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Discussion Starter · #1 ·
My 400 in my 79 Bronco runs excellent but I am having problems with the fuel filter getting clogged up. It is a clear inline. I can drive it around and runs good put then I can pop the hood and after awhile I can watch the filter go empty. Filter has trash in it but don't look like enough to clog it. When I take it off and clean it I am ready to go again. Filter will stay completely full again for awhile. I blowed air into the line going to the tank with the fuel cap on, the gas that came back up the line was clean and clear. So I think my problem is the hard line coming form the pump to carb. When I check for fuel from this line the fuel is rusty colored. I also kinda thought about the idea that it might be vapor lockin but im not sure. I replaced fuel pump to make sure that wasent the problem.
 

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My first thought is vapor lock. Put some pipe insulation around the fuel line, particularly forward of the firewall up to the carb.
 

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Discussion Starter · #3 ·
I cut off part of the hard line today and replaced it with rubber fuel line and have the line far away from any metal on the motor. I still have the same problem with the filter going emtpy. This time it seemed to take longer to do it. It only goes emtpy after the engine has been drove and is up to operating temp. The lines are clean and the filter is clean so it isnt trash. Sometimes when it starts to go emtpy I start to see bubbles getting pumped into it, still signs of vapor lock? Or maybe I have a bad fuel pump? If I let the truck set about 10minutes and cool a little as soon as I crank it back up the filter goes completely full untill everything gets warmed back up.
 

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Sounds to me like your fuel pump is going out. When it heats up all the parts are expanding and allowing it to cavitate and not pump.

Later
RK
 

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Discussion Starter · #6 ·
I have put 4 fuel pumps on it within the last 2 weeks, I guess I still aint got a good one yet? All the lines are clean and I blowed air through the line going to the tank. Could I have a larger piece of trash that may be getting sucked up against the pickup tube? Thanks for the help. It is very annoying not to be able to drive my Bronco, lol.
 

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Could be a piece stuck on the fuel pickup in the tank but I wouldnt know why it only gets sucked up when the truck is warm.

I am guessing the pumps you have been putting on are from a yard not rebuilt or new?

I am sure with the smart guys on here it can be diagnosed and fixed.

Later
RK
 

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Discussion Starter · #8 ·
I got the pumps from Advance. They are a brand called AirTex, which I have never heard before. I need to find a place that sells common name brand fuel pumps.

I have pretty muched ruled out trash. Because I only have the problem after the truck is at normal operating temp. As I said before fuel filter is clear and free of trash. Thanks for helpin me out.
 

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What about putting on a cheap electric fuel pump to see if that fixes it. Will rule out the mechanical pump question.
 

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Discussion Starter · #10 ·
I could try that. Im thinking that is my only option right now. How hot do the lines have to be to have vapor lock? I re-routed lines and moved them further away from metal on the motor. The hard lines are warm to the touch, but nowheres near hot enough to burn you. Pump doesnt feel abnormally warm either. I figure vapor lock isnt my problem after looking over everything again and seeing how it is doing.

When the engine is cold and I crank it up filter goes full. Turn the motor off filter stays full. After the motor is at operating temp fuel filter goes dry as soon as the engine is turned off.
 

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Have you checked all the lines, to make sure they are not cracked or sucking flat?
I put a new fuel pump on for a friend and his was doing the same thing, still did it after the fuel pump, so I crawled under while he reved it and then I could see the crack in the line going into the pump. Put on a new fuel line and it worked great.

It wasn't leaking any fuel from the line, so all I could figure is that it was sucking air through it. :scratchhe
 

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Discussion Starter · #12 ·
I kind of thought of the samething but what has me stumped is that the problem only occurs after everything is warmed up. If there are cracks in the line wouldn't the pump try to pull air through them all the time? I will check though and I will check and see if the fuel line is collapsing.
 

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My 400 in my 79 Bronco runs excellent but I am having problems with the fuel filter getting clogged up. It is a clear inline. I can drive it around and runs good put then I can pop the hood and after awhile I can watch the filter go empty. Filter has trash in it but don't look like enough to clog it. When I take it off and clean it I am ready to go again. Filter will stay completely full again for awhile. I blowed air into the line going to the tank with the fuel cap on, the gas that came back up the line was clean and clear. So I think my problem is the hard line coming form the pump to carb. When I check for fuel from this line the fuel is rusty colored. I also kinda thought about the idea that it might be vapor lockin but im not sure. I replaced fuel pump to make sure that wasent the problem.
so your not having any running issues? hot or cold? ignore the filter, does it run fine after it is hot and parked for 5 minutes?
 

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I bought several pumps from Advance and all of them gave me problems. 2 of them had TOO much pressure and the other didn't make enough, finally went to O'Reily's and got one from them and it worked fine. I'd find another source.
 

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Discussion Starter · #15 ·
so your not having any running issues? hot or cold? ignore the filter, does it run fine after it is hot and parked for 5 minutes?
Runs good hot or cold. Starts good hot or cold. I just turn it off when I see the filter go dry so It wont suck the carb bowl dry. After it cools a minute I start it up and the pump will start pumping again.
 

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Discussion Starter · #16 ·
I bought several pumps from Advance and all of them gave me problems. 2 of them had TOO much pressure and the other didn't make enough, finally went to O'Reily's and got one from them and it worked fine. I'd find another source.
I had a similar problem on my 79 Ford Pickup. Went through many few pumps before I got a good one.I also went through 5 carburetors before I got a good one. I think im going to get the next fuel pump for the Bronco from O'Reilys also. I have had lots of problems with products from Advance.
 

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How high up over the manifold plane (level) is the (inline, glass ?) fuel filter,
and consider getting a fuel line regulator for carburetion, not fuel injection.
Youll find that a fuel regulator (set at about 3 to 5 pounds) will calm some problems
with cheaply rebuilt carburetors.
 

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......also one of those inline fuel pressure gauges will help, so what works for me is , line up from fuel pump, then the glass filter, then the regulator, then the inline pressure gauge then connection to carb.
Just my 2 cents.
P.S...getting your steel line away from the block helps
somewhat also.......:toothless
 

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Runs good hot or cold. Starts good hot or cold. I just turn it off when I see the filter go dry so It wont suck the carb bowl dry. After it cools a minute I start it up and the pump will start pumping again.
so everything is fine, except if you shut it down and try to restart is right away it fails?
 
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