Fair enough.

I have always been driven to know in how stuff works not just the how but also the why and the theory dictating it all.

As a kid I drove my parents nuts cause if I could take something apart when they were not looking to see how it worked it was quickly in pieces.

As a young teenager I quickly became interested in cars (like any normal young man) as they were the most complicated piece of kit available to the general public. And they had just about every engineering discipline applied to them. Hydrodynamics, Structural,Mechanical, Aerodynamics, etc etc.

I was never strong in the arts or language arts , I can orate with the best of them but the written word not so much. Ask me to create a literary master piece of a great work of art or play a musical instrument forget it. As my Dad used to say give me a pen I'm a blithering idiot (I have hand writing like an engineer also lol) but put a wrench in my hand or set calipers and a calculator and I'm Leonardo DaVinci.

I have always had the ability to look at piece of equipment disassemble it in my mind see the threory behind it's operation and reassemble it.

This naturally led to a multi discipline engineering degree from Western. Where I was involved in several award wining projects. I was recruited by Ford Canada upon graduation in the mid late 70's.
I spent some years at Ford Canada in their Engineering dept working on fuel management and emission systems for the Canadian and US markets. Working for Ford was rewarding but wrought with politics which I found distasteful and most of all frustrating.
There was nothing worse than to see poorly engineered designed kit go out the door cause some yahoo did not want to admit they screwed up and went to any lengths to cover it up.


An opportunity presented it's self out west in the oil and gas sector in Alberta. It appealed to me due to the lack of bureaucracy and the say it like is environment. If something was f'd up you could say it was F'd up and every one pulled together to fix it with no worries about people trying to protect their fiefdoms or cover their a$$ cause we all know we all screwed the pooch on occasion and goal was to provide the best product possible balanced to a profitable cost. I now mostly consult and when they crop up project manage civil construction projects.

I'm pretty detail oriented and sort of have a black an white attitude at times. It either works or it does not. It's either F'd up or not.

I don't suffer fools or idiots well and can be a bit prickly when they are present, not though any air of malice but a lack of patience for not having basic common sense.

I have 3 kids 2 boys from my starter marriage and a very strong willed extremely smart daughter that is going to drive some poor SOB nuts one day lol.

I have been wrenching on vehicles in my spare time for over 40 years usually always looking for more power better efficiency and higher reliability. And just like when I was a kid fixing them was not just enough I want to know the how the why and theory behind the operation and the reason of why it was done that way.

I have restored many vehicles from muscle cars to Lincolns to trucks to military vehicles in my spare time. Doing most of the work myself short of paint (except for the mill vehicles) That's the great great thing about mil vehicles the paint does not have to be perfect and in many cases it was not. Heck in the feild the stuff was painted with a paint brush and a bucket at times.

I have pretty much always driven Fords as has most of my family going back to the early 20th century. I migrated away from Ford for cars when they ceased selling RWD sedans. At that point I moved to Mercedes. I'm not a fan of FWD or lateral mounted engines.
But for trucks it's Ford.
Even then I restored a couple Chev CUCV's and have another one sitting at the acreage in the cue. Let me tell ya there is reason Ford has been the best selling P/U truck in Canada for over 50 years........

I'm not a literary guru by any stretch and as I have stated before, if my posts come off as arrogant and condescending that is not the intention as I'm anything but. Expressing technical stuff no issues communicating inflection or tone through the written word I fall on my face and am the first to admit it. So I apologize in advance if I come off as an a$$ at times.


Hope this answers your questions

 

Yes, it answers a lot of questions. And I see a lot of similarities between us, although I didn't finish my engineering degree but shift to math and physics. In any event, I'm sure glad you are at FTE, and specifically on the Bullnose forum. We need your understanding of things to augment ours. So if I, or the literary "we", push back on something you say please don't take it personally.

 

Very nice post matthew, I'm kind of like that too. I like to read the technical posts

on FTE they have alot of great information. As far as air cleaners go I am like Gary

in that I like the factory look even if I have to change something to what I think the

factory should have done.

 

Why not leave it as it is? The Bullnose trucks (like most 1980s vehicles) used an electric bowl vent solenoid or a vacuum-operated thermostatic bowl vent valve that would effectively close off the external bowl vents when the engine was running. (Now I understand why!)


