Engine began to surge and cutout at WOT so I taped a fuel pressure gauge to the windshield to check for pressure drop. If I nail it, the pressure drops below 1psi and that's only at 4500-5000rpm! I'm running a mechanical Carter Strip pump (part # M4891 I believe) with a Holley regulator and an Edelbrock carb. 5/16" line coming from the tank and 3/8" line from pump to carb. At idle I get 5.25psi.

I used the same pump and regulator on a mid-12sec car with no issues.

At most the engine is making ~350hp at my altitude so it shouldn't need a whole lot of volume. The only things I imagine it could be are:

1) Dirty filter
2) Maybe the 4' hose running from the 'T' in the fuel line to the gauge taped to the window is showing excessive pressure drop.

Any ideas guys?

I taped a fuel pressure gauge to the windshield to check for pressure drop

Good man. You're doing it the right way. The long hose won't cause that kind of pressure drop. I use a 6' line to feed my remote mount fuel pressure gague and it causes no inaccurate readings.

Some cars just do stuff like this. I don't know why or how, but the long draw from the tank is just too much sometimes. I've owned several 78-87 G-bodies and they all had problems when only using a block-mounted mechanical. And I'm talking about when only running low 14s- not exactly rocketship fast times!

Obviously, check the fuel filter- that's an obvious point of restriction if it's dirty, but don't assume that must be it.

Go through the whole system from the tank pickup (maybe the stock in-tank "sock" is collapsed or clogged up with dirt/rust) all the way up the lines looking for kinks, obstructions, etc. At the end of the day, I found that there are some cars, like my Malibus, that just can't get it done with a mechanical alone no matter what I do with the lines. That's when the electrical "helper" pump gets installed back near the tank (Holley Red or Carter 5 PSI street pump). And then I have no more issues.

BTW- if you get the chance, pick up a typical 20' coil of 3/8" fuel line at the local speed shop and try to blow through it. You'll be amazed how difficult it is (vs., say, a one foot length). THink about your pump having to do the same work while feeding enough fuel to feed a V8.

Thanks for the info Damon. I think I have a Holley Red hanging around here somewhere. I'll throw that in and see if it helps. I tried cleaning the filter (sintered bronze Summit unit) but the same thing happens. I'll try pulling the filter out completely and see if the sintered bronze is still clogged up.

Sound like I'll probably have to drop the tank and see if there is an obstruction or if it isn't venting properly.

It also appears that my 5/16" fuel line is too small. After searching around it looks like 5/16" supports ~300hp. Guess it's time for a fuel line upgrade. :(

elfear... Sounds like your not moving enough fuel.. You pretty much have it figured out.. My money would be on the 5/16" line is too small to flow the vol. of fuel thats needed.

IMO 3/8" from in the tank to the carb is the smallest to ever run on any "performance" engine

elfear... Sounds like your not moving enough fuel.. You pretty much have it figured out.. My money would be on the 5/16" line is too small to flow the vol. of fuel thats needed.

IMO 3/8" from in the tank to the carb is the smallest to ever run on any "performance" engine

Ya, I should have thought about that before I got everything put together. I think I'll run some 1/2" aluminum fuel line from the tank to the pump just to be safe. I know that's overkill but if I step up the hp level one day I'll be glad I don't have to upgrade the fuel line as well.

How would you guys connect the 1/2" line to the fuel pump, which I believe has 1/4" NPT fittings?

Now you do know, you'll have to pull the sender/pickup out of the tank to do this fully.

The 5/16" line just don't start/stop at the top of tank. That same supply line goes through top of pickup and down into tank.

No sence in going bigger on all the line under the car, if you don't take care of whats at and in the tank..

When we do it, we remove the pickup from tank, cut supply line off at bottom of the part part of pickup, then drill the hole out in pick up to fit the line size it's been upgraded with.. Run the new line through pickup to the right depth, and solder/braze the line to top of pickup... A few buddies of mine has installed the new line with JB weld.. It's worked for them but myself I don't think I would take the route unless it was a have to type of thing.

as far as the pump fitting, you can buy adapters to adapt just about any size combo together

Now you do know, you'll have to pull the sender/pickup out of the tank to do this fully.

The 5/16" line just don't start/stop at the top of tank. That same supply line goes through top of pickup and down into tank.

No sence in going bigger on all the line under the car, if you don't take care of whats at and in the tank..

