Fuel problems
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Junior User
Joined: May 2004
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Fuel problems
Hello everyone....I posted this thread a few months back and had no luck with it so im going to try it here.......I was given an 85 F250 4wd with a 460 in it and 4 speed from my father in-law......It has a fuel problem that is ****ing me off....The carb will take gas from the front tank with no problem...As soon as you turn on the rear tank it floods the carb........My inlaws took it to a mechanic and he couldnt figure it out.....He lowered the float levels in the carb.....When the carb is running off the front tank i can run the carb out of gas on small hills.....With the carb running off the rear tank i can pull hills no problem even with a 7 thousand pound camper behind me......But if i have to stop or slow down the rear tank floods the carb..........If anyone has any info i would appreciate it...........Thre front tank has 2 lines going to the tank selector valve.....The rear tank has 2 lines going to the selector valve.....and there are 2 lines going to the carb.........Please help!!!!!!
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
Here's what comes to my mind...
Maybe the front tank fuel pickup, filter or fuel line is clogged and the carb is adjusted to make up for that. Switching to the rear tank with good fuel flow floods it.
Take the fuel line off the carb and put it in a can. Turn the engine over with the front tank selected and then with the rear tank. Compare the fuel flow between the two.
Do this test with the gas caps off, too. Maybe the front cap isn't letting enough air in or the rear cap is allowing too much pressure to build up. Switch caps and try it again.
Is there an electric fuel pump on either tank?
Just a few thoughts.
Kevin K.
Maybe the front tank fuel pickup, filter or fuel line is clogged and the carb is adjusted to make up for that. Switching to the rear tank with good fuel flow floods it.
Take the fuel line off the carb and put it in a can. Turn the engine over with the front tank selected and then with the rear tank. Compare the fuel flow between the two.
Do this test with the gas caps off, too. Maybe the front cap isn't letting enough air in or the rear cap is allowing too much pressure to build up. Switch caps and try it again.
Is there an electric fuel pump on either tank?
Just a few thoughts.
Kevin K.
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
You could try switching the pumps. Maybe the rear pump is too powerful and is blowing the needle out of the seat in the float, and causing the problem. If the rear pump is for a FI engine, it'll have too much pressure for a carbed engine.
Also, has the carb been rebuilt recently? Could be the needles and seats need replacing.
Again, just making some guesses here.
Kevin K.
Also, has the carb been rebuilt recently? Could be the needles and seats need replacing.
Again, just making some guesses here.
Kevin K.
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Junior User
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I just went out and isolated both pumps and they both have the same flow.......if the tank selector valve isnt letting extra gas return to the tank they would cause it to flood to wouldnt it..........
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
I don't know if the selector has a bypass like that. As far as I know, that's usually in the pump.
You could try bypassing the selector by running a line from the pump straight to the carb.
What kind of carb are we talking about?
You say there are two lines going to the carb from the selector. Do they ever meet or do they go into the carb in two different places?
K.
You could try bypassing the selector by running a line from the pump straight to the carb.
What kind of carb are we talking about?
You say there are two lines going to the carb from the selector. Do they ever meet or do they go into the carb in two different places?
K.
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Junior User
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Just before the carb they join together in a little cylinder about 3 inches long.........Its the stock motorcraft four barrel.......
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Junior User
Joined: May 2004
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I bypassed the tank selector valve on the return side for the rear tank and the truck ran fine........So that means it is either clogged between the fuel line on the frame rail and the tank...........according to the book the tank selector valve is a rotary valve so i dont think that it is the valve
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