Well then, why did Ford bother at all with the mechanical bowl vents that closed above idle? It seems to me that it would have been a whole lot easier and cheaper to simply close off the external bowl vent(s) altogether.

Ford went through some trouble installing a mechanical vent to keep *some* of the fuel vapors out of the air cleaner when the engine was off. And then they went through even MORE trouble and expense later with the carburetor fuel bowl fitting(s), hose(s), and valve(s) for the same reason.

If all of those fuel vapors from the fuel bowl could simply evaporate through only the air cleaner vents without any ill effects, why did Ford bother? And you can't say because of "emissions regulations," because the air cleaner vents were ALWAYS open, even with emissions regulations - Ford never had a way to close off the air cleaner vents under certain conditions like they did with the external bowl vent.


Isn't it true that if the fuel bowl bowls are vented to the charcoal canister (except when the engine is running), the fuel in the carburetor fuel bowl won't evaporate as quickly? Plus, doesn't the captured fuel vapors in the charcoal canister from the fuel bowl (and gas tank) get used later, improving fuel mileage a little?

 

Most of that stuff above is not what I had a problem with. I did not like your statement
"The engine always has a vacuum except when going immediately from idle to WOT or near WOT that is why the accelerator pump is there".

But I think it's just a wording problem. When I hear the word "vacuum" in relation to a engine, that would be suction on the hoses and other components connected to the intake that we can utilize to do different things. Like I mentioned and you brought out, there will always be "vacuum" or a pressure drop in the engine, but at wide open throttle it will be so low a regular 0-20 vacuum gauge is barely going to read it.

I think it's also better to "dumb down" some of this stuff so more people understand it (including me). And we have several young people in here that have never seen a carburetor except on these old trucks, and we have had several posts where we have to coach them on the proper way to start one. So that's why I like to say for all intents and purposes, there is no vacuum at WOT.

 

Thank you, Matthew, this says a lot. I've seen you around on FTE in the years past but you've never really stayed around long, at least not in the forums I generally hang out in. Maybe you're annoyed by the user-originated questions, dunno.

A bit about what we have here in 80-86, at least from my own perspective as a mod who reads most everything here... about half the population is aged 50+ with some guys having tremendous amounts of intelligence, training, and/or practical experience in their chosen fields of interest, including restoration of these things.

The next 33% or so are aged mid-20s through mid-30s or so, and some of these guys have got decent practical experience with technology of this era, some are learning, and some are clueless (never had a carb & choke before) and learning.

The rest of the population are the teenagers and kids who buy this stuff because it's cheap and aren't so interested in the details of how it works but just want a truck that works for them, maybe with some chrome add-ons or other lightweight mods. These are the kids where you sometimes have to tell them to RTFM the Owner's Manual where it explains how to set a choke in the winter by flooring the accelerator once, but lots of these people don't have such manuals and for some reason won't go purchase one on eBay.

~~

A bit about myself, probably the most I've said about myself online in a long time...

I was also the kid who liked to take things apart just to see how they work, I could usually (but not always, mechanical typewriter comes to mind) put stuff back together and make it work again. Prolly not so much into the how & why as you, though, but more below.

I watched my father and his friends build stock cars/muscle cars in the garage in the 60s and 70s - Mustangs, Firebirds, Corvettes, that kind of stuff, and so I was already into this stuff by the time I got my own first car as a 16 yo kid, a 1970 Mustang fastback 351W FMX... replaced the engine with a JY variant from a 71 LTD, swapped in a limited-slip pumpkin, converted the front non-power drum brakes to the power disc variants (a sucky job in the cold weather, frozen concrete is no fun to lay on) those were the most major operations I made to that car as a teenage kid.

Also wired in an LCD clock I got from Radio Shack, that was cool as it was all digital electronic with cool, dimmable blue digits and what-have-you. This was pretty much my first experience with Ford wiring and their colors, turns out much of that hadn't changed even into the 90s.

But someplace around Freshman year of HS is where I got big into computers, this was the Apple & Commodore days of the mid-70s. You see, my mom's brother had been getting me into electronics/computers, TV & radio since I was around 12 yo in early 70s, I was drawn to that stuff, too. And then when the Apple II came out, man I fell in love with that! It was pretty dang easy to write programs that produced moving colored objects on the screen, controlled with a handheld joystick or rheostat. And, like you, my mind wanted to go farther and farther into the hows and whys of how it all worked, down to the IC circuits and how those things operated.

