Holley 1920 Bowl Vent

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1970Dart198

1970Dart198

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I have Holley 1920 carb # 6156. My bowl vent is not hooked up to anything, I believe it went with the ECS system. I was wondering if I should plug the bowl vent? What exactly does the bowl vent do?

I had the old crankcase inlet air-cleaner, and I saw that two hoses come out of it, one went to my air cleaner, while the other went to a small hose to the back of the car.

Where can I get a "new" crankcase inlet air cleaner, that can take both hoses? I have that aftermarket one on right now that just has the fitting to the air cleaner.

Thanks!
 
The bowl vent goes to the bowl vent port on the charcoal canister. If you don't have one of those you should plug the port on the carburetor or get a canister. The canister would take the fuel vapors vented from the gas tank and feed them back into the carburetor.

I can't help with the air cleaner. I don't know that I've seen one with two ports on it.
 
IIRC, the vapors from the float bowl as well as tank vapors were routed and stored in the canister. Then,during purge mode,those vapors from the canister were drawn up to the carb and entered just above the throttle blades. On some cars there was a vacuum line to a purge valve, which the factory manipulated in different ways to achieve smoother running.
In any case if your system is incomplete, just remember the bowl has to be vented to atmosphere somehow, or else the engine cannot run. The carb depends on the atmospheric pressure to push fuel through the various circuits.
Waitaminute.
There was a time when they used the crankcase as the vapor storage tank. Vapors from the tank and the bowl were collected in the crankcase and then routed back to the carb after start-up.I think that was a continuous purge system, with a breather on the valve cover that was kinda funky looking with 2 and sometimes 3 hoses coming off it. I forget how it all worked.
 
Can I just run a hose from my fuel bowl vent to the Tank Vent Line that I currently have plugged up? I don't like the smell of gas after I shut the engine off, knowing that valuable fuel is evaporating from the bowl vent. I would much rather have it vent back to the fuel tank via the Tank Vent Line. Will that work? I don't really have anywhere to put the Charcoal canister, and new ones cost around $125! And that's IF they are around! Thanks.
 
If you are smelling the gas, You must have a keen nose, or something else may be going on.Or its very hot outside. I would check the fuel system over very carefully for leaks or evidence of leakage or seepage.Or perhaps the fuel is percolating after shut off. Or the fuel is puddling on the intake floor.I mean the normal rate of fuel evaporation is generally so slow, on a properly functioning, even non emission vehicle, that most people dont notice it, unless the vehicle is parked in an enclosed space.
-You could vent the carb to the tank, but if the car has a non-vented filler-cap and the float bowl is not otherwise seeing atmosphere,then it will not give you the result that youre after.The engine will not run very long. And if the filler-cap is vented, it will still stink up the garage.The tank also has to see atmosphere.If it does not see atmosphere the fuel pump will only pull fuel out a short time before the tank will begin to collapse and the engine may/will quit.
-If your fuel system is not leaking or seeping and is otherwise correctly working, and you find the smell objectionable,the best solution is to restore the vapor storage system.
Its imperative that the float bowl see atmosphere when the engine is running. And the tank must see atmosphere at all times,or else it will balloon in the hot sun, or collapse when the engine is running.
-So,The tank can be vented to the crankcase. That solves its requirements. And the bowl can also be vented to the crankcase when the engine is off.The crankcase must be almost sealed when not running( that is to say no leaking gaskets or seals or dip-stick), but it must be open to atmosphere when the engine is running.That solves the carb bowl requirements. The PCV system will pick up the vapors after start-up.But the float bowl must NOT see the PCV after start-up. That would wreak havoc with the calibrated fuel circuits.
-I have seen carbs on cars from that period, that had a bowl vent-valve operated by the throttle linkage. When you stepped on the gas-pedal the linkage would lift a little poppet valve on top of the fuel bowl and voila, bowl vented. Foot off the gas, bowl vent closed. Perhaps your carb has one of those and its not set right. If the idle speed screw has been turned up too far( and there are reasons for that) then the linkage might need to be reset.
-A used canister should work fine.Unless its been polluted or run a bazillion miles. They last a really long time.
-These venting systems may not be rocket science, but it all aint that simple either.
-I had a 70 Swinger 340. It did not have the canister. I had a 71 Demon, and a 71 Monaco. I cant remember seeing one on either of those.
-What are you working on?
 
