Quote:
Originally Posted by Shiny
Just trying to learn by following, but I'm not understanding how venting a tank will cause starting issues.
The pump pumps with or without a vented tank, doesn't it?
If the tank has no vent, the pump suction will build vacuum, which OP describes, but the pump still delivered gas to the engine. OP says it ran well without a vent.
I can imagine the pump dropping flow without the tank vented, but it obviously was still moving gas when the tank was not vented. Doesn't this suggest the tank is getting some air to replace the gas pumped? Maybe the cap has a vent that will hold some vacuum, but still let air into the tank when the vacuum builds?
Is it possible the fuel pressure at the engine increases when the tank is vented? If so, how would this cause starting issues?
I am also confused by "I'm running... with no vapor line", then later "It doesn't stall when the vapor line is capped".
Might be helpful to get more details?
For example, mechanical pump? Carb or FI? Does the pump have a vapor return that is blocked, then opened? If original tank, how is it now sealed? What cap is on the tank? Are you sure it isn't allowing air into the tank?
Sorry, but I'm not following all this but it's interesting!
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For a fuel system to flow fuel a couple of things need to happen:
1) Atmospheric Pressure and a flow path to a lower pressure area or a different altitude for the fuel source.
Example. Some of the old Ford Model Ts and Model As did not use a engine driven fuel pump. They used a Gravity Feed System. (The fuel tank was mounted higher vs the card on the engine). A friend had a fuel line fail at midnight on the afternoon shift and he had a 40 mile drive back to his home.
So we disconnected the inlet side of the fuel pump on his vehicle, plugged the fuel line from the fuel tank, ran a line from a 5 gallon fuel can (mounted & taped down on the roof of his car), and he started the car and drove home at 20 mph on back roads to his house.
He had a shop fix his leaking fuel line and he was able to borrow a vehicle for a day to make it to work.
But our "jerry rig" fuel system still required that we leave the fuel cap loose so that atmospheric pressure could allow the fuel to flow from the fuel can to the fuel pump inlet.
Been there done that. And yes the Tanks Inc tank vent is not a good one.
Trapped air in the tank still allows some fuel to be pulled from the tank.
Tom V.