But at the age of 18 or so is when I took a wrong turn in life and alcohol & drugs were controlling me more than anything. I had graduated HS and gotten a job in a data processing company working on "real" computers (DEC PDP & VAX) which furthered my interest in computers, but the alcohol & drugs were taking up most of my drive and ambition and I never pursued that stuff seriously.

Fast forward about 10 years when I came out of that stuff... I quit my job, rented out my house, and moved 75 miles north to attend ColoState U as a full-time student Fall of 1990, something around 27-28 yo and I felt OLD lol. I initially wanted to study how to use big (IBM) computers in business but it's where I discovered the Internet, UNIX, and, later, the WWW, and decided to spend my life there, instead. And I'm still there, I'm a Linux sysadmin who got out of the newspaper industry last June and am hoping to find myself in the cable TV industry hopefully shortly. (EDIT: Which is kinda odd... I began my post-college life in the cable TV industry, built AT&T Boadband's first-ever WWW serving infrastructure then did Satellite TV set-top box engineering support, then the (dying, really badly) newspaper industry... and now back to cable TV, we'll see.) Never been married, no kids.

Around 2005 is when I got my first pickup truck, a 1981 F350 to haul firewood to heat my house. I had watched my father & brother rebuild engines, now it was my turn. Found a pretty good local machinist specializing in 60s/70s era Ford engines, he taught me a lot. Also got a friend with whom I used to work, this guy ran machine shops and built engines in the past until he hurt his back (surgeries, screws, steel rods) and now he does computer networking stuff as a job, he's just finishing a 5+ year frame-off rebuild/restomod of a 1971 Camaro.

But those guys are my primary mentors on engine internals.

My most recent car activity is focused on 92-95 Taurus SHO with a bit of mid-90s EFI 351W Bronco as it arises (my brother's). Yes, the sideways-mounted engines and EFI were intimidating for a while, and I got a big jump-start on that stuff from some people here on FTE.

My mom died about 1.5 years ago, still dealing with that.

~~

But, so, let me ask you... are you one of those antisocial types of guys? Would you accept an FTE Friend request, for example? Or do you stay away from that kind of stuff? There are guys here who are like that, I don't really care, am just curious is all.

How do you feel about being wrong? Myself, being in IT, I have learned that it's OK to be wrong as there is no way possible for any one person to know absolutely everything about how all this hi-tech stuff works, just can't be done. I don't LIKE not being right, but I'm usually humble enough to be able to admit when I'm wrong and apologize for it.

It sucks about the fiefdoms & CYA politics but many large organizations operate that way, or so it seems.

Yes, I see you have troubles with writing, that's OK as we can still usually get the gist of what you're saying. Myself, I've always been able to write well but can't add numbers, mathematics was never my strong suit and so it's odd how I'm so drawn to computers & electronics but that's the way it is.

I have a personal distaste for those who apparently intentionally write poorly - lack of capitalization, commas, textese shorthand (id im ill for example) I have to be in the right mood to be able to respond to those kinds of posts, I usually ignore them because I'm too irritated at trying to comprehend stuff.

And I have been known to go off on people in some of these forums sometimes, requiring a supermod or admin to clean up after me. It's happened twice now where I've really foamed at the mouth in public at some people who really probably didn't deserve what I fed them but their attitudes that I perceived in my brain precipitated that (don't get me started on Millenials and some of their values).

But in general, I try and help people where I can with what I know.

~~

Anyhow, that's enough about me; thank you for being here (it can take a long time to write some of this stuff), I hope you stick around.

 

Provided the whole system is working correctly, who here has tested their BV solenoid for function and proper operation ? I bet almost no one has.
This system was very trouble prone at the best of times and is completely over looked 99.99% of the time vehicles will never have had it tested for function in the life of the vehicle, plus diagnosing and function testing it almost impssoble many times due to the complete lack of information available in the in factory shop manuals..

And that is exactly what they did later on delete them . Originally the pre emissions bowl vents (2100 4100) are just vented to atmosphere they were there to help alleviate hot idle issues. It was a bad idea then it is a bad idea now. It was little more than disk on an arm that sort of sealed to the top plate of the carb. These are known for leaking fuel letting crud in to the carb and they don't exactly seal so they throw off the pressure in the fuel bowl.



