Vapor Lock / Gas Issues

[Mopar_Gods]

Took the 1977 Dodge Aspen 2 Door Coupe out last week got about 1 mile down the road and she shut down. I was able to get it off the road in a busy intersection thank god. Popped the hood and noticed that the clear fuel filter did not have any gas in it. Called the collectors insurance for a flat bed. Could not get it to pump or start cranked at least 15 or 20 times. Got home removed the fuel filter to see if blockage there was not any primed the carb it fired right up. I was like wtf. 1 hr on the side of road in 95 temp and get home and it fires up.

Went to take the aspen out today pulled it outside so the gas fumes would not kill my lungs started it let it idle for a few minutes and noticed the fuel filter beginning to fill up but then I noticed it looked more like it was boiling in the bottom of the filter more then filling the filter up if my eyes are working correctly. Let it idle till the gas in the filter ran completely dry again. Removed the top hose of the filter manually poured gas in it again and the fuel in the fuel filter ran completely dry again after just a few minutes.

The tank has a new fuel sending unit. The lines have all been replaced. The mechanical fuel pump has been replaced. The carb when the fuel filter does have gas in it when I move the choke manually I can see the jets on both spraying a nice solid stream of gas on both side. I have ran out of ideas. Any other feed back would be greatly appreciated she is aching to be driven more before the summer is over and my right foot needs sum throttle lol. Thank You

 

[Joe12459]

My son's car had terrible vapor lock issues. I ended up installing an inline electric fuel pump, and he's had no issues since then. Non-ethanol fuel also helps, as it has a higher boiling point.

 

[Aspen500]

Ethanol free fuel is important on a carbureted car, especially in hot weather. With EFI, the fuel is at high pressure which raises the boiling point so ethanol fuel or winter blend in the summer, isn't a problem. Sometimes helps to insulate the fuel lines to shield them from engine heat. Also, a thick carb base gasket will insulate the carb from heat transfer. As Joe said, a low pressure electric fuel pump is a solution that's been used since the Model A.

 

[BudW]

One item that is confusing: the accelerator pump circuit has about 3-5 pumps in it, when carburetor bowl is empty (ran dry) – so to check for an accelerator pump spray is not good to see if bowl is empty, or not.


An electric fuel pump and using a 3-line fuel filter (a fuel filter with the small return hose going back to the tank) should fix this problem.

The electric fuel pump "should" put out between 5 to 7.25 PSI – but no higher.
It is best to mount it by and under the fuel tank – but, in your case, it shouldn’t matter a lot.

Removing the existing (mechanical) fuel pump is needed as well as a fuel pump block off plate (pretty much all Mopar uses the same fuel pump block-off plate). A person could use one of those old pump bolts to mount the pump there and just use the existing plumbing.

One could hook the pump to the supply side of ballast resistor or use that wire to feed a relay to use battery voltage.
Just turn car on - but no crank for a second or two (for fuel pump to do its thing), tap throttle to reset its linkage and you should be good to go.

My ’86 5th Ave is getting hard to start after a long drive – which I suspect is not vapor lock but fuel bowl evaporation (hot soak) and it takes several moments for it to kick over – so have been considering adding (or replacing) the fuel pump in it, with electric.
BudW

 

[volare 77]

Running out of gas in one mile seems awful quick. Does it do the same with the gas cap loose? I`m wondering if your having a venting issue.

 

[BudW]

I miss-read that. I was “thinking” on a long drive.

Ventilation and/or a bad fuel pump, could be a factor, as well.
BudW

 

[Mopar_Gods]

I guess I will be installing a electric fuel pump was hoping not to half too, Would like to keep the mechanics of the vehicle original as possible. I do know this is not always possible. Had a few minutes to mess with it some more today. Cranked it today and noticed still no gas making it to the fuel filter even after cranking it over at least 20 times.

So removed the gas cap disconnected the top rubber hose to the fuel filter manually filled the filter with fuel and of course it started right up then put the gas cap back on. Weird sat there and watched this vehicle for a good 45 minutes and fuel filter stayed full.

In case I am wrong I am pretty sure if the mechanical pump was bad then surely the filter would of ran out of fuel before 45 minutes of the engine running even at just idle. Am still puzzled with it myself. Not sure if I am right but couldn't a gas cap with a bad seal cause to much suction to form and pull gas back to the tank from the fuel pump?. Just a thought I had.

Before I forget I did not notice any air bubbles or boiling or any kind of suction or drainage from the fuel filter this time around just stayed full for 45 minutes. Went back out there to look to see if fuel has drained back down from filter and it still looks almost full damn thing driving me crazy here.

 

[volare 77]

Have you double checked to make sure all the rubber fuel line hoses are in good condition? Sometimes they crack and you can`t see them. Also the hidden hose at the passenger side fender rocker location that connects the two fuel lines together. You can loose suction. Todays gas really seems to rot the rubber quickly. Your cap is not vented as thats why you have the charcoal canister to vent to for emissions. I do believe the cap does release excessive pressure at some point but I not sure when. If the car continues to run without the cap or a loose cap then not proper venting should be your answer. Your charcoal canister could be bad also.

 

[Mopar_Gods]

On the canister there is three ports. The one that says carb is capped off and always has been since I have owned the car. So don't know if that would be a problem think I have had the aspen a few years now.

