Having strange issue I can’t figure out. If my f100 sits for a few days the carb bowl will be empty. Takes a ton of cranking to get it going again. Visibly I can’t see any fuel leaks. Trying to find a place start looking.

PO had a great fix. They had a electric fuel pump with switch I dash. Told me to turn on for 10-15 seconds before starting for first time in few days.

 

Where do you live? Does the fuel have a high percentage of ethanol? Do you have an open element air cleaner?
What carb, what engine, how's it run otherwise?

Paul

 

I live in San Diego.

Stock Air Cleaner.

Motorcraft 2bbl carb, 352. Runs like a champ. I can start it up same day all day no problems.. and sometimes a day or two later.. its just for anything more than a few days and the bowl is dry.

 

Behind the seat tank or frame mounted? How much fuel?

 

Behind the front seat. Not sure the capacity

 

Mine does this too. Trying to figure out why it syphons back out of the carb. Maybe it need some kind of ball-valve thing in the line to keep it from drawing back out of the carb.

 

I want to say the tank behind the seat is 18-18.5 gal. I’ve noticed mine does this with less than 1/2 full. When it’s full tank. I added a electric fuel pump and it’s better but not completely cured, still harder to start with less than 1/2. Maybe a check valve would help if the fuel is draining back into the tank

 

What I dont see is how it would drain back in the tank. The fuel flows into the top of the carb bowl.

 

The fuel in carb cannot be siphoned physically not possible. So you have two problems. The fuel in bowl may be evaporating or a low float level causing a slow start. I do believe that your fuel pump is allowing the fuel in the line to be siphoned back to the tank. Causing the pump to have to prime and fill before supplying fuel to carb. Check your float level and check fuel pump by putting fuel gauge on line after pump start truck and let it run until it dies. Note the pressure and how long it holds it before it bleeds off. It should hold for awhile if it does not then your pump should be replaced or a check valve installed close to the tank as possible.

 

Once gasoline goes through the inlet needle and seat into the float bowl it ain't going to go back to the gas tank. It might leak out, it might evaporate, it might just go stale and act like it's not even there. If it has alcohol, it might have water in it and if the water sinks to the bottom of the float bowl, that's what the jets see. Putting any valves in the fuel line will have no benefit.

 

I run 87 octane, plain 10% ethanol fuel in my 71', and if I leave the truck alone for 2 weeks (parked at the airport) the fuel will evaporate from both the front and rear bowls on my Holley 600cfm. Having the electric carter fuel pump primes the bowls quick and starting after sitting is a non issue. The newer gas has its flaws with ethanol, but what can be said is that the days of old gas varnishing in the fuel bowls are over.

 

I see two likely causes for this. Either your fuel is evaporating, or the power valve is blown and the fuel is seeping out and going down into the engine.
Most likely evaporation is the issue here, and with today's fuels that is to be expected.
An electric pump to prime it, is the easiest fix, and also is a decent, anti theft device as long as the switch is hidden away, out of sight.
My old 78 one ton, has an old oil bottle under the hood, with a pint of so of gas in it. I pull the air cleaner lid off and pore a little in the carb, and put the lid back on, if its sat very long. It fires right off, and I don't have to spent the money on an electric pump, on a truck that gets driven 200 -300 miles a year.

 

Ethanol fuel evaporates faster than fuel did back when our trucks first were on the road.
Now add heat from the motor with the carb sitting right in the middle like on a v8, a six the carb sits off to the side and not as much heat.

Also as pointed out there is no way fuel from the carb fuel bowl can drain back to the tank.
Gas would need to flow up into the needle to do this.

I bet when it gets hot out and you drive then stop for a bit it is hard to restart?
Again it is the Ethanol fuel boiling in the carb. Remember it is sitting over heat.
The fuel boils and the fumes being heavier than air in drops to the intake floor and floods the motor.
I bet when it then starts it acts like it was flooded and once it clears runs great.
If you do a search in any of the old truck areas for hard restart when hot you will see any motor running a carb has this problem.

They say putting a little diesel fuel in with the gas, no more than 1 gallon diesel to 20 gallons of gas but start off low and work up.
It makes the molacules change so itdose not evaporates or boils as easy.

BTW I have the hot fuel boil / hard restart and sitting for more than a week needing to crank for along time.
No I have not added diesel as it dose not bother me that much to add it as fill ups.
Dave ----

 

I may just start filling with 100 Low Lead if that’s the case. I’m at my airport few times a week. So it’s easy.

 

Oh yes, 100 low lead would work great, as its probably pretty close to what these old engines were set op to burn in their glory days.

I have used it, and still do, in my small engines, and it has virtually stopped all of my carburetor troubles that I had before. Weed eater, leaf blower, chain saws, generators, tiller, and my push mower, all run low lead.

However, I wont run it in my trucks, and old car for a couple of reasons.
First, is the cost, at almost twice the cost of pump gas, and with the large appetite for fuel these old engines have, it would get expensive real quickly.

Second, is this fuel has no road tax, and would be some kin to running off road diesel in your diesel powered truck, a violation that carries a huge fine.
The chance of getting caught is almost non existent, but if you did, it would be a real kick in the nuts.

The previous air port manager we had, at our small air port would not sell low lead to you for the above reason. That is if he was there....So we had to get it when the assistant was there, when we wanted it.
A few years ago, they put in a pay at the pump, and my buddy is a pilot, so we can get it now, when ever we want it. The new manager don't seem to care, anyway, but its just easier to go in the evenings when the air port is closed.
I keep a couple of 5 gal cans of this around all the time, and it will not go stale, like pump gas does.

Regards,
Brad