OK everyone needs to get off this the external bowl vents keep vapours out of the air cleaner when the engine is off BS already.

The only carbs this is true for is the early 2100 and 4100's as mentioned above, We have been over this multiple times that is not what they are there for that is not how they work that is not what they do.
I wont even entertain answering these questions after this CAUSE THAT IS NOT THEIR PURPOSE,

Again for FOR THE LAST DAMN time they are there to alleviate hot idle issues messing up the fuel air mix.



See above it was to help control hot idle fuel mix. If you end up with high under hood temps that means evap in the carb accelerates putting a crap load of extra fuel in to the in the induction system.
The hot idle compensator will adjust for this if equipped but what does it do to the emissions ? you now have a rich mix in the carb and at the tail pipe HC goes up and CO goes up not good for the emissions profile.


No the fuel bowl is vented to the charcoal canister when the throttle is at rest regardless if the engine in running or not.

The carb's bowl is open to the charcol canister when the engine is off due to design not function.

When the engine is idling the the bowl vent can be evacuated to the charcoal canister during periods of hot idle this will trap and delay the return of these vapours to the engine preventing an overly rich condition, this will allow time for other components in the emission system to pick up engine speed and cool down the under hood temps.


The bowl being open to the charcoal canister is a matter of just how the system works OPEN AT REST and HAS NOTHING TO DO WITH VENTING WHEN THE ENGINE IS OFF. The only carbs that did that are the fore mentioned 2100 and 4100.

Fuel vapors WILL NOT and CAN NOT defy the laws of physics to force their way in to the charcoal canister when the engine is off.

Saying the fuel vapours will vent in to the charcoal canister through the bowl vent when the engine is off, Is equivalent to saying water flows up at night and down during the day, both are equally ridiculous.

 

Saying "for all intents and purposes, there is no vacuum at WOT" is an incorrect and wrong statement bottom line.

You can not make blanket statement like that as their are lots of engines that will have substantial vacuum at WOT such as the stock 300 I6 and many others as well.

And by telling any one that is NOT coaching them it is telling them false information.

Saying there is greatly reduced vaccum at WOT is the correct way to state it..

 

The pre-emissions external bowl vents (Autolite 2100/4100) were vented to atmosphere to help alleviate hot idle (and hard hot start) issues, and then they were vented to the charcoal canister for the same reason in the later years. But what did Ford do about the "hot idle issues" when these vents were eliminated in the years between?


Alright, you asked for it...

WHAT is causing the "hot idle issues?"

Excessive fuel evaporation from the fuel bowl...RIGHT?

WHERE is all of that evaporation that "messes up the fuel mix" going to end up?

Inside the air cleaner...RIGHT?

If the air cleaner is filled with excessive fuel vapors, WHAT does that do to the idle mix?

It makes it richer...RIGHT?

And, if the mixture is rich when you try to start a hot engine, what happens?

You will experience hard hot starts...RIGHT?

So, if external bowl vents will alleviate some of the excessive fuel evaporation and eliminate hot idle (and hard hot start) issues - whether they are open to the atmosphere or vented to the charcoal canister - WHY would you recommend plugging them?


No, not for the Bullnose trucks and other 1980s vehicles. The bowl vent solenoid (or the later thermostatic bowl vent valve) closes, preventing the fuel bowl from venting to the charcoal canister anytime the engine is running.

The bowl vent solenoid will close and seal the fuel bowl hose as soon as the engine fires electrically, whereas the thermostatic bowl vent valve does the same thing using manifold vacuum - which is produced as soon as the engine fires.

With either valve, the carburetor fuel bowl vents are CLOSED any time the engine is on, including idle.


No, the fuel bowl does not vent during periods of hot idle for the reason I mentioned above, at least not for the Bullnose trucks and other 1980s vehicles.

So, that means your whole explanation for the reason behind the external bowl vents is flawed somewhere along the line.


You are contradicting yourself. Either you are wrong above, or wrong below. According to you in the statements below, the fuel vapors will vent from the fuel bowl to the charcoal canister when the engine is at rest "regardless if the engine is running or not" and idling. Wouldn't *that* defy the laws of physics and be equally "ridiculous," like you said above?


