Ricko1966
Full Access Member
- Joined
- Apr 11, 2017
- Posts
- 5,011
- Reaction score
- 7,758
- Location
- kansas
- First Name
- Rick
- Truck Year
- 1975
- Truck Model
- c20
- Engine Size
- 350
The vent line allows the tank to breathe, in and out. Without releasing evaporated fuel,or drawing in moisture like you would with a vented cap. The evap system let's you burn more of the gas you bought,helps prevent contamination of your fuel,rusting out of your tank, and my own personal theory is the lighter molecules of the fuel evaporate more than the heavier leaving you with a potluck soup of fuel. Not after 1 tank,nut after 1000?@legozombie Have you been able to test out Ricko1966's tests? I'm currently in the process of installing the fuel system on my 1976 K20 and am curious what you find. I spent most of last week trying to understand how the evap system works. I fully agree it sounds like a vent problem.
What I'm not 100% clear on is the evap system is for capturing fuel vapor from the tank. When the fuel is being consumed while driving, a vacuum is generated and air needs to be able to flow into the tank to equalize the pressure. I'm not clear how the evap system would allow this. If it doesn't then a vented cap is necessary. Or, perhaps the vent line that goes to the air cleaner allows a backflow of air into the tank. (?)