I park my car outside. After I drive around a bit and turn off the car to do a few errands, I smell a hint of gasoline. When I come back 20 minutes later to restart the car, I have to crank it over and punch the gas to fire up the engine. I did the fuel line mod, and my thermostat is at 180 degrees. I had the carb rebuilt, I set the valves properly, new thicker carb base gasket and adjusted throttle and kickdown. New PCV valve and grommet as well. The only open port on my carb is the fuel bowl vent. I had the old breather cap that was connected to the air filter and the fuel tank vent line that begins at the firewall, but it was filled with so much sludge. I replaced it with a new breather cap just to the air filter housing.
 
If you still have the old breather, they can be cleaned out by soaking in solvent, paint thinner or in a pinch, gasoline.Let soak for a day or two.Then follow with a water rinse and blow out with compressed air.Protect your eyes. If using gas, be very,very careful to not set stuff on fire.
-The problematic hot-start situation,speaks to a fuel percolation problem.If the engine is allowed to cool several hours after the roadtrip, is there still a starting issue? eg; long cranking time. What about after a couple of days.Still long cranking times? What about 5 minutes after hot shut-down? Each of these situations has its own solutions.
-What fuel are you using? Oxyginated? Octane? Summer/ winter blend?
-Is that on a slanty;where the two manifolds are stacked and bolted to eachother? Do you have a functioning Heatriser Valve? Or EGR system? Do you have a heated air intake system? Is the air cleaner housing original? Is there a pipe from air filter housing to exhaust heat stove? Are the ignition timing systems all functioning correctly?On which side of the fuel pump is the filter located and is it returning fuel to the tank? The vent line that ends at the firewall, is it open to the tank and not obstructed? Is the filler-cap vented or not?Is the carb throttle plate(s) open too far,possibly due to late ignition timing, loss of compression, cool running, other mechanical or tuning problems or just plain personal preference?
-I believe the major source of the smell is the tuning issue, and probably not the vent system at all.
-Heres an experiment for you. Take a 1/2 quart glass mason jar.Fill it up about half way, with FRESH, from the pump, fuel that you are normally buying.Set it on a level surface and carefully mark the fuel level.Do not seal the jar but just cover it with something not combustible,and leaving a tiny breather hole, maybe 1/16 to 3/32inch dia. Go set it outside in a safe place(a metal pan; not pail), and not in the sun.Recheck the fuel level after 20 minutes, 1 hour, 6 hours, 24 hours and once a day for a week. Mark and label each interval on the outside of the jar.Now you will be able to see the normal rate of evaporation, and see where Im coming from.
-I see a bunch of questions above, and they will all need to be addressed in order for us to try and solve your aroma issues.
BTW, if you remove the air filter housing, you can look down into the carb. You should find a bowl vent in there. Look very carefully. You might not recognize it at first.So even if you plug the one you can see.......
-What fuel line mod are you talking about?
-TTYL
 
The air cleaner is original, I do not have the thermostatic air cleaner hooked up because it creates a vacuum leak. The thermo sensor makes a vacuum leak and does not pull the door open on cold starts.

My heat riser works, as well as my choke, i'm fine tuning the automatic choke to open at certain heat levels. I use 93 octane gas. I would like to install a fuel/water separator, and I am in the market for one. I believe the new gas these days evaporates so quickly that it boils easily in a carb. My slant six is pretty healthy it terms of Ignition, I installed a Pertronix ignitor kit with a 3 ohm coil to supplement the hotter ignition. I have a new cap, the famous CH-410X, and new spark plug wires as well as the NGK ZFR5N plugs with the washers removed to obtain a hotter spark. I timed the engine perfectly. New SMP fuel pump helped a lot with filling the fuel bowl before firing up the engine.

See the gold breather cap and the plugged line below the blower motor? The line runs to my fuel tank.
 

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As said, connecting the bowl vent to the tank vent will not work; both will try to be sucking air from the other as the gas is consumed and the car will stall or the tank will be sucked in. You could tie them together but you would have to include a tee and route the vent somewhere so that gas vapors would not be going anywhere bad or where it could suck in dirt or moisture. That is the nice part of the charcoal cannister; it is the 'tee' and safe vent. (The tank in particular has to vent in and out a lot).

As for the bowl going empty, I would remove the air cleaner and look hard down the throat of the carb after hot shutoff, and see if any fuel is dripping down the carb. Do this multipel times. If you see any fuel drip in the throat, you have a carb leak, and an immediate rebuild is in order. (Any such fuel drip can/will get into cylinders each time you stop and wash off the oil and cause severe bore wear.) This would cause the fuel smell too.
 