The statement above is incorrect. Because as I said before, the fuel vapors from the carburetor can not vent to the charcoal canister when the engine is running (or idling) because the bowl vent solenoid (or the later thermostatic bowl vent valve) closes, which prevents the fuel bowl from venting to the charcoal canister anytime the engine is running.

And you say those fuel vapors can not vent to charcoal canister when the engine is off (at rest), either...because of the laws of physics.

If that's true, then WHY did Ford route a hose from the carburetor fuel bowl to the charcoal canister, and WHY did they insert the bowl vent solenoid (or the later thermostatic bowl vent valve in the fuel bowl hose to the charcoal canister to allow and prevent the venting of the fuel bowl ?

 

 

Well said, Chris. There is no proof.

 

Seriously

Ok I will try to simplify this down this further not sure how but I will give it a shot.

Ok once again they got rid of the external vented on the 2100 and 4100 bowls cause it was

A.
Messing up the AFR (Especially on the non valved ones) due to the float bowl NOT being at the same pressure as the the inside of the air cleaner. And affecting venturi metering due the pressure differential in the float bowl and air cleaner.
All later carbs that had the non valved external vented bowls were blocked off. Even carbs rebuilt by the big companies blocked them and If I recall correctly there is even a Ford TSB stating to do this on earlier carbs when the carb is rebuilt.

B.
The Valved vents do DO NOT have an air tight seal against the carbs top plate.
This still allows for a pressure differential in the float bowl messing up the AFR. But to a lesser degree than the non valved ones.


C.
At idle the vents on ALL are open. This is a problem for dirt ingress.
The inside of the air cleaner will ALWAYS be at a lower pressure than the atmosphere. No matter how good the air cleaner or the air filter it takes air pressure to move the air through the media.

So you have a bowl vent open to atmosphere and a path to the inside of the air cleaner through the bowl vents. This will pull air through the external bowl vent in to the float bowl and out the vents in the air cleaner. Since these are on the front of the carb and in the air flow from the rad fan that also means they are sucking debris dirt and dust in to the float bowl. It will then be captured by the gasoline and fed through the carb potentiality plugging passages and orafices or settling in the bottom of the carb. This WILL in time lead to blockages.
You are in effect now using the float bowl as a wet filter.

If you have torn down a 2100 or 4100 that did not have the vents blocked off And has been in service for along time or operated in dusty condition they are ALWAYS full of crap and debris.


When they went away from these external vents they lowered the opening temp of the hot idle compensators in applications that had them. Otherwise they did nothing.

I have stated time and time again why the bowl vents should be capped.

TO ALWAYS KEEP THE FUEL BOWL AT THE SAME PRESSURE AS THE AIR CLEANER.
This is to insure that fuel in the bowl has the same pressure feeding the venturi as it generating..

Hot idle and hot start ARE NOT THE SAME THING.

You basically have to boil the carb dry to get a hot start, that is what a hot start is. Hot starts happen when the carb heats up after engine shut off due to latent heat in the engine boiling off the fuel in the carb.

You are going to have to crank the engine to fill the carb and clear the intake of the rich fuel mix any way.

Plus it's a carb, potential hot starts are a penalty of using a carb simple as that . Why do you think Ford and others for that matter used phenolic and plastic spacers under the carb ? To mitigate hot start issues by insulating the carb from the engine. That is how you mitigate hot start issues.
Vent the bowl all you want heck take the top off the carb you will STILL boil off the fuel in the carb and done ABSOLUTELY NOTHING to alleviate the hot start.




This is wrong so very wrong. The bowl vent is open idle it is the only time it is supposed to be open. IT IS DONE THIS WAY TO PREVENT HOT IDLE.

I think you better get your hands on a mech controlled bowl vented carb and have a close look at it. I have even shown this with pictures on a previous thread with the vent pulled apart on a emissions Holley that was fitted to a Ford with EVAP.


Your understanding of the operation the system is flawed. That is what is flawed.

The Bowl vent should ONLY be open at idle that is the correct operation of the system.

The TVV opens when the engine warms up ( about 90F) other wise is it closed.

Do you even know what they moved to an electrically controlled vent solenoid valve ? Why do this when the mech one does the same thing for lower cost ?

