New Fuel Venting - Carb Adjustment?

[mpboxer]

I have a 73, 302, 4 barrel Edelbrock. Installed a new charcoal canister and all new vent lines to both tanks. Once truck was warm and only at idle it sounded like the engine was stumbling. Exhaust smelled rich. Checked for vacuum leaks and loose plugs etc. After adjusting my mixture screws out slightly engine leveled out and idled nicely again. Would this new working vent system cause more "fuel/vapors" to enter the carb requiring more air?

Side note, does anyone have a better idea as far as type of tubing I can run from the charcoal canister and pvc to air filter? The heater hose looks bulky and doesn't do it for me.

 

[jckkys]

The charcoal canister draws vapor from the float bowls after the the engine is shut down. It has no effect on the air/fuel mixture. On an AFB or what Edelbrock calls a performer, the bowl vents are in the top cover just outboard of the step up rod covers. Any vapor from them is drawn down the venturis when the engine is running. The air in the gas tanks cools down and contracts after shut down pulling vapor into and trough the canister and back into the gas tanks.
I think you mean PCV or positive crankcase ventilation. The hose should be 3/8" ID PCV emissions type hose from the front nipple on the carb to the PCV valve. This never runs to the air cleaner. Any parts store has it. The PCV hose goes to one valve cover the other valve cover gets a breather hose form that valve cover to the air cleaner. These are 5/8" ID emissions type hose.
I just saw your photo. The large hose to the charcoal canister should be 1" corrugated aluminum flexible tubing that only runs from the back of the air cleaner to the canister. That cheesy after market air cleaner likely does not have both a breather nipple and a vapor nipple. The original Bronco air cleaner does. These cheap shiny air cleaners are junk.

 

[mpboxer]

The charcoal canister...

Thanks Jckkys. Yes, I meant PCV. I have the routing correct as you described. So you’re saying the carb adjustment has nothing to do with my charcoal/evap setup? Any idea what to use in-leu of the one inch heater hose going to the charcoal canister?

Yeah, I used a T fitting (seen in photo) to route both the charcoal and pcv tubes to the after market air filter.

If I could run the stock air filter I would, but I have a 4 barrel intake/carb.

 

[73azbronco]

I dont think your pcv setup is right.

I dont think you should have the block venting to the evap canister.

How is that run, to vacuum under carb or just outside the air filter in the air cleaner, no real vacuum?

 

[DirtDonk]

You can't interconnect the PCV and the EVAP system. Two separate systems.
The canister should NEVER be connected to anything with direct manifold vacuum that is not controlled by a computer. A standard system with a carburetor is simply "vented" into the air cleaner housing ahead of the carburetor. Not behind it where there is vacuum.

Paul

 

[mpboxer]

I currently have the canister and “fresh air” side of the pcv going to the air filter. That is pictured on the passenger side photo. My driver’s side valve cover has the pcv valve going to the base of the carb.

I guess the question now is how to hook up the canister and fresh air side of valve cover with an after market air filter? Thanks for all the help!

 

[Justafordguy]

The factory air filter housing will fit an aftermarket 4bbl carb/intake no problem but you can buy add on fittings for the base plate of the aftermarket air cleaner also. You would just drill another hole and bolt the second fitting on the base plate.

 

[mpboxer]

The factory air filter housing will fit an aftermarket 4bbl carb/intake no problem but you can buy add on fittings for the base plate of the aftermarket air cleaner also. You would just drill another hole and bolt the second fitting on the base plate.

Good to know! So where I went wrong was connecting the pcv fresh air to the charcoal canister via a T and having them both run to the air filter.

I should just have each one individually run to the air filter?

 

[gr8scott]

I should just have each one individually run to the air filter?

Correct. Or replace the fresh air intake nipple with something like this:

https://www.summitracing.com/parts/knn-62-1030/

 

[mpboxer]

Correct. Or replace the fresh air intake nipple with something like this:

https://www.summitracing.com/parts/knn-62-1030/

10-4, and thanks for the link! I think I may do that. Much cleaner looking solution.

