1985 Ford Mustang Engine won't idle unless the the adjustme

Tiny
TMASTRACCHIO
  • MEMBER
  • 1985 FORD MUSTANG
  • V8
  • 2WD
  • MANUAL
  • 135,000 MILES
Just a little history. The car has always been a great runner, 24mpg on the highway. The motor has about 45,000 miles since it was freshened up. I was driving at about 45 mph and lifted off the throttle quickly, after that it stalled and wouldn't idle. I had to turn the throttle adjustment screw all the way in so I could drive home without stalling. It drove fine and didn't seem to have lost any power but I know there is something that isn't right. I have replaced all the vacuum hoses I could see and checked the vacuum guage after each hose replacement. Not much improvement, so I plugged all the hoses and fittings from the intake and carb. The guage reads 15" @1000 rpm with all the vacuum lines plugged. Is that a normal reading for a 5.0 liter? I haven't removed the carb yet, maybe a piece of gasket broke off and that is where the leak is, I'll check that tomorrow. I can't really hear any vacuum leaks, last time I checked the timing I set it to 10 degrees BTDC. Let me know what you think about this, I'm a little stumped.

Thanks,
Tom
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Monday, February 23rd, 2009 AT 12:44 AM

7 Replies

Tiny
RACEFAN966
  • EXPERT
Ok what carb is on it? I know it will be a motorcraft but there are a couple of different ones. If you like take a pic of it and include it in your response. Also have you checked the plugs cap and rotor and have you used a spray bottle to check the intake for vacuum leaks? Get back to me and we will go from there.
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Monday, February 23rd, 2009 AT 2:48 PM
Tiny
TMASTRACCHIO
  • MEMBER
I checked the cap and rotor, no cracks. I sprayed the base of the intake with windex and didn't hear a change in the idle. I checked the plug wires with a neon spark tester and all eight plugs are firing. I attached some photos of the carb.


http://www.2carpros.com/forum/automotive_pictures/322003_IMG_2371_1_3_1_2.jpg



http://www.2carpros.com/forum/automotive_pictures/322003_IMG_2371_1_3_1_2.jpg



http://www.2carpros.com/forum/automotive_pictures/322003_IMG_2372_2_3_1_2.jpg

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Tuesday, February 24th, 2009 AT 9:38 AM
Tiny
RACEFAN966
  • EXPERT
Ok so you have a holley 4bb carb. No problem. So first check for any vacuum leaks around the base of the carb. Check the brake booster for any vacuum leaks too.
Now there is on black smoke coming out of the tail pipe is there? Have you slightly snuffed the carb with you hand to make it rich and see if it helps or spray short bursts of carb cleaner in it while it running to see if that helps it want to idle better? Get back to me with all the info you can so we can figure this out
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Tuesday, February 24th, 2009 AT 10:37 AM
Tiny
TMASTRACCHIO
  • MEMBER
Currently I have all the vacuum lines from the manifold and carb blocked off. If I read 15" of vacuum is that too low?

Thanks,
Tom
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Tuesday, February 24th, 2009 AT 10:33 PM
Tiny
RACEFAN966
  • EXPERT
No that is good the higher the elevation you are at he lower the reading will be too. So did you slightly snuff the carb with your hand and see if that helped?
Also you can probably hook all the vacuum lines back up. If you need to adjust it then they will all need to be hooked up to adjust it right. Get back to me as to weather snuffing the carb or short bursts of carb cleaner sprayed in carb helpes it idle or idle higher.
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Wednesday, February 25th, 2009 AT 10:12 AM
Tiny
TMASTRACCHIO
  • MEMBER
I'm glad to hear that 15" of vacuum is ok. I haven't snuffed the carb yet, but I removed the carb and saw that there was no gasket between the carb and the heat shield. I'm surprised it never gave me any trouble before, this is the first time I have ever removed the carb since I bought the car. I have to pick up new gaskets tomorrow and when I get it put back together I'll let you know.
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Thursday, February 26th, 2009 AT 1:37 AM
Tiny
RACEFAN966
  • EXPERT
Ok thats great this gasket missing could be causing some of the problems. Get back to me with how it goes.
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Thursday, February 26th, 2009 AT 10:39 AM

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