Vapor return setup with 1970 "Evap Control System"?

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MopaR&D

MopaR&D

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I got a fuel filter with a vapor return fitting (intentionally, would like to reduce fuel boiling) and did some searching around here about how to make it work, my car does have a return line to the tank which is kind-of a vent as I have the briefly-used (pre-charcoal canister) ECS emissions control on my sold-in-California 1970 Duster. Should I add another vent somewhere based on the diagram below? This is straight from my 1970 Plymouth FSM...

Evap system capture_FSM.JPG


The "Vapor Liquid Separator" is a near-vertical tube in the trunk fairly close to the filler tube...
 
The return line from the filter is designed to have fuel in it, not fuel vapor. So going back to the vapor-liquid separator via the vapor line may cause issues, in that you have eliminated the tank vent.... unless you switch to a vented cap.
Perhaps run a line back and pirate 1 of 4 the liquid return lines to get into the tank. Block it going up into the separator. IIRC, they switched to just 1 liquid return line in subsequent years, so pirating 1 out of the 4 seems like it would be OK.
 
nm9stheham said:
The return line from the filter is designed to have fuel in it, not fuel vapor. So going back to the vapor-liquid separator via the vapor line may cause issues, in that you have eliminated the tank vent.... unless you switch to a vented cap.
Perhaps run a line back and pirate 1 of 4 the liquid return lines to get into the tank. Block it going up into the separator. IIRC, they switched to just 1 liquid return line in subsequent years, so pirating 1 out of the 4 seems like it would be OK.
Click to expand...

I have a parts-store cap so I think it's vented but I'd rather not have that be the only vent source. I'm sure I could get away with using one of the ports you mentioned. Sounds like I need to fab another line from the tank up to the engine bay?
 
Yes, that is what I am thinking.... extra line for the fuel return. Leave the vent line as a vent line to the front. IIRC, that '70 was designed to vent the gas tank fumes into the crankcase so that present line to the front IS the vent line.

And be careful on some of the parts store caps.... not all of them are vented even though they have what looks like a vent mechanism.
 
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