fuel pressure dropping over time

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allright gents, this is where we're at

i took apart the regulator and found 2 potential issues

this is a "reference style" adapter which means there is a small nipple that can be fed by engine vacuum or blower boost to decrease or increase fuel pressure

i dont need it, it just came with it

per the instructions, i left this barb open, vented to the atmosphere
upon inspection i found a tiny pebble (i think it was a pebble, i pushed it out with some wire and it disappeared)

i cant imagine it did much, but who knows
i got it out and put a vacuum cap on there for now


the second "issue" i found was one of the fittings (the one that feeds the carb, in fact) had more thread engagement then necessary and was protruding into the well of the regulator

it didnt look like it would interfere with anything, but i thought it might cause some issues, so i trimmed that down and reinstalled it


no idea when i get another chance to drive it, but we will see if it did anything
 
Hopefully that’s it. Leave the port open to atmosphere so it will compensate for barometric pressure changes. It will give you more stable fuel pressure. Capping it does exactly what the pebble was doing.
 
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diymirage said:
allright gents, this is where we're at

i took apart the regulator and found 2 potential issues

this is a "reference style" adapter which means there is a small nipple that can be fed by engine vacuum or blower boost to decrease or increase fuel pressure

i dont need it, it just came with it

per the instructions, i left this barb open, vented to the atmosphere
upon inspection i found a tiny pebble (i think it was a pebble, i pushed it out with some wire and it disappeared)

i cant imagine it did much, but who knows
i got it out and put a vacuum cap on there for now


the second "issue" i found was one of the fittings (the one that feeds the carb, in fact) had more thread engagement then necessary and was protruding into the well of the regulator

it didnt look like it would interfere with anything, but i thought it might cause some issues, so i trimmed that down and reinstalled it


no idea when i get another chance to drive it, but we will see if it did anything
Click to expand...


Hook that nipple to ported vacuum. It will slightly reduce fuel pressure at a cruise.
 
diymirage said:
what would be the benefit of that?

or does that mean it would come up a bit under load?
Click to expand...
It would lower the fuel pressure according to vacuum. Cruise-high vacuum=lower fuel pressure. Wide open-low vacuum=atmospheric pressure in the regulator and fuel pressure will be what you set it to while the hose was disconnected.
 
TT5.9mag said:
It would lower the fuel pressure according to vacuum. Cruise-high vacuum=lower fuel pressure. Wide open-low vacuum=atmospheric pressure in the regulator and fuel pressure will be what you set it to while the hose was disconnected.
Click to expand...
this is just not jiving in my mind
right now, pressure is dropping, so im gonna hook it up to vacuum to drop it even more?

(not that i am opposed to trying it, i just dont understand it, is all)

im having a really hard time figuring out if there is a second ported vacuum on my carb
its a proform 750, so basically a holley

it allready has the distributor hooked up to ported vacuum, and that line is T-ed of into the vapor canister purge valve
so i dont know if id want to T the regulator into that as well


i think im gonna swap out the regulator for the old dead head style and see what that does

if nothing else, it will tell me it is or isnt the related to the regulator
 
Don’t worry too much about it. Leave the port open to atmosphere, set the fuel pressure and run it. K.I.S.S. It not need be overly complicated. And I wouldn’t choose the deadhead style over what you have. Other than for testing of course.
 
TT5.9mag said:
Don’t worry too much about it. Leave the port open to atmosphere, set the fuel pressure and run it. K.I.S.S. It not need be overly complicated. And I wouldn’t choose the deadhead style over what you have. Other than for testing of course.
Click to expand...
Well, I had it set for 6
Got on it and it dropped to 2, so something ain't right

I agree the return style should be better, that's why I swapped out the deadhead in the first place..
But it seems like a good way to troubleshoot it now
 
mopowers said:
Are the sending unit and gauge both good?
Click to expand...

The sending unit is new, and really, just a tube to suck fuel through

The gauge is not, but correspondes quite well with the mechanical gauge under the hood
 
diymirage said:
The sending unit is new, and really, just a tube to suck fuel through

The gauge is not, but correspondes quite well with the mechanical gauge under the hood
Click to expand...

I meant the electrical sending unit for the electric pressure gauge. But you said the mechanical gauge reads the same as the electric one in the car?

I'd maybe bypass the regulator all together if you have the fittings to try it out.
 
mopowers said:
I meant the electrical sending unit for the electric pressure gauge. But you said the mechanical gauge reads the same as the electric one in the car?

