Feedback Carb
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Elder User
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From: Raleigh, NC
Feedback Carb
I picked up a carb off an '84 F150 351W and want to know if it can be used without a computer. Anyone know where I can find a description of the computer controlled functions and maybe how the carb can be modified to work without a computer?
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From: Virginia
If it has lots of wires coming out of it, it's computer controlled. Unless you can find someone who has experimented and found a way to re-calibrate the carb to not need the computer control, you can't really use it. It will function without the wires hooked up, but it won't be right.
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there actually
Duraspark and metering block - The Ranger Station Forums
There is a diagram and set of pictures on the net somewhere..I'm sure you'll find it if you search...
Actuallty I think it was this guy..
http://www.therangerstation.com/forums/member.php?u=41
that made the blocks..if you search his posts you'll see it.
if you don't do this the mixture will most likely be too rich..but it WILL run.
Cargo Master
Joined: Aug 2007
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From: New Zealand
You can use a feedback carb without the computer input.
I had one on my 351W & ran it for a while without a computer, before swapping for a non-feedback carb.
I swapped because the feedback carb was from a 302 that had been in the truck earlier, with a smaller venturi (I removed the emissions & ECM).
The feedback carbs (2150 at least) seem to only fine-tune via the ECM & don't give a lot of mix variation; so as long as the carb is jetted ok for your engine, there isn't much issue with not having it connected.
Disconnected, the carb goes to the rich end of it's mix range, which in my experience wasn't rich enough to carbon up the plugs or significantly affect mileage.
Having said all that, there is this conversion I found on line which lets you adjust mixtures manually if you want to -
http://www.cardomain.com/ride/500837/3
But I would try your carb as is first.
PS - John's beaten me to it
I had one on my 351W & ran it for a while without a computer, before swapping for a non-feedback carb.
I swapped because the feedback carb was from a 302 that had been in the truck earlier, with a smaller venturi (I removed the emissions & ECM).
The feedback carbs (2150 at least) seem to only fine-tune via the ECM & don't give a lot of mix variation; so as long as the carb is jetted ok for your engine, there isn't much issue with not having it connected.
Disconnected, the carb goes to the rich end of it's mix range, which in my experience wasn't rich enough to carbon up the plugs or significantly affect mileage.
Having said all that, there is this conversion I found on line which lets you adjust mixtures manually if you want to -
http://www.cardomain.com/ride/500837/3
But I would try your carb as is first.
PS - John's beaten me to it
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From: Raleigh, NC
Now I'm wondering if an earlier, not computer controlled, carb was put on the '84 F150 I got the carb from. Carb is a Motorcraft made by Holley, list 8343. Looks like this one R8343 Carburetor Info Page which is for '79-'83 trucks.
Carb has a single metering block but I don't find any idle mixture screws.
And, the only wire attachment point I found was for the electric choke. The carb and intake were removed from the engine when I found it.
BTW, there was a vacuum line running directly from the vacuum tree to the air horn. Seems like that would be a big vacuum leak.
Carb has a single metering block but I don't find any idle mixture screws.
And, the only wire attachment point I found was for the electric choke. The carb and intake were removed from the engine when I found it.BTW, there was a vacuum line running directly from the vacuum tree to the air horn. Seems like that would be a big vacuum leak.
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From: Virginia
None of the holley 4 barrels I know of were computer controlled. That carb in the picture is definitely not computer controlled. Did you get a great deal on that carb? If that's the type carb you want to use, I personally would just buy a brand new one from jegs or summit racing. I believe you can get them for $250-$300. And they won't have all those hose connections that you will have to plug off.
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Elder User
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From: Raleigh, NC
None of the holley 4 barrels I know of were computer controlled. That carb in the picture is definitely not computer controlled. Did you get a great deal on that carb? If that's the type carb you want to use, I personally would just buy a brand new one from jegs or summit racing. I believe you can get them for $250-$300. And they won't have all those hose connections that you will have to plug off.
So, now I can try this carb out when the time comes.Yes, I got the carb cheap along with some other parts. I have a 600 CFM Holley on the 351 now but its not running just right. May be tune or may be something's not right with it. Thought I'd slip this carb on and see if it does any better.
Thanks for the help.
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From: Raleigh, NC
No thanks. When I thought this was a feedback carb I was trying to find out if it could be made to work without a computer. Not an issue now.
