the faster you run the engine, the spark is not firing sooner as it should.

8) Lack of power/ just don't wanna pick up speed/ even backfiring may occur

Replace the distributor

Re-time it, as it was actually wrong with the spring being broken (and you moved it to compensate)

How'm I doin'?

The Medic
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Monday, August 29th, 2016 AT 3:32 PM

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