Charcoal canister, help me understand.

[dmopar74]

73 duster 225, one line runs to carb vent, Holley 1920, one to tank vent, and the purge line is capped off. Where is the purge line supposed to go? Manifold vacuum? Teed into the ported manifold line running to the distributor? The factory emissions controls has been deleted by me but I bought the car with the canister purge capped off. Not sure if this is related but after I shut the car off the fuel drains back into the tank almost immediately, makes starting the car a real treat.

 

[AJ/FormS]

Not sure if this is related but after I shut the car off the fuel drains back into the tank almost immediately, makes starting the car a real treat.

It is physically IMPOSSIBLE for the fuel in the bowl to run back to the tank.
If your bowl is going empty, the fuel is going someplace else, and these are your choices;
1) it's evaporating
2) The lightest elements are boiling off, leaving syrup that is too heavy to light off
3) the bowl has a hole
4) or a bad gasket, or
5) the bowl vent is closed.

The bowl vent should be routed to the canister. If the canister is sealed, the bowl cannot vent. If the bowl cannot vent, then the atmosphere cannot push fuel up the wells and that's it you got a no start.

The purge valve is sometimes operated by venturi vacuum, and sometimes by manifold vacuum. But if by manifold vacuum, it should have controls on it, so that it cannot operate at idle, nor on a cold engine.
There should be a hose map on the underside of your hood, detailing the hook-ups and the routing.
If your system was venturi-vacuum, there should be a small metal pipe (~1/8 inch od by maybe a half inch long) passing thru the side of the venturi, on the passenger side. This system varies the purge in proportion to how far the throttle is opened.
On the underside of the canister, there should be a fiberglass filter. They get plugged up with road dust over time. They say the charcoal may get clogged or lose it's ability to attract and hold gasoline vapors. IDK anything bout that.

 

[dmopar74]

It's not letting the bowl, it's emptying the fuel line, sorry bout that. As you can see the purge line is capped off.

 

[72bluNblu]

Let's try this a different way.

How do you know it's leaving the fuel line? And, is it just leaving the fuel line between the carb and the fuel pump? Or is the entire line from the carb to the tank going dry?

 

[dmopar74]

Let's try this a different way.

How do you know it's leaving the fuel line? And, is it just leaving the fuel line between the carb and the fuel pump? Or is the entire line from the carb to the tank going dry?

I have a clear filter before the carb, and the gas siphons back once the car is turned off. It will run off the bowl, then stall. Usually have to crank for a while, id say up to 20 seconds before getting fuel back to the carb. Not sure if the capped purge on the canister is causing this or a tired fuel pump.

 

[72bluNblu]

I have a clear filter before the carb, and the gas siphons back once the car is turned off. It will run off the bowl, then stall. Usually have to crank for a while, id say up to 20 seconds before getting fuel back to the carb. Not sure if the capped purge on the canister is causing this or a tired fuel pump.

Does the oil in your engine smell like fuel?

Not a /6 expert, but I believe the only way the fuel should be able to leave that section of fuel line the way you describe it is through the fuel pump diaphragm and into the crankcase. Assuming there's no outside leak in the line.

 

[slantsixdan]

Purge line is meant to go to the carburetor's purge port, or teed into the PCV hose via a purge valve as described in this. You should fix it properly, but it's not causing your hard starting.

 

[dmopar74]

Does the oil in your engine smell like fuel?

Not a /6 expert, but I believe the only way the fuel should be able to leave that section of fuel line the way you describe it is through the fuel pump diaphragm and into the crankcase. Assuming there's no outside leak in the line.

I'll check that out

 

[AJ/FormS]

It's uphill from the fuel pump to the tank, ...... It's not gonna syphon unless air gets in between from the pump end, and only if the jumper at the back is good and only if the tank is under suction. That's a lot of ifs.

I got some possibilities for ya.
1) make sure the tank is vented
2) Open the gascap, remove the jumper at the pump, then make sure you can blow thru the hardline with compressed air, and hear the bubbles in the gas.. Those small lines tend to collect moisture in the lowest parts and rust there, sometimes completely blocking the line.
3) check the jumper at the tank, from the hard line to the sender. My guess is that, if items i and 2 above turn out OK, then, at idle, the pump is sucking air at the jumper and filling the hardline with air. As the rpm goes up, the pump begins to get fuel, enough to drive around on, at normal rpms, but it is always getting some air. When you shut it off; all the fuel in the line between the pump and tank, collects in the lowest place, and all the fuel in the line between the pump and carb, collects at the pump, assuming the pump check valves are holding. So then, when you go to start it, the pump cannot pump anything until it gets rid of the air in the line and pulls up the bit of gas that is in the low spot. Then it can use that as a primer and push up whatever is in the line to the carb. If yur lucky, that is enough to start up on, and if you rev it up, maybe the pump pulls enough from the tank to get going again. But if you don't rev it, it runs out and stalls.
Change the jumper and if using gearclamps, install 2 per side, with screws offset 180*.
While yur doing that, replace the jumper at the front also, cuz chances are they both the same age.
4) Yank the pump off and check the return spring tension.
While yur there, chuck the pump into a vise, and see if it will pull on the suction side.

 

[RustyRatRod]

It appears you have the vast majority of the vapor return system intact. I would get it operational. It can actually increase MPG a little bit.

 

[Dana67Dart]

Not sure if this is related but after I shut the car off the fuel drains back into the tank almost immediately, makes starting the car a real treat

The fuel in the carb can not drain back into the tank

The float needle seat is at or above the level of fuel in the bowls and can't syphon once the level is below it.

I suspect you have some other issue as A/J noted.

You can test all this out.

Next time you suspect fuel has drained back. Pull the air cleaner and pump the carb, look down the bore for fuel from the accelerator pump.



You might be having some fuel quality issues as well. Alcohol blend fuels are problematic in our cars.

I had a problem when the engine was HOT, accelerating from a light it would start to die then letup on the gas, and it would recover. Then ease back on the gas and it's all good.

I switched to alcohol free gas and I can't make it happen any more!

NO OTHER CHANGES!

Pure-gas.org - ethanol-free gasoline in the U.S. and Canada

 

[H22A4]

Pure-gas.org - ethanol-free gasoline in the U.S. and Canada

That website might be accurate for the States but in Canada the federal Government passed legislation requiring ethanol in every grade of gas (minimum content of 5%) since summer 2023.

 

[Dana67Dart]

That website might be accurate for the States but in Canada the federal Government passed legislation requiring ethanol in every grade of gas (minimum content of 5%) since summer 2023

I'm so sorry for your loss.