Loosing fuel pressure

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aa-1159

aa-1159

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73 Duster 360, 650 Brawler double pump, mechanical secondary
6 lbs fuel pressure at start up, starts dropping slowly to 3 or less after 10 min run time, new fuel pump, new rubber lines, 3/8 fuel line
Tank is vented
 
aa-1159 said:
73 Duster 360, 650 Brawler double pump, mechanical secondary
6 lbs fuel pressure at start up, starts dropping slowly to 3 or less after 10 min run time, new fuel pump, new rubber lines, 3/8 fuel line
Tank is vented
Click to expand...
I had a similar issue (mine would drop, I adjust it then eventually it would go up again so I would adjust back down). I ended up thinking it was a bad gauge, replaced it and found it to be the gauge port on the regulator. Now I run 2 gauges. One on the regulator and one on the fuel log just to be certain.
 
AJ/FormS said:
Mechanical pump?
Dead-headed regulator?
What happens if you rev it up a bit? say 1000rpm.

BTW
on the street, 3psi is lots, so long as delivers the volume.
Click to expand...
Pressure never goes up
Always stayed at 6psi until lately
New mechanical fuel pump
 
I have had this issue with both of my cars. My 71 Challenger it was the fuel filter causing it. What type of filter are you using? Mine was an Earls in line filter with changeable element. There are screens on both ends of those and they can get waded up under hard acceleration and stop the flow of fuel, needless to say it went in the trash and I put an Edelbrock filter on it. Been fine since.
My Duster on the other hand....
3 fuel pumps
2 filters
3 sending units
1 new metal line from the tank
Not sure what actually fixed it but, it seems fine now. It really seemed to go away after the last sending unit and new metal line from the tank.

Good luck!! Let us know what ya find.
 
plymouth4onthefloor said:
dirty sock in the gas tank, worn cam lobe/ pushrod
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Small blocks don't use a pushrod off the cam to pump the fuel pump. They have acentric on the snout of the cam. If it starts out with fuel pressure then loses it after running for a bit, I doubt it is that.
 
plymouth67 said:
Small blocks don't use a pushrod off the cam to pump the fuel pump. They have acentric on the snout of the cam. If it starts out with fuel pressure then loses it after running for a bit, I doubt it is that.
Click to expand...
you're right, my small block rebuild is 27 years ago, had a mix with my BB.
 
You know what; my 400hp/367 doesn't even have a fuel pressure gauge.
Nor a quality oil-pressure gauge,
Nor a quality coolant temperature gauge.
All my car has is the factory slow gauges that are about as forthcoming as a pregnant wife.
Gauges are just tools. Build your systems with confidence, and you won't have to monitor them.
The carb doesn't actually care about fuel-pressure. It only cares about the liquid level in the bowl. As long as the bowl is full and stays full, everything is golden.
 
Maybe trying blowing some air backward through the fuel line to clear out the sock filter in the fuel tank. If it runs normal after that, for a while at least, then you know it's at least related to a restriction somewhere BEFORE the fuel pump. It's possible you also got a defective new fuel pump. I just replaced my mech pump with a Carter Street/Strip mech pump for the same reasons as you're describing. Holding steady at 6psi now.
 
I had this same problem with my 360 in my 72 duster and with today’s fuel with higher ethanol content the fuel was vaporizing. I installed a bypass regulator and never had the problem again. To return the fuel to the factory tank I welded a bung in the filler neck and the unused fuel dumps right back into the tank.

IMG_9349.jpeg


IMG_9342.jpeg
 
Jim Ward said:
I had this same problem with my 360 in my 72 duster and with today’s fuel with higher ethanol content the fuel was vaporizing. I installed a bypass regulator and never had the problem again. To return the fuel to the factory tank I welded a bung in the filler neck and the unused fuel dumps right back into the tank.

View attachment 1716269613

View attachment 1716269614
Click to expand...


I think if nothing changes fuel wise and you are making any kind of power you’re going to need a return style regulator.

A block mounted fuel pump gets as hot as every other part of the engine and that causes grief too, not considering all the rest of the issues from todays fuel.

I think it’s a necessary evil at this point. Especially if you live where it’s hot.
 
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