The reason for the electrically controlled one was to have more accurate idle fuel mix and. I posted the CO to AFR ratio table, very small changes in AFR can have a big impact on CO and in turn emissions.

With a mech valve it was always open at idle this allowed for the fuel bowl to be atmosphere pressure or near it or possibly even below it in malfunction. Ok that is fine the pressure differential is minimal between the inside of the air cleaner and the fuel bowl. But it is still there affecting the delivery of the fuel in the idle circuit by raising the fuel level in the emulsion tubes, thus richening the mix.
The idle mixture screws do NOT affect the AFR in the idle circuit they adjust the AMOUNT of it delivered.

So now you have variations in the idle circuit AFR depending on air filter restriction at idle. What happens if you have a partially plugged up filter? The AFR is now richer than desired affecting idle emissions.

So how do you solve this? Block off the carb vent. But then how do you negate hot idle issues ? Well how about if you have a valve that will open when under hood temps are conducive to hot idle...... like when the AC is on.....or the engine high temp idle is active.

And there in a nut shell you have operation of the elec controlled bowl vent.

When the vent is open hot idle fuel vapour can be sent to the charcoal canister and sequestered and sent back to the engine at a later time. IE acceleration.

The canisters are purged at start up on a cold engine where the extra hydrocarbons are appreciated in a cold start.

On a hot start or normal engine temp operation the canisters are purged at a given manifold vacuum IE during acceleration where the extra hydrocarbons are again appreciated and do not affect measured emissions.

These systems are ALL now 30 years old these old mech and electromechanical systems were trouble prone when new and usually all fell out of adjustment or stopped working properly after a few years. Now 30 years on ALMOST none of them function correctly.

They were a bitch to diagnose and trouble shoot when new and Ford even had a special tool used for testing and trouble shooting them. Do you have the tool ? I don't have the tool. And then even then try to find the testing procedure or even the proper emissions shop manual with all the specs for that matter.

This was one of those things that just about everybody did a better job with. Ford by far had the worst most unreliable convoluted never worked properly EVAP systems on the market it was a complete engineering F up. GM had a much more simple robust reliable set up hence the 15 pounds less of vacuum hoses valves an crap under hood on GM products.

No cause you have a little some something called vacuum when the engine is running. That is what is used to vent the fuel bowl to the charcoal canister.




Again flawed reasoning cause you do not properly understand the operation of the system.


Hey if you can get the fuel vapour to enter the canister when the engine is off you have just solved perpetual motion.

The canisters media is a restriction to air flow. The fuel bowl is at atmospheric pressure when off as it is vented in to the air cleaner the inside of the canister is at atmospheric pressure as there is no engine vacuum to purge it. . So how exactly does the fuel vapour pass through or in to a restriction to flow with no pressure differential ?
Care to answer that one. ?

Or how about this one if the fuel is hot enough to be evaporating in to a gas that means it will be rising, and considering the charcoal canister is below the carb and in a much cooler environment how will the hot vapour flow down to a cooler environment. Care to answer that ?

If you can credibly answer these questions within the laws of physics you will have solved mankind's need for fossil fuels and are an your way to a noble prize and multiple billions.

Or even better. The TVV is closed when the engine is cold but open when warm (about 90F) But you say the vent solenoid is always closed when the engine on.. So when cold the TVV is closed when the engine is on the Solenoid is closed.
So you claim that it is there to prevent hot starts by venting the carb (which regardless is not possible). So Ford added all this crap and a rather costly
elec solenoid the extra wiring extra vacuum lines. When a phenolic spacer costing 1/10 as much would do the same job and better for that matter.

There is some erroneous information on line about the operation of the system. And if that is were you got it from....... well you can't believe everything you read on the internet.



Already answered see above.

 

I think *your* understanding of the operation of the system is flawed, Chief.

Here is a schematic of the Ford thermostatic fuel bowl vent valve from the patent office, which replaced both the electrical bowl vent solenoid and the thermal vent valve, which replaced the mechanical bowl vent. The description below contradicts all of your points above:


Patent US4456216 - Carburetor fuel bowl vent valve assembly - Google Patents

This invention relates in general to a vent valve for an automotive type carburetor fuel bowl. More particularly, it relates to a temperature sensitive one that is controlled by engine vacuum to prevent venting of vapors when the engine is running or the temperature is below a predetermined level.

