I was driving my truck when I smelled a strong gas odor coming from under the hood, pulled over popped the hood and I had gas pouring out of the vent tube off the carb. Recently I have changed the fuel filter and reset ignition timing. I don't hardly know much about carburetors and don't know why this would happen. The truck won't idle and I get lots of black smoke coming from the tailpipe. It's definitely flooding out horribly and takes a lot of cranking and effort to get it to restart.

 

Possibly you float needle/seat is sticking. Maybe when you changed the filter some dirt got in the line and is holding the needle off its seat (allowing carb to flood). Do you have an electric fuel pump on this truck?

 

Keep a fire extinguisher with you; this is a guy in Canada who had just that day finished restoring his truck:

Windsor truck fire - YouTube

Downtown Windsor Truck Fire - YouTube

Aftermath of Windsor Truck Fire - YouTube

 

I'm not sure if I have an electric fuel pump or not, I have never checked. Is the float hard to get to on these little carbs?

I did... After I stopped I had my wife bring me our kitchen extinguisher before I attempted to get it home....

 

So I took the carb. apart, the float wasn't full of gas and the inside of it looked like you could eat off it, no carbon build up, no white build up, no dirt, as far as my untrained eye could see everything looked great. Put it all back together, started it up, no gas out of the vent anymore, it was easy to start, but there was small small leakage coming from a screw on the bottom of the carb.... So I pulled it again, tightened up the four screws I saw facing upwards towards the air intake, re-installed all of it, started it up, it ran BEAUTIFULLY. No leaks, no gas smell, no gas coming out of the vent orifice. All seems well.... for now, but I still can't imagine what was causing it, unless after sitting a while (I don't drive it much, maybe once or twice every 2 weeks) the needle got stuck and pulling the carb and moving the float up and down freed it up.

 

I would say the other poster is probably correct, when you changed the fuel filter a little something got in and held the needle valve open that the float actuates. Hopefully it will never happen again, all the foreign material hopefully made it's way through. If it keeps happening, I would suspect a faulty new fuel filter.

I don't know if you guys realize this, but you really can't trust anything you buy in the store anymore. There is absolutely no quality control at all, and some things just fail right out of the box. It's happened to me so many times, I now am somewhat reluctant to do regular maintenance and tune-ups. I of course change the oil on a regular basis, but if the engine is running good, I am now starting to leave the ignition system and the other parts alone till they start giving me trouble. I am tired of taking good used sparkplugs and wires off, and replacing them with new faulty ones. And I have had faulty fuel filters before that let dirt through to the carb. You never know, the piece of dirt may have come from the filter itself, from the manufacturing process. It would not surprise me.

 

I couldn't agree more. I've bought so many new parts that have failed right out of the box. I once bought an alternator (reman) form autozone for my old '79 F150 that failed right out of the box, i took it back to them without them knowing I bought it from them, had them test it, and it of course failed. I really hope this doesn't happen again, but in case it does, I have an extinguisher handy, as well as the tools to get the carb back apart.

 

I hear you there Dave. My spark Plug Wires and Cap and rotor are going on 5 years old. They are motorcraft though, and you can clean the carbon from them up to a point.
I always try to buy motorcraft parts when I can, as they seem to be the last line of defence with quality. Napa is not bad as a second choice. I avoid Autozone like the plauge. Oriley's is good around here for buying motorcraft parts that my dealer doesn't stock, but that's about all I will buy from them as well.

When fordfreak took the carb apart he probably knocked loose the obstruction in the first place. I've had a sticky float before, and just whacking the top of the carb lightly with a screwdriver handle did the trick.

If the bottom of the carb was coming loose, it might be a good idea to throw a carb kit into it. It will vibrate loose again after awhile. You can use blue loctite on the lower threads to help keep it from vibrating loose as often. Don't use the red loctite as you will never get it apart again.

 

I had the same thing happen as the OP after I replaced the fuel filter with a "new" Fram part.The only difference is that my Bronco caught fire.I had an extinguisher as that was my second vehicle fire.That video broke my heart.I just had my third fire in my van as the foil backed heat sheet(supposed to be resistant to 2000 deg.) that I lined the inside of my engine cowl with caught fire.I carry a 3 lb extinguisher in every vehicle.

 

That was rough to watch, made me cringe!!

 

Fordfreek, you can plug your external bowl vent on the carburetor if your evaporative emissions equipment (charcoal canister) isn't hooked up.

Like the other posters have said, the problem with the YFA is that it's pretty sensitive with the needle and seat. All it takes is a little bit of sludge or dirt to jam the seat open and the truck runs pig rich, and like you've had happen, gas will come out of the external bowl vent if not plugged.

You've still got the internal bowl vent on the carburetor next to the choke plate, so no worries about venting issues.

I'll be willing to bet before you took the carburetor off, there was enough time for the gas to drain out and take some of the gunk with it. It probably also knocked some of it loose when you took it off the intake.