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From: Virginia
I hate to be negative, but the chances of a carb that has been sitting around actually working by just bolting it on are slim to none. The lousy gas they sell now turns to crud inside the carb, and all the gaskets and seals sit around and dry out and get hard, and then they like to leak when you try to use it.
The reason the mixture screws are blocked off is because that is a emissions carb. That is also a sign that carb has never been rebuilt. If after you try it you find it needs a kit, and you have another holley that does not have all that emissions stuff on it, I think I would invest the time and kit into the non-emissions carb. If you end up rebuilding one or the other, write back in there is a trick you need to do to help make it right.
The reason the mixture screws are blocked off is because that is a emissions carb. That is also a sign that carb has never been rebuilt. If after you try it you find it needs a kit, and you have another holley that does not have all that emissions stuff on it, I think I would invest the time and kit into the non-emissions carb. If you end up rebuilding one or the other, write back in there is a trick you need to do to help make it right.
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From: Raleigh, NC
I previously rebuilt the 600 Holley and had it on a 347 SBF in a Maverick. 
That engine wouldn't run well until I replaced the Holley with a QuikFuel and the HEI distributor with MSD 6AL and MSD dist. Never knew if the problem(s) was/were the carb, ignition or both.
For the '81 F150, I rebuilt 5.8L out of a '95 F150, changing it to carb and MSD ignition. Tried the rebuilt Holley, just in case the previous problems were all ignition, and the engine has some hesitation. Haven't tried different jets, etc., yet. I have a jet kit so it won't cost me anything to try some things.
When I came across this cheap carb from an '84 351 I figured I'd put it on and see if it made any difference. There wasn't any tag on the carb so I'm thinking it has been rebuilt but maybe by a non-expert like me. The vacuum line directly from the tree to the air horn makes me think whoever worked on it might be dumber than me about this stuff. If the engine doesn't run any better with the Motorcraft carb I'll see if I can get the rebuilt Holley working better.
What's the trick you mentioned?
That engine wouldn't run well until I replaced the Holley with a QuikFuel and the HEI distributor with MSD 6AL and MSD dist. Never knew if the problem(s) was/were the carb, ignition or both.For the '81 F150, I rebuilt 5.8L out of a '95 F150, changing it to carb and MSD ignition. Tried the rebuilt Holley, just in case the previous problems were all ignition, and the engine has some hesitation. Haven't tried different jets, etc., yet. I have a jet kit so it won't cost me anything to try some things.
When I came across this cheap carb from an '84 351 I figured I'd put it on and see if it made any difference. There wasn't any tag on the carb so I'm thinking it has been rebuilt but maybe by a non-expert like me. The vacuum line directly from the tree to the air horn makes me think whoever worked on it might be dumber than me about this stuff. If the engine doesn't run any better with the Motorcraft carb I'll see if I can get the rebuilt Holley working better.
What's the trick you mentioned?
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From: Virginia
Here's a link to a picture. I used to have access to a milling machine, and I have fixed several "problem" Holley carbs.
Holley Restore Clamped In Milling Device Photo 8
The 4 screws that hold the metering plate and the fuel bowl onto the main body like to pull the main body high on the 4 corners where the body is threaded for these screws. All those little holes in the middle will be low, and the gasket will not seal correctly. It usually will work for a short time till the gasket shrinks after a few days to a week after a rebuild.
While a milling machine is the best, a large flat file can be used but you need to be very careful with it. Hold it as flat as possible and only go a few strokes before changing directions. Don't file it all from one direction.
If you have a good file laying around, you can run a couple of strokes across it and you will see how bad it is. I bet it's pretty bad. I only worry about the front of the body, the ones I have been doing are the cheaper carbs with no rear metering block, so there is not a problem on the secondary side on those type carbs.
Holley Restore Clamped In Milling Device Photo 8
The 4 screws that hold the metering plate and the fuel bowl onto the main body like to pull the main body high on the 4 corners where the body is threaded for these screws. All those little holes in the middle will be low, and the gasket will not seal correctly. It usually will work for a short time till the gasket shrinks after a few days to a week after a rebuild.
While a milling machine is the best, a large flat file can be used but you need to be very careful with it. Hold it as flat as possible and only go a few strokes before changing directions. Don't file it all from one direction.
If you have a good file laying around, you can run a couple of strokes across it and you will see how bad it is. I bet it's pretty bad. I only worry about the front of the body, the ones I have been doing are the cheaper carbs with no rear metering block, so there is not a problem on the secondary side on those type carbs.