Help on fixing a vapor lock!!!

[Mattax]

It’s a 73 swinger with mopar electronic ignition. Holley 1bbl

Read what Chrysler was telling their techs about vapor lock and fueling problems.
Some vapor in the top of the fuel filter is normal, but should not fill the whole thing!
Tilt the filter up so it bups out like Chrysler started doing in '63
Carburetion and Performance Diagnosis (Session 188) from the Master Technician's Service Conference

Changes in fuel, the need to run hotter idle temps, and the vapor controls sometimes called for additional measures.
Some car/engine combos got a special fuel pump with a small internal bypass.
Techs in '72 were reminded they could use the external bypass kit for cars without the special pump that had hot start flooding.
1972 Imperial & Chrysler Engine Performance Facts & Fixes Service Book (Session 291)

For 1973 specific info, scroll down
Master Technician Service Conference - Chrysler's Training for Mechanics
there are 3 sessions that may be helpful to you
Cleaner Air System Highlights
Getting them Started
Exhaust Emissions and Drivability.

I removed the fuel pump to carburetor line and covered it with 3/8" rubber hose split and put over it and fastened with zip ties. It made a difference with my truck. Rubber hose is a good insulator.

That's smart thinking.

Long runs of rubber hose are never good.

And I’ll have to watch the choke on the car as idles.

Automatic chokes have three parts of operation.
Full choke when you set it by moving the throttle before starting.
Qualified when the flap opens slightly with engine starting. Vacuum from engine is used to open it to this position.
Opening as the bi-metal coil heats up,. In '73 assisted by an electric heater when temperatures are above 60 F.

As far as the 'new and improved' flat needle and seat, that's some SSS.
Daytona's 'improved' Inlet Needle & Seat?
(just click the x if your asked to join tapatalk)

 

[RustyRatRod]

That's smart thinking. Long runs of rubber hose are never good.

I never have liked it either.......but I'd actually endorse the EFI hose Dan talked about in his fuel line mod.......I just don't endorse the "look" of it. I know, that's a stupid reason, but it's my reason. lol

 

[72Dinger]

I agree 100% about the return filter. They are a great idea. Anything you can do to reduce the fuel temperature helps and keeping it recirculating certainly helps that. Says the professional typist.

Return filter before the pump, or in between the pump and carb? Or does it make a difference?

 

[RustyRatRod]

Return filter before the pump, or in between the pump and carb? Or does it make a difference?

I like the return junction as close to the carburetor as possible, so after the pump just like the factory did it.

 

[Mattax]

I like the return junction as close to the carburetor as possible, so after the pump just like the factory did it.

Agree, otherwise it would suck.

 

[72Dinger]

Agree, otherwise it would suck. View attachment 1715401708

Thats what I was thinking. Read the following on an AMC thread available here:
Carb boil over
(reply was in response to adding a return filter - my emphasis added)

Where this will help is in vapor locks. This is where the fuel in the line before the pump is boiling.
This happens because fuel does not move if the carb is not calling for it. Also any liquid on the suction side will boil easier than when under pressure, why you don't here of FI cars having vapor lock as the line from tank to motor is under pressure. Look at a cooling system it uses a pressure cap as this will raise the boiling point of the coolant, IIRC 1 psi = 2 deg.
Because the pump can only pulp liquid and not vapor it locks the fuel from moving.

Any thoughts?

 

[Tooljunkie]

Something i read about the clothes pin thing. Was to let them soak in water. Not sure where i read it, im thinking old popular mechanics encyclopedia

 

[Mattax]

Thats what I was thinking. Read the following on an AMC thread available here:
Carb boil over
(reply was in response to adding a return filter - my emphasis added)


Any thoughts?

First. When I wrote it would suck, that was a pun!
Basic vapor return set ups look something like this.

So you can see what will happen if the return is joined to the feed line before the pump.

"liquid on the suction side will boil easier than when under pressure,"

Yes. This is also correct. True for any liquid. As is the reverse. Practical example is automotive coolant systems. They run under pressure so boiling point is moved up above 212 even if running straight water.