When we do it, we remove the pickup from tank, cut supply line off at bottom of the part part of pickup, then drill the hole out in pick up to fit the line size it's been upgraded with.. Run the new line through pickup to the right depth, and solder/braze the line to top of pickup... A few buddies of mine has installed the new line with JB weld.. It's worked for them but myself I don't think I would take the route unless it was a have to type of thing.

as far as the pump fitting, you can buy adapters to adapt just about any size combo together

I've been thinking about how I want to upgrade the portion of the line that goes into the tank. I was thinking JB Weld but maybe I'll get it soldered if that's better, although I don't think solder will stick to aluminum tubing so I may be stuck using JB Weld. The bend coming out of the top of the tank is also going to be exciting. Seems like there's such a narrow gap between the tank and the body of the car that you either have to bend the line at a 45-90 degree angle or seal the pickup tube in at an angle. I'll probbaly try the latter so there isn't as much restriction.

I'll look around for the right fittings but I remember when I was doing this same thing for my Camaro I couldn't ever find anything that did a simple conversion from 1/2" to 1/4" NPT.

Oh we know there is a simple solution,, but it takes up so much trunk space ;) :) ;) :)

Oh we know there is a simple solution,, but it takes up so much trunk space ;) :) ;) :)

Ya I thought about that but this is still my family sedan. I guess realistically we'll probably never take it on trips so maybe the trunk space isn't so important after all.....

Running a Holley red back by the tank with a Carter 6 PSI mechanical up front in my friend's 72 Chevelle. It originally came with a 307 2bbl motor so the fuel line is the smaller 5/16". The combination of the two pumps holds 6PSI through the whole run- good enough for bottom 12s. Unhook the electrical pump and it won't rev past 5000. Same deal in the 78 Malibu in my signature, below, although my Bu did come with the slightly larger 3/8" feed line from the factory.

The pusher pump at the back makes a big difference, even if the feed line is too small.

And loads easier than bending up almost 20 feet of custom line plus dropping the tank and modifying the pickup.

Running a Holley red back by the tank with a Carter 6 PSI mechanical up front in my friend's 72 Chevelle. It originally came with a 307 2bbl motor so the fuel line is the smaller 5/16". The combination of the two pumps holds 6PSI through the whole run- good enough for bottom 12s. Unhook the electrical pump and it won't rev past 5000. Same deal in the 78 Malibu in my signature, below, although my Bu did come with the slightly larger 3/8" feed line from the factory.

The pusher pump at the back makes a big difference, even if the feed line is too small.

And loads easier than bending up almost 20 feet of custom line plus dropping the tank and modifying the pickup.

Hmm. Good point. It was a royal pain to solder a a pickup tube into the tank in my Camaro and bend all that tubing. Do you think I'll be ok at sea level when the combination should be making closer to 420-430hp?

Just wanted to give you guys an update. I decided to just bite the bullet and install a 1/2" fuel line. Drilled out the 5/16" pickup tube and brazed in a copper 1/2" tube. Fuel pressure now looks a lot better at WOT but it still drops down to 2.5-3psi. I'll try bumping the fuel pressure up a bit but I'm pretty much maxed right now at 5.25psi@idle because of the Edelbrock.

Does that sound like it's dropping down too low?

Edit: Just did a more comprehensive test and it looks like it still drops down to 1psi or so. :( Is there any way the regulator could be at fault?

Possibly. I'd ditch the regulator (temporarily) and direct-connect the pump to the carb to test it. It might flood it out at idle but you don't care about that for a quick test- just keep it running and make a few WOT runs to see how the fuel pressure holds up. If it's still dropping off the same you need that "helper" pump at the back I was talking about. You can't imagine the difference it makes. On several of my cars the engine will basically "shut off" around 4500 without the helper pump doing it's thing. The Malibu in my sig, below, is one example of that.

Possibly. I'd ditch the regulator (temporarily) and direct-connect the pump to the carb to test it. It might flood it out at idle but you don't care about that for a quick test- just keep it running and make a few WOT runs to see how the fuel pressure holds up. If it's still dropping off the same you need that "helper" pump at the back I was talking about. You can't imagine the difference it makes. On several of my cars the engine will basically "shut off" around 4500 without the helper pump doing it's thing. The Malibu in my sig, below, is one example of that.

I'll give that a shot tomorrow and see what happens. Thanks for the advice.

Wow. This is a very interesting thread. I wanted to check my pressure in the same manner (just for kicks) but I'm not having any troubles up past 5000. I'm just curious on what pressure I'm getting. All I have is a Carter electric pump in the back. Seems great. But is it better to add a mecahnical pump in addition to the electric one, or just get a bigger electric one?

Okay, I finally got around to connecting the fuel pump directly to the carb. At idle I get about 8psi, which sounds normal, and at at WOT it drops to 3psi or less. Does that sound like the pump is the culprit? It's 10yrs old and it seems like it's needing to be retired.