A carburetor fuel bowl vent valve assembly consists of a one-piece plastic housing having a central partition with a central well defining a zigzag shaped path for the flow of fuel vapors from the carburetor fuel bowl to a carbon canister. The well contains a vacuum operated vent valve that is spring opened during engine-off operation to allow the storage of fuel vapors under engine hot soak conditions, and is closed by engine manifold vacuum during engine running operation so that the fuel vapors will be rerouted into the engine. The vent valve further includes thermally responsive means to close the vent valve during low ambient temperature conditions.

The normal objective in a vent valve of this type is to allow during engine hot soak conditions the flow of fuel vapors from the carburetor fuel bowl into the carbon canister to be adsorbed therein for storage during engine shutdown. During engine operation, this flow of vapors generally is cut off and the vapors generated vented internally of the carburetor to richen the air/fuel mixture charge.


This information falls in line *exactly* with what is written about the Evaporative Emissions system in both the Haynes and the Chilton's repair manuals.

 

You have interpenetrated this incorrectly.

Lets break this down.


"A carburetor fuel bowl vent valve assembly consists of a one-piece plastic housing having a central partition with a central well defining a zigzag shaped path for the flow of fuel vapors from the carburetor fuel bowl to a carbon canister"



This just saying what it is shape and that it routes fuel vapours from the carb to the Charcol canister.

The well contains a vacuum operated vent valve that is spring opened during engine-off operation to allow the storage of fuel vapors under engine hot soak conditions, and is closed by engine manifold vacuum during engine running operation so that the fuel vapors will be rerouted into the engine.

This is stating that during engine off (rest) the valve is off (open).
And "will" allow the passage of vapors to the charcoal canister.

This where you got hung up.

In an at rest sealed float bowl such as some 7200VV's that have an air cleaner vent that is closed during shut down and open during operation
The things stated above will happen this has been covered in previous posts.

But not in the 2150 or any carb for that matter that has other external vents, After shut down the system will be hot and the fuel vapours will be hot and wont go "down" to the charcoal canisters. Again laws of physics.

You still have not explained how this would happen.



The vent valve further includes thermally responsive means to close the vent valve during low ambient temperature conditions. It also includes seal locating means that retain the seal in position without stretching or deforming it.

Hot soak in the description is referring to the time after the engine shut is off
and the carb soaks the latent heat generated by engine that is no longer being carried away by the cooling system. It has nothing to do with hot start.


The normal objective in a vent valve of this type is to allow during engine hot soak conditions the flow of fuel vapors from the carburetor fuel bowl into the carbon canister to be adsorbed therein for storage during engine shutdown. During engine operation, this flow of vapors generally is cut off and the vapors generated vented internally of the carburetor to richen the air/fuel mixture charge.

Here is the "but" in this claim.

"The normal objective"

This frees it from being definitive that is what it is going to do or actually do.

The set up on the 2150's and most all other at rest externally vented carbs does not and will not operate as described in the patent application.

To have the system operate as described in the patent would have required fairly significant design changes to the 2150 and it's venting system.

Many times what is being sold as one thing is actually something different.
And no auto manufacture has ever been guilty of that especially if they can save a buck.....

 

That is correct. When the engine is not running, there will be no manifold vacuum. Which means the thermostatic vacuum bowl vent valve will be OPEN (usually, see below under "SUMMARY") - providing a clear, open path from the external vents, through the hose, and down to the charcoal canister, where the vapors from the carburetor fuel bowl will collect in the charcoal canister. On earlier carburetors with open vents, these vapors simply vented out into the atmosphere.


On all of the applications I have seen, a ported vacuum switch ensures that the canister purge valve turns on only when the engine has warmed up. And the vacuum source is usually ported vacuum, which means it only turns on above idle. This will help prevent hot start and hot idle problems because the engine can burn the extra hydrocarbons better when the engine is fully warmed up and and above idle.


The part number for the thermostatic vacuum bowl vent valve is E3TZ9G332A. The "E3" means is was originally designed in 1983, and the "T" means it was originally designed for a TRUCK application. Was the 7200 VV carburetor ever offered in a 1983 or later Ford F-Series truck?