You say you tightened the four upward facing screws that point to the air intake... I think you mean the throttle body screws. Those four on the underside are what holds the throttle body to the carb.

If you've had this happen once (and you have), best thing to do is to put an inline fuel filter on your rubber fuel line just before the mechanical fuel pump.

All the 80 to 86 300's have a mechanical fuel pump that mounts to the driver side of the block. No electric pump. The rubber line you should tie into is down next to the motor perch right at the fuel pump. When they switched to EFI for the 300 in 1987, that's when the electric pump for the 300's came about.

The other thing with the Carter YFA is the accelerator pump. It reads the load on the engine with vacuum (and it is mechanically actuated too) and meters how the gas flow should be based on load (load being low vacuum under acceleration). If the accelerator pump diaphragm gets dry and cracks/tears or just tears from usage, then the truck will also run pig rich, but you shouldn't have flooding out of the external bowl vent.

Carter YFA Carburetor Rebuild Part 1 of 4 - YouTube

At around 12:20 is when he pulls the accelerator pump out of the carburetor. You can see how horribly stiff and dry that one is. He also has a notice about not letting the carburetor sit without gas.

It wouldn't be so bad if they didn't put deathanol in the gasoline. Ethanol attracts water and forms a nice sludge that can gum up carburetors. Ethanol also has the ability to dry out rubber. So you can imagine what kind of havoc this causes to rubber fuel lines and accelerator pump diaphragms.

My only chief complaint about the 300 from these years, with the stock intake and exhaust and the EGR, is that if gas happens to leak from the fuel inlet or from the external bowl vent, you'll have fuel dripping down onto a nice hot EGR base plate. As soon as the gas hits it, it turns to vapor. It would've been nice if Ford had clocked the EGR plate a little differently, or provided some sort of heat shield for the EGR from the fuel lines.

 

That's meant as an air inlet only. The carb gets fresh filtered air for the bowl from that vent. How is the expanding vapor going to escape when the truck sits after it's shut off?

There is a rubber seal hooked to a flapper valve over the vent hole you speak of to prevent vapor from exiting the carb that way. It acts as a one-way valve. This causes the expanding vapor to go to the charcoal canister. The only way the carb can vent properly is to have BOTH of those open.

Think of it working the same way as a evaporative emissions non vented gasoline cap. The non vented gas cap still lets air into the tank, but will not let it back out, (or vent) the same way. Expanding vapors have to go to the charcoal canister to be vented. People have made the mistake of closing off the vents to the tank on the charcoal canister side, or putting the wrong gas cap on their vehicles. This can cause the gas tank to fail, implode or burst at the seams.

If you block the carbs charcoal canister vent, there is a chance of the seals failing on the carb due to excessive buildup in pressure.

 

We're talking about the flapper being on the internal bowl vent next to the choke, right? As the external vent going to the canister is what allows the gas fumes through to the charcoal canister.

At 5:39 of the video that I posted in my previous post, this one:

Carter YFA Carburetor Rebuild Part 1 of 4 - YouTube

You can pause the video and see there is no rubber flapper blocking the internal bowl vent. 6:47 also gives a pretty good shot.

The external vent doesn't have a flapper either, to my knowledge, as I've actually had the vent fitting for my charcoal canister vent come out of the body of the carburetor. It has a mesh screen that might be able to stop something the size of a small spider going through, but that's it.

My carburetor vents just fine with the external vent plugged, and I've had it plugged for months now.

Not saying pressure can't build and problems arise... but I just don't see how.

The charcoal canister and the evaporative emissions are meant chiefly to allow the motor to pull the gas fumes from the tank into the motor for internal combustion, rather than venting them through the cap and into the atmosphere like older models. This also assists the gas tanks from building pressure when they expand and contract with temperature differences in the air and seasonal changes.

Not saying your wrong, and not saying that some models of YFA or YF can't have that flapper, but... no flapper on the one in the video and mine vents just fine.

 

It's internal of the carb. Look at the top left in this exploded diagram. It's next to the vent rod, marked flapper valve.



The primary function for the evaporative emissions system is to keep the gasoline vapors from venting to the atmosphere. The charcoal canister stores the vapors untill they can be purged and combusted.

That's why the venting of the gas tanks and carb on these models are closed systems. It alows outside air into the system, but not back out the same way.

 

The flapper valve is for the external bowl vent?

I found the exploded non-feedback version of the YFA as well. I noticed that yours was the feedback version with the solenoid so I had to look up the other one to see if it was the same with non-feedback models as well.



Either way, I'm going to get a good look at the inside of a YFA as soon as I manage to get another one I can pull the air horn and choke assembly off of so I can fix the fast-idle cam on mine.

Maybe I'll get another YFA that I can rebuild and take some pictures of (inside and out for reference of course), and just swap the rebuilt one onto my truck. The one on my truck presently seems like it's jetted a hair too lean for what my truck wants.

The fast-idle cam link is missing on my YFA.