Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

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flathead31coupe said:
I knew that I read that in your last post. I was wondering should I come from up front on my regulator by the carburetors or block that one and use the return at the pump?
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I was just wondering and where can you go with a return on a factory tank? I don't have any more room on my sending unit to make it any bigger if I need to . Someone said you can go into the filler neck but I don't know
 
flathead31coupe said:
I was just wondering and where can you go with a return on a factory tank? I don't have any more room on my sending unit to make it any bigger if I need to . Someone said you can go into the filler neck but I don't know
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I weld a fitting in the upper corner on the passenger side of the tank.
 
flathead31coupe said:
Cool thanks.... What about the return? Should I take it from the front if need be and run it all the way back or plug it at the regulator and use the return on the fuel pump?
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I prefer to run a separate return line and not use the bypass at the pump. It’s more work to do it that way, but IMO you want the pressure drop at the regulator and not the pump.
 
Rat Bastid said:
I prefer to run a separate return line and not use the bypass at the pump. It’s more work to do it that way, but IMO you want the pressure drop at the regulator and not the pump.
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Ok thanks, I found this looks like it would make a return line easy without dropping the tank. Some say you need it close to the bottom but away from the sending unit. Other say on top opposite of the sending unit or supply. My current return is in my sending unit going straight back into the tank but I cannot make it any bigger so alternate location would be needed if I need it

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flathead31coupe said:
Ok thanks, I found this looks like it would make a return line easy without dropping the tank. Some say you need it close to the bottom but away from the sending unit. Other say on top opposite of the sending unit or supply. My current return is in my sending unit going straight back into the tank but I cannot make it any bigger so alternate location would be needed if I need it

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Thats a -6 AN. If your return line is -8, I would want that fitting to be -8 too.

There are other styles of bulkhead fittings if you dont want to weld a fitting on the tank that may work better.

The thing about bulkhead fittings is you have to be able to get to the backside of the fitting, which means you have to get your hand and a wrench in the tank. If you can do that than a bulkhead fitting is the easiest, best way to do it.

As to where it goes, there is a whole bunch of nonsense out there about that. Try and avoid blowing the fuel right on top of the pickup. That’s about it.

If you mount it say, 3-4 inches on either side of the OE pick up, you’ll be fine. It will put the fuel back in the tank far enough away from the pick up that it won’t matter.
 
flathead31coupe said:
Well, it turns out that the Mallory fuel pump I bought was a 5250. It's a series 250, not 240. Let's hope it's not too big lol
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Dang. That’s a good deal for that pump. As long as your regulator can bypass enough fuel you’ll be pooping in tall cotton. Nice score.
 
How much lift can one of those pumps handle are all of them about the same? They are better at pulling then pushing because if it would work I would like to run my supply line up and around like it was originally. So it's out away from the rear end and everything. But if it's not going to work I'll leave it like it is
 
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Well, it looks like it's turning out that I don't have enough volume to run. The pressure is good but the volume will not handle. The two four barrels is what somebody's telling me. The 3/8 line and 3/8 return does not handle enough volume to keep the float bowls full. It's got plenty of pressure but not enough volume. Thoughts?
 
You could put 8 four barrels on there and a 3/8 feed would still be enough if you have the pump, lines, tank and all associated parts plumbed correctly. It’s not how many carburetors you have. You aren't making enough hp to need more than a 3/8 line. We’ve told you how to fix it, stop micky mousing stuff and do it right.
 
TT5.9mag said:
You could put 8 four barrels on there and a 3/8 feed would still be enough if you have the pump, lines, tank and all associated parts plumbed correctly. It’s not how many carburetors you have. You aren't making enough hp to need more than a 3/8 line. We’ve told you how to fix it, stop micky mousing stuff and do it right.
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I receive my Mallory 250 today. We will see what happens.
 
I looked for details on the Mallory 250 and came up with an instruction sheet. It does not say if it will pull fuel, but it doesn’t say it won’t either.
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I’m sure someone somewhere has done some testing on it but a quick google search didn’t turn up what I was looking for. @Rat Bastid i know you’ve used those, have you done any testing on them to see if they’ll pull fuel?
 
Thanks for all the info. I've been over a lot with the guys here and realize that the holley pumps do push better than pull. By me, eliminating the bypass and putting a gauge before the regulator has determined that both pumps are not putting out enough pressure . Even the one that I replaced the spring that should have boosted the pressure to 19 only went to 10 to me. That lets me know that those pumps are not working right. I will see what the Mallory 250 will do
 
TT5.9mag said:
I looked for details on the Mallory 250 and came up with an instruction sheet. It does not say if it will pull fuel, but it doesn’t say it won’t either.
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I’m sure someone somewhere has done some testing on it but a quick google search didn’t turn up what I was looking for. @Rat Bastid i know you’ve used those, have you done any testing on them to see if they’ll pull fuel?
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They will pull 3 feet but you go over that and they start losing output.
 
Yes, but what you are interested in though, is the flow rate of whatever pump you are using AT the pressure you will be using it at, including whatever restriction is in the system. So I’d set up a flow test through all of your lines and regulator, without the carbs at the end, into a bucket with the reg set at your desired pressure.
 
TT5.9mag said:
Yes, but what you are interested in though, is the flow rate of whatever pump you are using AT the pressure you will be using it at, including whatever restriction is in the system. So I’d set up a flow test through all of your lines and regulator, without the carbs at the end, into a bucket with the reg set at your desired pressure.
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Ok thanks... I'm still getting ready to put that Mallory 250 in place of the holly blue fuel pumps. Unless there is a restriction somewhere that I don't know about by blocking off the return line from the regulator and putting a gauge on the inlet side of the regulator from the pump that should have showed me the full pressure of what pump I am using. I'm assuming it should be at least 14 PSI is what Holly said and by me putting the other spring in should have made it 19 PSI. It only went to 11 and took a while to get there. But I've already covered this. So I guess I'm kicking a dead horse and will try the Mallory 250
 
Just an update. Haven't worked with the Mallory fuel pump yet, but the fuel pump in question the new Holly blue. I hooked it back up with the filters to my existing lines and ran it from the regulator to a gas can and it barely trickled out so.... Along with deadhead the regulator and it not making very much pressure. It definitely don't have enough flow. So as soon as I can I'll try the Mallory out. Hopefully that'll fix it
 
flathead31coupe said:
Just an update. Haven't worked with the Mallory fuel pump yet, but the fuel pump in question the new Holly blue. I hooked it back up with the filters to my existing lines and ran it from the regulator to a gas can and it barely trickled out so.... Along with deadhead the regulator and it not making very much pressure. It definitely don't have enough flow. So as soon as I can I'll try the Mallory out. Hopefully that'll fix it
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Remove the regulator and do the same test.
 
flathead31coupe said:
I did that. There's no change in flow. It was real weak after the regulator and before the regulator
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flathead31coupe said:
I did that. There's no change in flow. It was real weak after the regulator and before the regulator
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flathead31coupe said:
I did that. There's no change in flow. It was real weak after the regulator and before the regulator
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flathead31coupe said:
I did that. There's no change in flow. It was real weak after the regulator and before the regulator
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flathead31coupe said:
I did that. There's no change in flow. It was real weak after the regulator and before the regulator
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So is that a pretty good sign at that pump is bad
 
It’s a sign that the volume is not adequate before the regulator, that’s all. The pump may be good and it’s supply is insufficient, or a filter clogged, or a pickup screen clogged, or the pump won’t pull fuel how you have it set up, or the pump is bad. All possibilities
 
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