My 1985 F150 with a Motorcraft 2150 carburetor had this particular valve (V-CBV on the vacuum diagram) inserted in the hose from the external bowl vent to the charcoal canister. I have the valve in my hand right now. If I blow through one end of it, the passage is clear for the two ends that connect to the fuel bowl hose. When I suck on the end of it, you can hear the valve CLOSE, which then blocks the flow. This simulates the closing of the thermostatic bowl vent valve when the engine fires - because manifold vacuum is produced - preventing the fuel bowl from venting to the charcoal canister anytime the engine is running.

Here is the vacuum diagram of a 1985 Ford F150 with a V8 engine and a Motorcraft 2150 carburetor with external (and air cleaner) bowl vents. You can see the thermostatic vacuum bowl vent (V-CBV) connects to the external bowl vent (BV), the charcoal canister, and manifold vacuum (MAN VAC):


And here is a picture of the thermostatic bowl vent valves connected to the external bowl vents on a Motorcraft 4180 carburetor, also with air cleaner bowl vents:





I will refer you to the above abstract from the patent:

The normal objective in a vent valve of this type is to allow during engine hot soak conditions the flow of fuel vapors from the carburetor fuel bowl into the carbon canister to be adsorbed therein for storage during engine shutdown.


I never claimed to be an engineer, so I don't really know how this will happen. But that is how it works. I suppose the fuel vapors will follow the path of least resistance. And since the charcoal canister is colder, the vapor pressure is lower, and presents much less resistance?


Again, I will refer you to the above abstract from the patent:

The well contains a vacuum operated vent valve that is spring opened during engine-off operation to allow the storage of fuel vapors under engine hot soak conditions.


When the engine is hot and shut off, the fuel from the carburetor fuel bowl evaporates more than usual, producing excess fuel vapors and emissions. The thermostatic vacuum bowl vent valve will be OPEN, providing a clear, open path from the external bowl vent, through the hose, and down to the charcoal canister, where these excessive vapors caused by hot soak conditions will collect in the charcoal canister.

Because the valve is thermostatic, it will close off when the engine cools down again and there is less evaporation, which prevents the stored vapors in the charcoal canister from gong back through to the carburetor fuel bowl (and ultimately through the air cleaner vents and into the atmosphere). *Some* evaporation will still occur in the fuel bowl, and those vapors will evaporate through the air cleaner vents and back into the air cleaner, which helps for the next time the engine is started cold. (But if the engine is OFF and the temperatures get high enough under the hood, the thermostatic valve will open again, to once again allow excessive fuel evaporation from the fuel bowl to vent to the charcoal canister.)

When the engine is started again, the thermostatic bowl vent valve will CLOSE - no matter the temperature - and the stored fumes in the charcoal canister from the fuel bowl and the gas tank will be sucked into the PCV valve (or PCV hose) by the canister purge valve via a ported vacuum switch to be burned in the engine.


SUMMARY:

I. - Engine on
All conditions = Valve CLOSED (manifold vacuum)
This will successfully "cap off" the bowl vents. The carburetor fuel bowl will only vent through the air cleaner vents.

There is a good reason for this. The canister purge valve uses ported vacuum to turn on and off, but uses manifold vacuum to purge the charcoal canister. When the canister purge valve is "on," the vacuum would suck fuel out of the fuel bowl if the fuel bowl was allowed to vent to the charcoal canister when the engine is running.

Another good reason is something you said in your last post:

RIGHT?


II. - Engine off
A) Cool conditions = valve CLOSED (thermostatic)
The carburetor fuel bowl is closed to the charcoal canister and will vent minimal fuel vapors through the air cleaner vents and into the air cleaner.

There is a good reason for this: the richer mixture helps with cold starts.

B) Hot conditions = valve OPEN (thermostatic)
The carburetor fuel bowl vent will vent excessive fuel vapors generated from "hot soak" away from the air cleaner and into the charcoal canister.

There is a good reason for this: 1. - the richer mixture will cause hard hot starts, and 2. - Emissions regulations!

That is why Ford called this the Evaporative Emissions system.



If anything I wrote above is "ridiculous" to you and "defies the laws of physics," then we are both missing something in this equation. Because this how it is explained in every single publication I have read on the subject, and it also goes along with the explanation of the function of the thermostatic vacuum bowl vent valve from the patent.