I drive my truck everywhere without a hiccup until today.
Of course yesterday symptoms showed themselves.
While doing a couple of bike pickups I noticed my mileage dropped from a normal 18.5 MPG (for me) and I had to put 5 gallons in when I should have had enough for the day. That and the smell of gas made me have a look this morning before taking off. Nothing out of the ordinary so off I go.
5 miles later while getting off the freeway it stalled out. I restarted with a lot of cranking and my foot to the floor due to a stronger gas smell. Got her going and went the 2 blocks to the shop and shut her off. Here is what I found.
Gas streaming out of the lower section of the carb parallel with the butterfly valve and down onto the exhaust manifold . When restarted the gas vanished while running but the engine would not idle, bog down and die and out the gas would flow
Things I observed over time:
Engine always hard to start when hot that requires extended cranking.
Mechanical fuel pump delivers unusually high pressure (to me) because when I replaced the fuel hose a couple months ago I was surprised of the amount of fuel that sprayed out when I took off the hose.
Engine is a 300/6 in a 1970 F100.
Carter carb with auto choke.
Wadda Ya think?

 

I would guess that the higher fuel pressure would be caused by a restriction of some kind. Just like putting your thumb on the end of a garden hose, pressure goes up. But I don't know for certain. But that big yellow truck looks sad on that wrecker.

 

The normal fuel PSI is like 4-6 lbs so you should get a good amount if the vehicle carb float needle valve is good an holding.

It sounds like the carb accelerator pump diaphragm is leaking. Time to rebuild it or have it done is best. A loco Box store you never know if you'll get a keeper the first time.
You may get away with just replacing the accelerator pump diaphragm. But if the carb has never been rebuilt as fas as you know then, I'd say it's time for a complete overhaul on the carb.
Orich

Orich

 

sounds like what my carb did after something went wrong with a rebuild. It was like a fuel fountain! Definitely start with a carb rebuild.

 

Well I can't blame anyone else on the rebuild. I did it over a year ago.
Thanks for the tip on the accelerator pump. I'll look there first.

 

If you wiped an extra coating of something on the gasket there that coating could have given way. If there is a restriction as mentioned above the pressure could be higher than the needle and seat can handle to shut off fuel flow. Or the float sank and it's got gas inside of it. The needle and seat are above the float.

 

My leak is down at the bottom a
I'll try to open it up tonight
I'll keep you updated

 

Put a new accelerator pump unit in along with a new rubber tipped float needle.
It idles nice but still flows fuel after shutdown
I don't want to buy a new carb but I'm stumped.
I wanted to pick up my next bike project tonight but I might miss out on it.

 

What did you set the float setting at ? it may be to high.
Orich

 

Might have a piece of crude in the needle and seat from when you replaced the fuel line.I have seen it happen on a 2 barrel carb.

 

Float level good.
I'll check the seat tomorrow.
Thanks

 

A few pictures would help where the leak is as this is kind of a guessing game not seeing ..
Orich

 

I think he's talking about where the 9516 gasket is in my pic above Rich. The only thing I can think of is there is either a crack or a porous spot in the carb body that makes it look like that 9516 gasket is leaking.

 

Wonder if gas is wicking out the 9581 shaft like when they get warn to much.
I've only rebuilt one of these about 20 yrs ago. an can't think of other then a high float or acc. pump leaking..
Orich

 

Alrighty then. It's always the simple stuff!
Pulled it apart again and this time looked where the float needle seat screws into the carb top. A whole lot of crap was stuck in there so when there was fuel pressure it would keep the needle from seating. Cleaned it up and problem solved.
Sorry to waste everybody's time with something I should checked first.
Live and learn.