Idling Issues
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Tuned
Joined: Sep 2013
Posts: 453
Likes: 19
From: Little Rock, AR
Idling Issues
Did some searching and haven't seen the answer to this, but I may have missed it too.
1983 F100 300 I6. Carter YFA with manual choke.
Freshly rebuilt carb, new spacer and carb gasket bolted down good n tight. No vacuum leaks to be found.
Pretty odd, there's no fast idle linkage, so I have to pull the manual choke out, crank, hit the pedal right as it fires up and immediately push the choke in to open it. Then I have to hold pedal at about 1000 RPM. I know that issue would be solved with the fast idle cam set properly.
The REAL issue is the idle settings. I have to screw the idle speed way in to keep it running at 800 RPM. If I screw the idle mix all the way in, it keeps running, so I'm suspecting I'm hitting the transfer slot.
What do I need to do to be able to back the idle speed off and use the idle circuit as it is intended? As stated, carb was cleaned and rebuilt. Btw, it has done this since I originally owned it 4 years ago. I'm just getting around to fixing it now.
1983 F100 300 I6. Carter YFA with manual choke.
Freshly rebuilt carb, new spacer and carb gasket bolted down good n tight. No vacuum leaks to be found.
Pretty odd, there's no fast idle linkage, so I have to pull the manual choke out, crank, hit the pedal right as it fires up and immediately push the choke in to open it. Then I have to hold pedal at about 1000 RPM. I know that issue would be solved with the fast idle cam set properly.
The REAL issue is the idle settings. I have to screw the idle speed way in to keep it running at 800 RPM. If I screw the idle mix all the way in, it keeps running, so I'm suspecting I'm hitting the transfer slot.
What do I need to do to be able to back the idle speed off and use the idle circuit as it is intended? As stated, carb was cleaned and rebuilt. Btw, it has done this since I originally owned it 4 years ago. I'm just getting around to fixing it now.
FTE Legend
Joined: Nov 2015
Posts: 30,828
Likes: 4,094
From: Angier, NC
The rebuild paper should tell you how many turns out from lightly seated mixture screw it should be set to as a starting point.
If not I would try 2 turns out as a start and go in or out as needed.
Dave - - - -
If not I would try 2 turns out as a start and go in or out as needed.
Dave - - - -
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Tuned
Joined: Sep 2013
Posts: 453
Likes: 19
From: Little Rock, AR
The carb is open too far, yes but only because that's the only way to keep it running. It will NOT idle with only the 2 turns (or anything close).
FTE Legend
Joined: Nov 2015
Posts: 30,828
Likes: 4,094
From: Angier, NC
So the idle is too high so the idle mixture screw does nothing?
You backed the mixture screw out 2 turns what if you try 3 turns out? Maybe 4 turns out?
If that does not work then you either have a vacuum leak somewhere or the carb has a passage plugged.
If you have air pull the mixture screw out first spray carb cleaner in there followed with air.
Put screen it and back out 2 turns to start and go from there.
Dave - - - -
You backed the mixture screw out 2 turns what if you try 3 turns out? Maybe 4 turns out?
If that does not work then you either have a vacuum leak somewhere or the carb has a passage plugged.
If you have air pull the mixture screw out first spray carb cleaner in there followed with air.
Put screen it and back out 2 turns to start and go from there.
Dave - - - -
Moderator
Joined: Jan 2001
Posts: 56,949
Likes: 2,718
From: Virginia
I wonder what shape your EGR valve is in? Does it have a piece of carbon in it holding it open all the time? You are getting unwanted air from somewhere, so you are having to idle the engine way up to keep it running. Also look for bad gaskets and cracks in and around the intake manifold where it bolts up to the head.
Take the line off the brake booster in case the booster has a bad leak inside it. Make sure your PCV valve is working ok and hooked up correctly.
Take the line off the brake booster in case the booster has a bad leak inside it. Make sure your PCV valve is working ok and hooked up correctly.
Tuned
Joined: Dec 2017
Posts: 308
Likes: 8
Check your vacuum line routing. I have a 1983 yfa just like yours.
For a while I had my idle speed cranked way up just to keep the truck running. My mixture screw did basically nothing to the speed or quality of the engine's cycle.
I was looking for a vacuum leak to explain the extra air getting in, and I discovered two lines were flip flopped on the passenger side of the carburetor, which led between the vacuum tree, the carb, and the distributor. After I got them in order based on the diagram on the radiator support, the engine ran much better.
I was able to back off the idle speed until it ran very smoothly at 600 where it is now. Hopefully this will fix your problem.
For a while I had my idle speed cranked way up just to keep the truck running. My mixture screw did basically nothing to the speed or quality of the engine's cycle.
I was looking for a vacuum leak to explain the extra air getting in, and I discovered two lines were flip flopped on the passenger side of the carburetor, which led between the vacuum tree, the carb, and the distributor. After I got them in order based on the diagram on the radiator support, the engine ran much better.
I was able to back off the idle speed until it ran very smoothly at 600 where it is now. Hopefully this will fix your problem.
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