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1974 620 Weber DGV & Fuel Evap Line


jkelm24

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On 7/1/2020 at 1:04 PM, AlexDeLarge said:

Yes Mike, I am keeping the pcv valve. Correct me if I am wrong, but from what you are saying, I can block off both ports coming from the flow valve and run a vented gas cap? I was thinking I had to keep the bottom line to the crankcase and just cap the top line which returns through the air cleaner. Screenshot_20200701-155238.thumb.png.be18b418dbb7e2ca10670c6d31155fd2.png

 

 

 When the engine is off, evaporated gas fumes (under very slight pressure) pushes through the flow guide valve and into the crankcase for storage.

 

When the engine is started these fumes are drawn into the intake by manifold vacuum through the PCV valve and burned.

 

As the tank empties of gas (a very slight vacuum) pulls the flow guide valve open allowing air from the air filter back into the tank to replace it.

 

 

Now I could be wrong but I think a vented gas cap only lets air in to prevent the tank imploding as the gas is emptied. This is fine for replacing the gas as it is used up but if you block all the flow guide valve hoses and the car sits out in the sun on a hot day the fumes can't get into the crankcase. I'm not sure how much pressure would be produced from this but if if over 5 PSI it could over power the float and needle valve in the carburetor and flood it. To put it into perspective 5 PSI is about 1/3 of the pressure inside a party balloon. It's not much. As I said, I don't know what would happen for sure, just something to be aware of.

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On 7/1/2020 at 1:11 PM, AlexDeLarge said:

On a side note Mike, since I have had the truck the lines on the stock air cleaner were never hooked up. When I removed the stock carb, that return line to the flow valve was "T'd" with one line going to a port on the EGR manifold and one going to a port on the BCCD. Never could find any diagrams of that in the FSM. Thanks for your help....attached a picture, just disregard my labeling.562139851_20200624_154027(2).thumb.jpg.d57709ca331aa9ff0bb13871a97b389a.jpg

 

 

Maybe connected up wrong. There should not be any vacuum on any of the flow guide valve hoses.

 

All L20Bs with ATC (Automatic Temperature Control) have a small vacuum line to the air filter to work the vacuum motor in the snorkel. The hose to the flow guide is just for filtered air going back to the gas tank.

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4 minutes ago, datzenmike said:

 

 

Maybe connected up wrong. There should not be any vacuum on any of the flow guide valve hoses.

 

All L20Bs with ATC (Automatic Temperature Control) have a small vacuum line to the air filter to work the vacuum motor in the snorkel. The hose to the flow guide is just for filtered air going back to the gas tank.

I appreciate the explanation of the evap system, I understand how it works now. I had a hunch those lines were hooked up wrong. I am just trying to figure out how to hook these lines up using the Weber. In theory, would it work if I added a small breather to the valve cover outlet and ran a vacuum hose from the return side of the flow valve to the 90 degree fitting on the Weber air filter? Also in the future, if I was to get a weber adapter for the stock air filter maybe run the return from it? 

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On 2/27/2019 at 7:11 AM, FrankRizzo said:

Where would I get one? I was hoping that someone makes a clean looking canister, but I cant locate one

You should be able to find something suitable at the local wreckers - they essentially all function the same. To clean up the engine bay consider making a box that covers it - the box could also mount up other under hood bits so would serve more purpose.

 

One other issue with simply deleting the evap can and just putting on a vented gas cap is the potential for vapor lock on a hot day - gas fumes gotta go somewhere or they go nowhere.

So DO connect an evap can and DO connect your PCV. Just sayin' 🙂

 

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12 hours ago, AlexDeLarge said:

I appreciate the explanation of the evap system, I understand how it works now. I had a hunch those lines were hooked up wrong. I am just trying to figure out how to hook these lines up using the Weber. In theory, would it work if I added a small breather to the valve cover outlet and ran a vacuum hose from the return side of the flow valve to the 90 degree fitting on the Weber air filter? Also in the future, if I was to get a weber adapter for the stock air filter maybe run the return from it? 

 

I would avoid the little breather on the valve cover vent. (it's really a fashion accessory by those that don't know better)  Under certain conditions fumes push back through the filter so best it's connected to the air filter and they are sucked into the engine and burned rather than breathing them or the filter wet with oil. The hose to the air filter is only for clean air to go into the gas tank as it empties. You could drill a small hole in the air filter base and poke the hose inside or put a smaller filter on the end of the hose. Myself, I doubt much dust gets into the gas tank anyways.

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