Guru's please help: Glass Filter at Carb going empty

[Ensane13]

Bare with me here because I don't know all the correct jargon and have a limted knowledge of most things engine related (I have a few guys helping me out that are very smart in these fields)
I have a 75, 302 with cam and gear driven, intake and holley 4 barrel. I finally have it on the road and she ran fine in the winter. Now being warmer after about ten minutes the glass filter at the carb emptys itself of fuel (idols fine but dies under a load).
Here is a list of things done and replaced. First isse I had in the winter was that the encentic was loose so that was taken care of and I got about a month of no problems. Happened again and is still happening after replacing all hoses, filters,gas tanks and fuel pumps (it is a mech pump)(we also took motor apart and checked encentic again to be sure and it was tight and fine). I was told maybe vapor lock but we ran it straight from a gas can plumbed into the fuel pump with same results. We then iced the carb and ran water over the intake because it seemed the carb was getting way too hot and that seemed to give some of the fuel back. So next replaced the 180 thermostat with a 160 and I added a 1/2" phenolic spacer to help with the heat issues and still the same result. Now we are kind of stumped and any advice would be great. I am sure I have missed a few things and I will try to answer any comments the best I can.

 

[asinor]

The strainer in the tank may be clogged.
You may have another fuel filter inline somewhere that is clogged.

If its getting sucked dry, then its not getting enough fuel for some reason.

 

[Ensane13]

all new everything (filters, lines, tanks). plus i ran it right out of a gas can into the pump with same result. leaning towards the heat issue because water on the intake and ice on the carb made it fill back up a little bit

 

[Ensane13]

the guys helping me out are thinking the fuel could be getting to hot and evaporating at the carb and causing it to go dry in the fliter?

 

[broncodriver99]

I had the same problem and it was the fuel pump. I see you have replaced that. Could you have a loose line that could cause it to suck air? It's either that or something is wrong with the fuel pump.

 

[73azbronco]

First, what is your fuel pressure? Idle? 2000 rpm?

If the pressure is low, you might try a cheap electrical pump which bypasses the mechanical and see what that does.

When is the last time the carb was rebuilt/opened?

 

[Rustytruck]

Its probably sucking air in through the valve at the floor board since you replaced all the lines. take the cap off the valve and replace the o-ring.
the system sucks air in and mixes with the fuel being pumped. once you shut it off the fuel runs down the line as the bubbles that were in suspension while being pumped now float up to the top of the line and into the filter. The check valve in the pump should keep the whole line from draining and only the pressure side of the line should the bubbles float up. Is your fuel filter higher than the float level in the carb if so it will also drain into the carb as the fuel in the carb bowl evaporates when the motor is shut down it opens the needle and seat and any fuel above the needle and seat will drain down. Ford didn't design the fuel line higher than the needle and seat but through the years people add their own fuel lines and filters and what was stock is no longer the same as when it left the factory.

 

[Monster Mike]

I had this same problem on my 74 hiboy. Mine only had one tank so that eliminated the selector valve being an issue. We came to the conclusion that the eccentric was installed improperly or the wrong eccentric was installed. This was determined after the 3rd new mechanical fuel pump was installed. All the pumps worked but every time it was under load over 2000 rpm it would kill the motor. Installed a $45 electric fuel pump from autozone & the problem disappeared completely.

 

[Ensane13]

First, what is your fuel pressure? Idle? 2000 rpm?

If the pressure is low, you might try a cheap electrical pump which bypasses the mechanical and see what that does.

When is the last time the carb was rebuilt/opened?

carb was just rebuilt as well

 

[Ensane13]

Its probably sucking air in through the valve at the floor board since you replaced all the lines. take the cap off the valve and replace the o-ring.
the system sucks air in and mixes with the fuel being pumped. once you shut it off the fuel runs down the line as the bubbles that were in suspension while being pumped now float up to the top of the line and into the filter. The check valve in the pump should keep the whole line from draining and only the pressure side of the line should the bubbles float up. Is your fuel filter higher than the float level in the carb if so it will also drain into the carb as the fuel in the carb bowl evaporates when the motor is shut down it opens the needle and seat and any fuel above the needle and seat will drain down. Ford didn't design the fuel line higher than the needle and seat but through the years people add their own fuel lines and filters and what was stock is no longer the same as when it left the factory.

I removed the valve in the floorboard for now and I am only running it on the side tank. I believe my filter is below the floats but i am not completely sure.