 

[DirtDonk]

And they each go to different sides of the filter too by the way.
The PCV fresh air is "inside" the filtered area so that only clean air gets sucked back through the tube and into the engine.
Whereas the charcoal canister's vent can simply go to any area "outside" of the filter itself. Because it's not in need of filtered air, it's simply letting the gentler pull of the intake are pull what fumes are in the canister into the engine through the normal intake process.
You don't need, or want a strong pull on the canister vent line. Just the fact that any vapors that escape on their own will get sucked into the engine and burned, rather than actually encouraged to come up from more vacuum being applied.

Any time you T into the PCV you have more vacuum than would be desirable for the EVAP system. You're not only pulling the fumes into the crankcase where you don't really want them (even though they eventually get sucked back into the engine and burned in combustion) but you could conceivably pull raw gas up through the vents and into the charcoal canister. Where it would harm the charcoal media and create a too-rich vapor getting into the air filter area.

I can't say these are why you're having tuning issues, but it won't hurt anything to put them back the way they should be (separated) and see what happens. You might get lucky and that was the issue in the first place.

Paul

 

[mpboxer]

And they each go to different sides of the filter too by the way...

Thank you for all the info Paul. I ordered a breather cap to keep things simple. Now I just have to find 3/4” ID tubing to connect that canister to my air filter. Does Wildhorses sell that size metal corrugated type?

 

[mpboxer]

Thanks to a previous post on here. This looks to be the part number. In case it helps someone in the future.

 

[jckkys]

There is no reason not to use the stock EB air cleaner. It's not a 2 BBL air cleaner. It's the standard 5" diameter carb mount as most other air cleaners. I've used 4BBL Holleys, AFBs, and 4100 Autolites. Even GM quadrajets work with OE Bronco air cleaners. Where does the idea that OE Bronco air cleaners are only for 2BBL carbs come from?
I described both the PCV and vapor recovery plumbing. One connects the air cleaner to the charcoal canister, the other runs from the front of the carb to the PCV valve on one of the valve covers, I never implied they are connected. The hose in the other valve cover gets filtered air from the air cleaner. The vapor hose is corrugated aluminum like this;http://www.mustangsunlimited.com/Mu...To-Carbon-Canister-Hose-1970-1973-Mustang.axd. The PCV hose is 3/8" ID PCV hose. The breather hose is 5/8" emissions hose. None of these are connected to each other. A filter in the breather cap will work on the right valve cover. The AFB has a very convenient 3/8" nipple in the front between the idle mixture screws. Just run a hose from this to the left valve cover where the PCV valve should be.

 

[73azbronco]

problem with stock cleaner is if you use headers, the lower bracket is a pain to figure how to mount onto a stud, which no longer exists. Or has room for. Stock bolt with threaded head wont fit. Still trying to figure that issue out, but for now im using an aftermarket to get me out the door.

 

[blubuckaroo]

Even if a connection point isn't provided on an aftermarket air cleaner for connection to a charcoal canister, one can be added. I drilled a hole in the base with a unibit and added a nipple I got from the auto part store vacuum fitting section.
I doubt it's as effective as the one on a factory "enclosed type" air cleaner, but all it takes is a lower atmospheric pressure than the fuel tank. Mine seems to work just fine.

 

[DirtDonk]

The EVAP fittings supplied by the air cleaner manufacturers back in the day (and maybe still available?) were just simple rectangular plates with a 5/8" or whatever host fitting in the middle.
The plate was tall enough to be clamped between the base and cover of the air cleaner housing and sat there next to the filter element.

As said, not as effective because the filter is wide open. But at least it was reasonably good at pulling the fumes out of the canister when the engine was running. Without a big buildup left over to exit the canister while the engine was off, the fumes, if any, would be kept to a minimum.

Paul

 

[DirtDonk]

Oh, and even though I can't actually justify it as a "recommended practice" I ran my stock air cleaner housing without that support for 20 years as a daily driver and off-roader with no issues.

The rivets on the housing canister rusted out and the bracket just separated, so there was nothing to bolt to the exhaust support bracket. This happened when the vehicle was about maybe 7 or 8 years old, and I just ran with it.

Paul

 

[jckkys]

A support can be fabricated from steel strapping to work with any exhaust manifold or headers. The OE air cleaner is far superior to any after market junk. I don't think boxer said whether he has the OE air cleaner, but they are available.

 

[gr8scott]

The OE air cleaner is far superior to any after market junk.

I wish someone made an aftermarket reproduction. They'd sell. I'd buy one. The ones on ebay are rough.