I'd maybe bypass the regulator all together if you have the fittings to try it out.
Click to expand...
Gotcha, yes it reads consistently a few pounds higher then the mechanical gaugs, but that one is mounted on the fuel log, while the regulator (which houses the sending unit) is mounted on the fender


I did extend the harness a foot or two myself, if that matters

I do think I will swap in the deadhead, just to see what happens

But, I forgot the duster is going in for an alignment tomorrow, so we'll do that first
 
The vacuum port will increase fuel pressure when you get on it.
And back off it should go back to set pressure.
If it works like efi regulators.
From what you are describing its a delivery issue. Inspect the rubber hoses,connection at tank, perhaps the hose is collapsing.
 
Ricks70Duster340 said:
What I said in post #7
Click to expand...
Right you are
But to be honest, I'd forgotten I have the deadhead still, and I know the pump puts out more pressure unregulated then the floats can handle

And that's just a whole nother can of worms

BUT I will swap out the regulator once I get the alignment done, and report back


@Tooljunkie
When I redid the fuel lines I made sure the "jumper" between the sending unit and the hardline was as short as possible, and lined up straight, so there is very little chance of it collapsing under throttle

But I'll look into it
 
diymirage said:
this is just not jiving in my mind
right now, pressure is dropping, so im gonna hook it up to vacuum to drop it even more?

(not that i am opposed to trying it, i just dont understand it, is all)

im having a really hard time figuring out if there is a second ported vacuum on my carb
its a proform 750, so basically a holley

it allready has the distributor hooked up to ported vacuum, and that line is T-ed of into the vapor canister purge valve
so i dont know if id want to T the regulator into that as well


i think im gonna swap out the regulator for the old dead head style and see what that does

if nothing else, it will tell me it is or isnt the related to the regulator
Click to expand...


I meant when you get the pressure drop sorted out. Then you can get a slight pressure drop at a cruise. You’d be surprised what a 1 pound decrease in fuel pressure can do for fuel mileage.
 
If you had it set at 6 and it dropped when you got on it, the pump output is low. Either the pump is going south or there is a restriction in the suction side somewhere. Might be time to do as AJ said and do a pump output test.
 
TT5.9mag said:
If you had it set at 6 and it dropped when you got on it, the pump output is low. Either the pump is going south or there is a restriction in the suction side somewhere. Might be time to do as AJ said and do a pump output test.
Click to expand...
I just dropped it off at the alignment shop, about a 20 minute drive
And it did fine (but the wife was behind me in the charger, so I didn't get on it since I didn't want to loose her)


I did get one more idea on the way over, so I'll check that out and I'll let allayall know
 
diymirage said:
Right you are
But to be honest, I'd forgotten I have the deadhead still, and I know the pump puts out more pressure unregulated then the floats can handle

And that's just a whole nother can of worms

BUT I will swap out the regulator once I get the alignment done, and report back


@Tooljunkie
When I redid the fuel lines I made sure the "jumper" between the sending unit and the hardline was as short as possible, and lined up straight, so there is very little chance of it collapsing under throttle

But I'll look into it
Click to expand...

How do you know? Have you had the gauge on it unregulated?
 
RustyRatRod said:
How do you know? Have you had the gauge on it unregulated?
Click to expand...
Now that I think about it, I don't "know"

I was referring back to an incident where it left me stranded once and when I pulled the aircleaner off it was dribbling fuel down the carb
But now that I think about it, that was after I redid the fuel system and some dirt made it past the filter and into to needle seats

Now, I do know I can adjust the pressure up to 10 PSI (and perhaps more, I haven't tried) and with this being a holley, I thought 8 was the most the floats could withstand

But no, I don't have experiential knowledge of this, since I've always had a regulator installed with this pump
 
Well, from carters website;
CDE52135-C618-48FF-B154-7CCF037638CD.png

So 8psi is all you’re supposed to get
 
On summits website they list in the description of the carter m6270 that it will flow 120 gpm from 6.9-9.5psi.
 
I have to say, if that's "ALL" the filter you have.....just that little screen, that's sorely insufficient. A five dollar wix metal filter is far superior to "that thing". I just bet you've got some small debris in that carburetor.
 
RustyRatRod said:
I have to say, if that's "ALL" the filter you have.....just that little screen, that's sorely insufficient. A five dollar wix metal filter is far superior to "that thing". I just bet you've got some small debris in that carburetor.
Click to expand...

a bigger filter is definitely on the list



on a side note, i picked her up from the alignment shop (it needs two new lower ball joints before it can he aligned) and since i was out and about i added 7 gallons of fuel to the tank (just enough to get the needle to 1/4 tank)

traffic was pretty busy so i could only get on it twice (and not able to wind it out very far) but it doesnt seem to drop in pressure now that there is gas in the tank

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