 

[Ensane13]

I had the same problem and it was the fuel pump. I see you have replaced that. Could you have a loose line that could cause it to suck air? It's either that or something is wrong with the fuel pump.

I am on my second new fuel pump now and leaning towards putting in the electric if it will fix this issue.

 

[Ensane13]

First, what is your fuel pressure? Idle? 2000 rpm?

If the pressure is low, you might try a cheap electrical pump which bypasses the mechanical and see what that does.

When is the last time the carb was rebuilt/opened?

I am also not sure of the pressure. I can check with buddies and see if anyone has something to test that and get an answer for you.

 

[TwoDalesDad]

I would look for a filter that is plugged. Or a leaky fuel line in line. Your bigger problem is the fact ......you are running a glass filter!! ..i have had in my many years a few trucks....vw.'s burn due to the glass filter's......a cheap fix is a throw away...plastic.....or metal filter....spend a couple of extra bucks on a filter that won't cause a fire if it gets rattled .....then back to starving for fuel problem.....

 

[Timmy390]

Your bigger problem is the fact ......you are running a glass filter!! ..i have had in my many years a few trucks....vw.'s burn due to the glass filter's.....

100% agree. No matter what you do get rid of that firestarter.

Tim

 

[Ensane13]

I would look for a filter that is plugged. Or a leaky fuel line in line. Your bigger problem is the fact ......you are running a glass filter!! ..i have had in my many years a few trucks....vw.'s burn due to the glass filter's......a cheap fix is a throw away...plastic.....or metal filter....spend a couple of extra bucks on a filter that won't cause a fire if it gets rattled .....then back to starving for fuel problem.....

I bypassed everything and ran a brand new hose out of a gas can sitting on the fender with the same results. Also of course brand new lines from the pump to the carb. As far as the glass filter goes if thats a bad idea I will remove it. I don't need to add fire to my list of things going wrong

 

[carmi]

You might try a vaccuum gauge (Mighty Mite?) used for bleeding brakes and such to determine if there is a lot of resistance from the tank to the pump. Mechanical pumps are very efficient at pushing fuel but can run into proplems if there is to much resistance from the tank and lines. Make sure your fuel lines are far away from any exhaust and other heat sources. It doesn't take much to cause the fuel to boil. I have always used a glass fuel fillter and have never had any problems. I like to be able to quickly check the fuel flow and keep an eye on any build up in the screen.

 

[Ensane13]

You might try a vaccuum gauge (Mighty Mite?) used for bleeding brakes and such to determine if there is a lot of resistance from the tank to the pump. Mechanical pumps are very efficient at pushing fuel but can run into proplems if there is to much resistance from the tank and lines. Make sure your fuel lines are far away from any exhaust and other heat sources. It doesn't take much to cause the fuel to boil. I have always used a glass fuel fillter and have never had any problems. I like to be able to quickly check the fuel flow and keep an eye on any build up in the screen.

yeah mine was on from the PO and I thought it was a quick check option as well. If it wasn't for that at the moment I wouldn't know the fuel was dropping. I will check into the gauge

 

[HoosierDaddy]

My fuel pump issue was the pump diaphragm leaking fuel into my oil ... a bunch of it.
I'm glad I didn't drive it , i caught what was happening while it was idling after i had just started it after its long winter storage nap.

Went electric after that , the shoddy way stuff is made today , I didn't care to worry about toasting the innards of the motor because of a cheap-ass mechanical fuel pump.

I am running a Carter 4070 (iirc)low pressure , about 5 or 6 psi , supposed to be a really good pump , on both of my Broncos now.

 

[Ensane13]

My fuel pump issue was the pump diaphragm leaking fuel into my oil ... a bunch of it.
I'm glad I didn't drive it , i caught what was happening while it was idling after i had just started it after its long winter storage nap.

Went electric after that , the shoddy way stuff is made today , I didn't care to worry about toasting the innards of the motor because of a cheap-ass mechanical fuel pump.

I am running a Carter 4070 (iirc)low pressure , about 5 or 6 psi , supposed to be a really good pump , on both of my Broncos now.

So when you are adding this electric pump I take it you are also removing the mech one?

 

[ryansbronco]

I quickly read this so this may have been asked before.
Do you have the fuel filter pointed the correct direction?
there should be a arrow that would be towards the carb.
If it is mounted the wrong way fuel wont flow well.

the stock screw in filter work just as well and may be cheaper