85 460 fuel problems.
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85 460 fuel problems.
Hey guys u have a 77 f150 with a 86 7.5 transplant. I currently have a new tank, new sending unit, flushed lines, new fuel filter,new mechanical fuel pump, and lastly new Edelbrock carb.
Basically with the truck running with over a quarter tank of gas the fuel filter will run dry, the bubble up, drain almost empty etc. Which leads me to think air leak in the line or malfunctioning fuel pump.... We checked all hose clamps and replaced and dry rotten hose today with same problem.
Any help or suggestions.
Basically with the truck running with over a quarter tank of gas the fuel filter will run dry, the bubble up, drain almost empty etc. Which leads me to think air leak in the line or malfunctioning fuel pump.... We checked all hose clamps and replaced and dry rotten hose today with same problem.
Any help or suggestions.
Cargo Master
Joined: Oct 2005
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From: NJ
Air leak, plugged filter, plugged fuel pickup sock in tank, bad fuel pump. Try running a rubber line off the suction side of the pump into a 5 gal can of gas to help pinpoint problem. If it doesn't keep flowing on that, put the output side of pump into a container and crank it, if you get weak or no flow you know it's the pump.
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From: Virginia
When it quits, pull the line off the suction side of the pump. If it's dry, you know the problem is from there back.
Have you noticed does it do it when the truck is started cold or does it do it only after it has run awhile and is warmed up? Does it do it when the truck is moving or only when it's sitting still? These clues will tell you if you have possibly run the exhaust system too close to the fuel line running to the rear.
Have you noticed does it do it when the truck is started cold or does it do it only after it has run awhile and is warmed up? Does it do it when the truck is moving or only when it's sitting still? These clues will tell you if you have possibly run the exhaust system too close to the fuel line running to the rear.
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Thanks for the replys, cadunkle ill do that test tonight. I feel the new fuel pump is working fine because if you lightly pinch the output line going to the carb with your fingers feel it pulsing/pumping fuel. But ill test it regardless.
Franklin2 it seems like it might get worse when its been idling for awhile but i can 100% confirm that because it seems erratic. The exhaust is mounted no closer then say 4 or 5 inchesat the closest point.
Yesterday i replaced a 2 sections of fuel line under the truck that seemed dry and could possibly been dry rotten. So at this point any rubber fuel line except the filler neck is brand new with new clamps.
Correct me if im wrong. Im almost 100% i dont have a air leak in the fuel lines, if there was something getting plugged up would it not stay plugged up?
Ill test the pump as soon as i can and post back later.
Thanks
Franklin2 it seems like it might get worse when its been idling for awhile but i can 100% confirm that because it seems erratic. The exhaust is mounted no closer then say 4 or 5 inchesat the closest point.
Yesterday i replaced a 2 sections of fuel line under the truck that seemed dry and could possibly been dry rotten. So at this point any rubber fuel line except the filler neck is brand new with new clamps.
Correct me if im wrong. Im almost 100% i dont have a air leak in the fuel lines, if there was something getting plugged up would it not stay plugged up?
Ill test the pump as soon as i can and post back later.
Thanks
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From: Virginia
I don't know how the stock 77 fuel line is run, but it sounds like you have replaced it with rubber hose. And I do not know how the stock 77 exhaust used to run, but I am leaning toward a bad combination of modified exhaust routing and modified fuel line causing the problem. I have seen it several times before, and rubber fuel line seems to aggravate the problem for some reason. If you have the exhaust running inside the frame, see if you can wire tie the fuel line on the outside of the frame. 5 inches is not enough if the exhaust and the fuel line are both on the inside of the frame.
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Alright looks like a combination of things were causing my problem. When i changed some of the fuel lines a few small rubber shavings got pulled into the fuel filter obstructing the flow. I tested the pump and cleaned it out. And finally i pulled the carb off and cleaned it.
So i now have good fuel flow! Seems to ve the simple things that will drive you nuts.