SMP fuel pump? Is that electric? Is it regulated down for carbs; say to to 4 or 5 psi?
When you plugged the tank line at the firewall,did you install a vented filler-cap? If the tank is not vented, it will collapse. How many times has that been said by now?And it would not be wise to vent the tank through the line to the firewall by the heater blower motor or near ignition system parts. That would be a fire waiting to happen.
-So far as I remember, Chrysler vacuum thermo valves always suck a bit of air.Thats how they work. It is sampling the air temp. and actuating the stove door. Its designed to maintain a certain inlet air temp to the carb.IIRC it was 80*F. The carb was factory calibrated for that air leak, and to operate at that temperature.If you defeat that system or it is not operating correctly, you will have to recalibrate the carb to compensate; especially if you intend to drive it at colder temperatures, such as wintertime. You may also experience carburetor icing.
-If you dont have the tools or skills to do that, then I urge you to restore the systems to stock.You only have to experience icing in traffic once to scare the **** out of you.
And dont be belly-aching about the money.Poor people dont have cars at all, never mind a nice classic like yours appears to be. And if you cant find the parts used, I venture to say that youre not looking hard enough.
-You will spend more time and money engineering work-arounds and band aids, then if you just restore it to the way Chrysler engineered it.Those guys knew their stuff.
-If you intend to continue down this path, I think most or all the info you need can be found in this thread.I gotta go now.
 
There's a simple explanation here that you may not view as simple:D, although by now it sure has been overcomplicated.

Your car uses the early version of the vapor recovery system before they began using charcoal canisters.

1. There is no charcoal canister, never was. You can add one if you wish as long as you plumb it according to the '72 and later diagram.

2. The 2-port PCV inlet filter is rare. Only used two years and people on here that sell them get big bucks...so don't throw it away. In addition, as has been stated more than once, that filter is EASILY cleaned with some solvent, such as gas, then a re-oiling.All there is inside it is just metal mesh. Just clean it.
Whomever convinced people to pay for a new one back in the day was right up there with whomever convinced people to start smoking cigarettes.

3. The way this system works is, the bowl vent on the carb is supposed to connect to a port located on the top of the fuel pump housing. The idea was that the vapors would travel down the line and be drawn into the crankcase, then recirculated through the PCV system and burned.

The line that is there at the back of the engine near the firewall is the vapor line from the fuel tank. It's intent is again to capture fuel vapor from the tank, and draw it into the engine to be eliminated.

If you go back and take a look at the tank you'll probably discover the "4-corner" vapor recovery system on the tank, which is simply a system that drew the vapors from each upper corner of the tank.

Lastly, in the trunk you should see a standpipe next to the actual filler tube for the tank. That standpipe is a vapor separator to prevent any possibility of liquid fuel being drawn up into the vent line leading forward to the engine.

4. At this point you have pretty much totally disabled the system due to not understanding how it worked. That's ok, because I've explained to you exactly how the system works. Don't go randomly plugging lines off. When you capped off the vent line at the firewall, you prevented the tank from being able to vent properly.

If you cap off the carb bowl vent, the vapors will build up and the engine will spin and spin and spin on every hot start. Been there.

As I said, you can either convert it to a charcoal canister arrangement, or put it back like it was intended to be.

The only caveat is that you may no longer have a fuel pump with the proper nipple on top, although it can be added. Hopefully someone was curious enough to wonder why there was a loose line hanging around, but most people aren't.

This system was used through 1971, then '72 started the canister. California cars may or may not have switched between the two at different dates.
 
AJ/FormS said:
Big bucks, eh?....I might have some of those somewhere in my stash.
Click to expand...

Well I tried to buy one through the classifieds once and when I heard "what's it worth to you"...no.

Big bucks relatively speaking for what a filter is worth:D
 
Would it be wise to drive around with the vapor line from the fuel tank open? I have a new locking gas cap that is not a pressure release type. My fuel pump is the mechanical, non California emissions style made for carburetors. There is no hose connector on the fuel pump. I have a new fuel tank, and it does have the 4 hose connections on the side of it. I do have the separate tube that runs up the left side of my trunk. I have the old 2 port PCV filter, and I cleaned it once with kerosene, but it didn't help that much.

I'm in college, and my old 2 port filter is at home in Connecticut. Is there any way to retrofit/ undo so that my tank vents properly and I don't lose valuable fuel vapors? Until I can return home and clean and re-install the old type crankcase element?

Thanks!
 
I have had a few beater cars over the years with this same carb and they just used a piece of hose and stuck a bolt in it and it ran fine that way fine.
 
Ok, so what I will do is un-plug the fuel tank vent line, leave it open until I get to CT next week. I'll clean up the old 2 nipple valve cover breather and hook it all back up.

I can buy a fuel pump with the nipple on it and hook it up to my carb bowl vent to make everything complete.

My car runs and drives fine, its just the fact that there is a gas odor when I shut the car off that irritates me because I know I'm losing valuable fuel.

Thanks!
 
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