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1986 Ford F-150 complicated carb adjustment

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1986 Ford F-150 complicated carb adjustment

Old 10-30-2018, 07:06 PM
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Default 1986 Ford F-150 complicated carb adjustment

Hey all. Ok so I need help as soon as possible. Apparently I have one of the "weird" carbureted trucks. I have a 1986 F-150 with a 300 inline 6, and I'm having the worst time getting it to run right. It's running way too rich, you can smell it, I have already done plugs and wires and yes it sucks air just fine. The issue with this carburetor is that it can't be adjusted by the two screws on the normal 1 barrel carbs on the older models.... it states something about an EEC IV on the sticker up front and also states the carburetor can't be adjusted.... so how in the world do I fix this? I've never seen a carburetor you can't adjust. I've tried the screws but they are absolutely attached to nothing on the other side so why put them there anyways? Anyway if you all can help me please do I need to know how to get it to run right.
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Old 10-31-2018, 12:20 AM
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The accelerator pump diaphragm is probably ruptured - that's what happened to mine that caused me to switch it to EFI (the only way to make it run right). The sticker says it can't be adjusted, but they just made it REALLY-difficult to adjust by putting a spinning cap over the idle mixture screw head. Look at the bottom of this diagram & its caption:


(phone app link)


It's difficult to rip the cap off to get at the screw, but it can be done. The Haynes manual explains how:


(phone app link)
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Old 10-31-2018, 03:44 PM
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Originally Posted by Steve83 View Post
The accelerator pump diaphragm is probably ruptured - that's what happened to mine that caused me to switch it to EFI (the only way to make it run right). The sticker says it can't be adjusted, but they just made it REALLY-difficult to adjust by putting a spinning cap over the idle mixture screw head. Look at the bottom of this diagram & its caption:


(phone app link)


It's difficult to rip the cap off to get at the screw, but it can be done. The Haynes manual explains how:


(phone app link)
thank you buddy I'll look into it
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Old 11-09-2018, 12:25 AM
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What is the vacuum reading when put on the vacuum block above the exhaust manifold??????
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Old 11-10-2018, 11:25 PM
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When you say you can't get it to run right, it runs rich, and all that stuff, are you talking about only at idle? Because all adjusting that screw is going to change is idle. If the truck runs like garbage once you are using the accelerator pedal, then you have a bigger issue than the cap on the screw.
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Old 11-11-2018, 11:54 AM
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Originally Posted by burnthelight88 View Post
When you say you can't get it to run right, it runs rich, and all that stuff, are you talking about only at idle? Because all adjusting that screw is going to change is idle. If the truck runs like garbage once you are using the accelerator pedal, then you have a bigger issue than the cap on the screw.
it runs rich period. Like at idle its lopey like its cammed out but when driving it seems fine but I can see a little bit of smoke coming out when I stomp it. I do wonder is it possible I can put an older model carburetor on it? One that is adjustable or is that not an option?
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Old 11-12-2018, 08:13 AM
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Originally Posted by Austin Harden View Post
it runs rich period. Like at idle its lopey like its cammed out but when driving it seems fine but I can see a little bit of smoke coming out when I stomp it. I do wonder is it possible I can put an older model carburetor on it? One that is adjustable or is that not an option?
depending on where you live, it might not have to go through emissions. If so, you can put any carb on it you want. I suggest this combo.

https://www.summitracing.com/parts/ofy-6019dp

https://www.summitracing.com/parts/h...3570/overview/
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Old 11-12-2018, 12:34 PM
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You're missing the point here. Adjustment screws only affect idle.

Running rich period would point to an overall carb problem, not an idle adjustment screw problem. Jets, float, needle valves all come to mind. "Smoke from your tailpipe" could be nearly anything. In his first post, Steve suggested the accelerator pump diaphragm possibly being blown out. I tend to agree, and that could be one of several carb issues you're having. When was the last time it was rebuilt? You can replace the accel pump diaphragm very easily, but its not terribly difficult to rebuild the whole thing. Post a picture of the carb so we can see what it is.

You can always switch to a different carb, but unless you're buying new they could also need a rebuild. You need to rebuild. The Offy intake suggested by Tempest is really nice if you're going the brand new parts route.
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Old 11-18-2018, 07:29 AM
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Originally Posted by burnthelight88 View Post
You're missing the point here. Adjustment screws only affect idle.

Running rich period would point to an overall carb problem, not an idle adjustment screw problem. Jets, float, needle valves all come to mind. "Smoke from your tailpipe" could be nearly anything. In his first post, Steve suggested the accelerator pump diaphragm possibly being blown out. I tend to agree, and that could be one of several carb issues you're having. When was the last time it was rebuilt? You can replace the accel pump diaphragm very easily, but its not terribly difficult to rebuild the whole thing. Post a picture of the carb so we can see what it is.

You can always switch to a different carb, but unless you're buying new they could also need a rebuild. You need to rebuild. The Offy intake suggested by Tempest is really nice if you're going the brand new parts route.
Rebuild on this carb would be a snap. www.rockauto.com has the rebuild kit fro 13$!! The also sell new carbs for that truck in the 250$ range with a core charge. New always takes out the guess work if you are not savvy to rebuild. But since the truck is so old, I would upgrade to a bigger carb if you plan to replace..
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Old 11-18-2018, 08:49 AM
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Rebuilding a carb can seem scary but is actually pretty easy. Do a rebuild and then see what you have.
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