fuel bleed back
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Elder User
Joined: Dec 2007
Posts: 813
Likes: 6
From: Up Nort Minnesota
fuel bleed back
my 70 F250 w/390-4spd (4x4) loses all the fuel from the carb if it sits parked for a day. it's like it loses the fuel all the way back to the tank because you have to crank like crazy just to get fuel back up to the carb...
any thoughts or experience with this sort of problem?
any thoughts or experience with this sort of problem?
Postmaster
Joined: Sep 2004
Posts: 3,166
Likes: 2
From: wi
if i was a betin man id say its not runing back to the tank its more then likely runin down the intake and you have to crank so long cuzz its flooded. but try this any way install a see threw feul filter betweent the pump and the carb this way you can tell if thewres gas there or not
Post Fiend
Joined: Feb 2007
Posts: 7,191
Likes: 4
From: Blairsville,Ga
I had a similar problem with two later model vehicles,both '88 ford
after sitting overnight with no found external leak,even the primary fuel bowl had no das in it
knowing the gas from the bowl can't go back to the tank,but don't know where it did go
after sitting overnight with no found external leak,even the primary fuel bowl had no das in it
knowing the gas from the bowl can't go back to the tank,but don't know where it did go
Junior User
Joined: Oct 2007
Posts: 79
Likes: 0
From: Aromas, CA
Check the fuel hose under the cab. If its got a loose clamp or old hose, chances are its sucking air into the line instead of fuel! And visa versa when it sits(it drains). I would replace the fuel pump and filter while your at it!!
Senior User
Joined: Dec 2006
Posts: 281
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From: Woodstock, Portland, OR
Sometimes theres felt, I guess you would call them, O-rings that can go bad. I know on the motorcraft 2bbl carbs theres a pump in between the mixture screws in the bottom of the bowl. I don't know what this does, but i had the same problem and it was a broken gasket on this little pump. it will drain the carb of all fuel. I still have no clue where it goes.
Best bet, is to get a carburator re-build kit and FOLLOW THE INSTRUCTIONS and re-built it. Motorcraft Carbs are very straightforeward.
Best bet, is to get a carburator re-build kit and FOLLOW THE INSTRUCTIONS and re-built it. Motorcraft Carbs are very straightforeward.
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Elder User
Joined: Dec 2007
Posts: 813
Likes: 6
From: Up Nort Minnesota
It's a great big 4v carb about the size of a brigs lawn mower engine 
and it's definately dry, bone dry, no flooding problems here. and for the amount of cranking I have to do It acts like I ran the fuel tank completely empty when I shut it off & I have to pull fuel to the pump, then up the line, fill the bowl to the point my accelerator pump can give a shot of fuel... It's just really strange, it isn't like I'm just losing everything from the bowl & having to refill it, it's the whole line all the way back to the tank (which is a cab tank)
and it's definately dry, bone dry, no flooding problems here. and for the amount of cranking I have to do It acts like I ran the fuel tank completely empty when I shut it off & I have to pull fuel to the pump, then up the line, fill the bowl to the point my accelerator pump can give a shot of fuel... It's just really strange, it isn't like I'm just losing everything from the bowl & having to refill it, it's the whole line all the way back to the tank (which is a cab tank)
Fleet Mechanic
Joined: Aug 2007
Posts: 1,803
Likes: 243
From: Piney Woods of East Texas
If it's not a bad fuel line below the tank. I would remove the carb and verify all of the screws are tight that hold the base on. If it's a Holly with the side bowls they can leak at the base, too. Fuel can boil out when the engine is hot. You could also have a bad fuel pump. If a check is bad it can take a lot of cranking to get it to prime.
They way the needle and seats are setup, it will not bleed down to the tank. Unless your fuel line is below the bowl and the seat is loose. Other wise you have a air gap. The last time I checked you can not cyphon with an air gap. But the fuel line can leak in several places, pump and rubber hose connections at the tank. Way want to see if you smell gas in the oil.
They way the needle and seats are setup, it will not bleed down to the tank. Unless your fuel line is below the bowl and the seat is loose. Other wise you have a air gap. The last time I checked you can not cyphon with an air gap. But the fuel line can leak in several places, pump and rubber hose connections at the tank. Way want to see if you smell gas in the oil.
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