As a side note. Im getting the carb tuned in. I have a edelbrock 750 on it. Im getting a stumbling feeling on acceleration from 1st to 2nd but after that its drives great.
So i now have good fuel flow! Seems to ve the simple things that will drive you nuts.
As a side note. Im getting the carb tuned in. I have a edelbrock 750 on it. Im getting a stumbling feeling on acceleration from 1st to 2nd but after that its drives great.
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From: Virginia
You can download the instruction manual online from edelbrock's site. If it's stumbling when you nail the throttle, you might need a accelerator pump adjustment.
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Ya ive tried adhusting the accel pumpmore abd less. The "off idle stumble" they say the ims need to be adjusted leaner or richer. Lol. Im thinking possibly the vacuum advance might be giving me problems.
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Lead Driver
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From: Tennessee
Hard to get a good carb sometimes .
I have a buddy that went through 3 holley carbs on his SBC .I told him to get rid of them years ago .We put a Q'jet on it 2 months ago . Best it has run in 5 years ! 
I have a buddy that went through 3 holley carbs on his SBC .I told him to get rid of them years ago .We put a Q'jet on it 2 months ago . Best it has run in 5 years !
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From: Virginia
If you think it's the vacuum advance, unplug the line off the dist and put a screw in it to block it off. If you can tune it then and if the stumble goes away, you can then go from there. You can run it like that, it won't hurt anything but your fuel mileage a little bit. They make adjustable vacuum advance units you can install if it comes to that. You can also experiment with the timing. Nothing is written in stone now, the engine has been modified with a different carb and the emissions have been taken off, so different settings from the factory can give you better results. If you are setting the timing at the old 8 or 10 degree setting, unplug the vacuum advance hose, and set the timing up there at 12-14 degrees. I think you will be impressed with the difference. The engine will seem to accept that larger carb better with the timing advanced a little bit over stock.
Postmaster
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From: Broken Arrow , OK
Keep in mind the Edelbrock carb doesn't like more than 5.5 psi of fuel. You may be putting a lot more pressure to it than it likes. If the pump you are using puts out more than 6 psi you may want to get a fuel pressure regulator.
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Ive got the timing set at about 9.and it idles perfect. I took the vacuum advance hose off last night and sucked on it. (giggity) and it held vacuum and also i could hear the diaphragm working.
I will try blocking it off and adjusting the timing up. And ill check the fuel preasure.
I will try blocking it off and adjusting the timing up. And ill check the fuel preasure.
Cargo Master
Joined: Oct 2005
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From: NJ
Stumble on acceleration is most likely not enough accelerator pump shot or shot timing too late. Go larger on discharge nozzles or get more shot sooner. Not sure on AFB adjustment of that.
Could also be timing not advancing. Vacuum advance may only affect this if you're using manifold vacuum and even then it's negligible. Check your machanical advance. You said 9* initial, but waht is your total advance and at what RPM? Is it advancing quickly and smoothly? If you ahven't, I suggest cleaning and lubricating the mechanical advance.
Could also be timing not advancing. Vacuum advance may only affect this if you're using manifold vacuum and even then it's negligible. Check your machanical advance. You said 9* initial, but waht is your total advance and at what RPM? Is it advancing quickly and smoothly? If you ahven't, I suggest cleaning and lubricating the mechanical advance.
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Ok, yesterday with the motor at a idle i unplugged the VA and with my finger over the vacuum port i slowly reved the motor with success!
I advanced the timing to ruffly 13 and its actually drivable now. I still have a little hesitation/stumble right off idle but it clears out fairly quick when driving. Im sure with some additional tweaking i can get it better.
A new vacuum advance bulb is like 40$ and a complete distributer assembly is almost the same.
Ill order one shortly and hopefully be done with this. :-)
I advanced the timing to ruffly 13 and its actually drivable now. I still have a little hesitation/stumble right off idle but it clears out fairly quick when driving. Im sure with some additional tweaking i can get it better.
A new vacuum advance bulb is like 40$ and a complete distributer assembly is almost the same.
Ill order one shortly and hopefully be done with this. :-)