 

[volare 77]

Some canisters come with a port blocked.

 

[Mopar_Gods]

Got up this morning and noticed now the fuel filter is holding gas just find almost full. I guess I can get a little jug and disconnect the line to make sure that the gas is pumping from the fuel pump also itself. Good thing is at least the gas in the fuel filter is not draining back like it was before. Ran it today about 2 miles and had no stalling issues and fuel filter stayed full. Will keep observing it, Thank You

 

[volare 77]

Hopefully you won`t have any more problems but issues like that usually just don`t fix themselves. Is the fuel pump a quality pump? I know you said the fuel lines are new but how new? I had a rubber gas line deteriorate in 6 months. I thought I needed a new fuel pump on my car and then realized the recently new hose had some small cracks in it causing my issue. BTW it wasn`t dripping gas but my pump couldn`t get suction. I`m still leaning towards it being a venting issue but draining back does makes me think there is a leak somewhere.

 

[BudW]

As far as cracked fuel hoses go – It is far easier to suck air than it is to leak fuel.
One would think it would do both – but not in most cases.

If a person has fuel problem – checking all hoses for cracks is one of first things to check for. If any are cracked – change hoses then retest, before doing anything else.

Mechanical fuel pumps have 2 check valves in them (performance ones have more). One check valve for inlet and one for outlet. If a piece of trash is caught in either check valve then the fuel pump has been rendered useless – until replaced or cleaned.

Trash normally/most likely comes from cracked fuel hoses.


In this case – I know at least 1 fuel pump check valve is working – sense fuel filter it holding fuel.

Note: I like clear fuel filters for diagnostic purposes but don’t care for them otherwise. Maybe because I’ve worked on too many underhood fire jobs before. I don’t know and there might not ever be any problem with clear plastic – but for some reason, I just don’t like using ‘em.
BudW

 

[volare 77]

I have seen too many of the glass fuel filters leak to leave one on my car.

 

[BudW]

I wasn’t referring to the glass filter – but yes.

I have a glass fuel filter, I bought back in the ‘80’s – lurching around in my garage somewhere. Hadn’t had any problems with leakage on it – but then again, it wasn’t on my 340, but for a year or so. I had a friend who broke theirs – without trying hard (over something silly, like dropping a screwdriver on it or something like that). I thought if something like dropping a screwdriver (or whatever it was) broke one then it wasn’t worth to keep on my car – so I changed it out with a metal one – and not looked back sense.

With that said, my lawn mowers have plastic fuel filters – but they also don’t have fuel gauges on them.
BudW

 

[MoparKidD-4]

It is quite possible you got a bad mechanical fuel pump. I got a replacement one from O'Reillys for my '70 Duster that only lasted about 8-10,000 miles before it quit. Then the replacement for THAT started seeping oil out from the area where the two "halves" are pressed together. Now I have yet another one that's still running on my 5th Avenue (the one that was on the car when I got it couldn't pump fuel at WOT), I'm not expecting that one to last forever either. If you want one that lasts get one of the nice aftermarket Holley etc. mechanical fuel pumps that you can take apart and rebuild. Fairly easy way to check if your pump is going south, disconnect the line going to the fuel filter and put it in an empty gasoline container. Start the engine and keep it running by carefully pouring gas down the fuel line into the carb (funnel with a small spout that fits in the fuel line helps). If the fuel pump is good it should shoot heavy streams of gas into the container with noticeable force. You can also time how long it takes to fill up a container to 1 gallon and compare that to the fuel pump's rated flow (usually in Gallons Per Hour).

Also this is probably a personal thing but I don't like letting engines idle for long periods, especially old-school engines with flat-tappet cams and carburetors. If I'm working on a fuel system issue, if it idles 3-5 minutes then I proceed to test-drive it. Better to spot the problem while driving since that's what the car is meant to do anyway, not sit in one place and idle... I've found a lot of problems that didn't show up unless the car was driving down the road. Idling uses very very little fuel, as I'm sure you are aware lol. Just do your test driving close to home and/or on back roads with no traffic so you can easily and safely pull over and lift the hood once the problem arises.

 

[BudW]

This is what a stock small block fuel pump looks like.

There is a crimp where the top half and bottom half attach – which also holds the edge of the diaphragm in place.

A poor crimp (red arrow) can cause a fuel leak, an oil leak or both.
The orange circle is to be a diaphragm vent and it can leak fuel, oil (or both) – if present (not all pumps have that vent).
The blue arrow is where the check valve(s) are located at.
The stock pump is not serviceable, except as an assembly.

This pump is rebuildable. Also, you can remove the screws (to middle to top or middle to bottom, to clock both the inlet and outlet fittings, as needed. Both the check valves and diaphragm are replaceable.
To date, I have not been inside of one of these pumps yet. I have clocked the fittings before – but not gone any further than that. Also – I hadn’t seen one of these pumps go bad yet (to date).

On the other hand – the stock appearing fuel pumps, I have replaced by the hundreds. I don’t know if the rebuildable style is worth the additional money – but does appear to have a better track record.

Also note: most of the performance fuel pumps/cars in the 60’s did come from factory with rebuildable style fuel pumps (including early 340’s).
BudW

Edit: the lower picture is for a big block. The pump is the same except for the arm (which is much shorter).