That said, vapor lock can occur on the pressure side if there is enough heat at or after the pump and routing prevents the vapor from escaping easily.
Flooding occurs when the vapor does escape, but pushes a bunch of liquid fuel in front of it.

 

[Mattax]

The comments in that thread about the fuel are basically correct.
What we call gasoline is mixture of components - some of which is refined petroleum.
It vaporizes over a wide range of temperature depending on the mixture.
All that needs to happen is enough of the lighter components to vaporize and build enough pressure in a bubble to block the flow of fuel.
In this case regulation may be in our favor since it caps the RVP allowed. Higher RVP means more likely to vapor lock.
Running winter fuel on a hot day is when I've had the most troubles with vaporization both at the carb, and in a few cases vapor lock where hardly any fuel was making it to the bowl.
Gasoline Reid Vapor Pressure | US EPA.
Reid vapor pressure - Wikipedia

 

[Mattax]

This gives some idea of the temperatures pump fuels evaporate over.
From a published test with the distillation points I plotted a non-reformulated gasoline from 2007, and one from that time with 8% ethanol.

Read the graph like this:
Find a temperature on the left. Take 150* F. Follow the line across to the Chevron Premium, and then go straight down to the bottom axis. For 150*F, we see about 7% of this fuel evaporated. While the same 150* F caused 30% of the other fuel to evaporate. Big Difference!
Neither of them fully boil off until over 400*F.

Also notice the shape of the E8. This is a problem with a lot of the RFG pump fuels. The light portion vaporizes easily, but then there is a jump to the mid range and completion. This disrupts the flame front in a relative cold cylinder.

 

[72Dinger]

Agree, otherwise it would suck.

I got the pun! Thanks for the solid info. Piecing it all together, having the return filter behind the pump won't actually do much of anything since fuel under most conditions won't be heated enough (even under a mild suction) to cause much in the way of evaporation, at least not nearly as much as fuel after the pump (at 5-7 psi), picking up heat from the pump mechanism and absorbing heat from the engine.

I'm looking to install the return filter because my charcoal can is long gone and I have the return line wide open and gas fumes are stinking up my garage. My existing fuel filter is on the suction side of the pump. At some point soon I'm going to replumb my fuel lines.

I did notice yesterday that the stock 1/4" hard return line appears to have an orifice in it already where it would connect to the charcoal canister. The hard line steps up to a larger OD to accept 5/16" ID tubing, but appears to have a much smaller ID/orifice. I didn't measure but it looks awfully close to the orifice size I see when I peer down the fuel filter.

 

[Mattax]

I did notice yesterday that the stock 1/4" hard return line appears to have an orifice in it already where it would connect to the charcoal canister. The hard line steps up to a larger OD to accept 5/16" ID tubing, but appears to have a much smaller ID/orifice. I didn't measure but it looks awfully close to the orifice size I see when I peer down the fuel filter.

That's interesting.
A small diameter orifice seems typical in vapor seperators.
But maybe not in return style filters?
Lemme look at one I cut open - even though its AMC wagoneer with charcoal canister.
Yup. Look at that. It's got a reduced opening as well, just not as tiny as in the seperator. (These are always installed with return at 12 o'clock position.)

Makes sense to restrict fuel from returning to the tank but would easily allow vapor to pass.

I've not really studied the early Chrysler vapor recovery systems but between the FSM and those Master tech booklets, you should be able to figure out what they did and how you can make use of them.

On my AMC wag I had to open up and replace the top filters of the charcoal canister since new ones are no longer avilable. Not the simplist system but something to consider if you have to.
Vapor Canister Rebuild - A new how to - International Full Size Jeep Association

 

[66 Valiant wagon]

If you say the clear plastic filter isn’t filling with fuel and then it’s dying that is your problem. Have you had the tank off?
My thoughts are it’s running rich on a first start up (assuming there’s a choke) and then as it leans out there’s not enough fuel to keep it running.