I have a 454 in my '69 coupe with Edelbrock heads/intake and a 750 Quadrajet. This combination starts great, idles well and cruises well at light throttle. It also does a great job of putting out scary power when opened up in 1st and 2nd gear for a very brief period of time in my local neighborhood with 25 to 35 MPH speed limits. I recently had the occasion to enter an on ramp to the interstate where I did a more extended pull in 3rd gear. It pulled hard right up to about 70 MPH, then fell flat on it's face. I let off the throttle and it was still running just fine after dropping it into 4th and cruising. It was obvious to me that it ran out of gas as soon as it emptied the float bowl and the fuel pump couldn't keep up. It is a NEW, mechanical pump. I measured fuel flow when cranking it over on the starter at about 200 RPM at 18.6 ounces per minute. Ratio this up to 4,000 RPM and it is about 2.9 GPM or 174 GPH, at zero pressure. It seems to be a lot, but clearly is not enough for this engine and would certainly be less with back pressure against the float/ needle valve. Now for a few questions:

1. Do these numbers look good or bad to you forum readers?
2. If I abandon the mechanical pump for a Holley red electric pump, will that be enough?
3. Does the Holley pump need to mounted in the rear of the car or can it go on the frame rail near the current pump?
4. I've read that it is not a bad idea to use a return line for the excess fuel even though it is rated to work dead headed. Does this pump have a port for connecting a return line? I can't determine that from reading Holley's description of the pump or looking at pictures.

Thanks in advance for the helpful advice that I'm sure will be forthcoming.

 

Electric fuel pumps are pushers NOT pullers. They should be mounted intank for best performance. No OEM runs a external electric pump. if you must, it should be mounted below the tank. it will die very quickly if you mount it at the front of the car.
Brass tacks. LOTS of 454's on the planet run a mechanical pump. No need to go electric. your method is flawed as per checking it. You need a pressure guage.
Most likely your jetting is way off or your secondaries are way off, or anyone of a number of other issues. Just assuming that your carb is running out of fuel without checking things further sounds like a real waste of time and money. Not to mention that you will still have the problem as well as all the issues of regulating a electric pump.
Don't spin your wheels, Don't guess. check it out properly.

 

pretty sure book spec (at least on a 79) is one pint in 30 seconds..you seem to be flowing half that?
7-8.5 psi

 

The 1st thing to do is check your filter(s).
Also a q jet has a internal "filler"??? plastic block that limits fuel capacity. It can be sawed to be thinner.

 

The first thing I would check is if the carb's secondaries are even opening. To check that, the carb needs to be warmed up so that the choke is full OFF. (Don't mess with the choke at this time; just make sure it is sufficiently warmed up.) Remove air cleaner so you can clearly see all choke and carb behavior. Have someone sit in the driver's seat and [at your command] depress the accel pedal to the floor and hold it. If all is working as it should, the secondary throttle plates (in base plate of carb, so you will need to manually open the upper air valve to look into the venturi) should be nearly vertical. If they are, you have a fuel supply problem somewhere. If they are not open at all, the choke is likely still retaining the secondary lockout lever. Choke mechanism needs to be studied and corrected so that the lockout level is released when carb is warmed up.

 

I recently went through the carb with some expert help. I have a good friend from high school who recently retired from GM and spent the first part of his career at Rochester Products division doing telephone support for carburetor problems. With his guidance, I rejetted the carb with 1970 corvette spec jets and rods, and put in a new needle valve under the float. I have a manual choke installed so when I push it all the way in the choke is off and there is no chance that the choke is preventing the secondaries from opening. I know that they were open because there is a dramatic change in sound and power when Qjet secondaries open and it pulled hard, for a couple seconds, then completely died. That sure sounds to me like fuel starvation and not lack of secondaries or a jetting issue. I also run an inline fuel filter with a glass housing and the filter housing at the carb is empty so it's not that.

I have a pressure gage and will rig up a T connection so I can see what it shows while running. I could just have a weak fuel pump from O'Reilly's too.

Thank you for the guidance on using an electric pump and I will rear mount it if I go that way. I agree that thousands of big blocks run well with a stock mechanical pump and the fact that I have a new one has me perplexed. More testing to come and eventually I should figure this out!

 

It is possible you just got a bad one. frustrating, but possible. also possible there is a restriction somewhere.

 

Definitely sounds like a fuel starvation problem caused by the fuel pump, fuel filter, fuel lines or carb float level. Or possibly a gas tank venting issue.

 

Try a carter pump no need for anything real crazy. Ill take a mech fuel pump all day over the buzzing over an electric and worrying about that going out too. Put a gauge on it to get your fuel pressure dialed in right. Edelbrocks and Holleys use two different psi

 

I checked out the carter pump but I didn't like the 1/4 NPT threaded connections since the fuel line is 3/8. I ordered a holley made 110 GPH mechanical pump with 3/8 NPT ports. I will repost the results here when I get it installed and test it on the road.

 

Check your float level......and see if you have the filter in the Q-Jet with or without the check valve......the filter with check valve is not recommended for over 400hp as it restricts fuel flow a bit.....
L-88's ran mechanical pumps with no issues and you can too......but you may need much more with the heads and other mods......the Q-Jet should support it but only if the float level is right and it is getting enough volume in the bowl. Float level on a Q-Jet is a small PITA.....but a necessary one, as I have seen MANY that are too low. The good news is that you can do these two things up top for about $10.

Jebby

 

After installing the new Holley 110 GPH mechanical pump, I took the car to a nearby highway on ramp where I could stand on it for more than 2 seconds without going to jail and it ran fine up to about 70 in third gear, at which point I had to back off or hit the guy in front of me. After slowing down to 60 and letting some traffic clear, I floored it in 4th gear and let it run from 60 to 90 and it never coughed once. It was the Chinese pump from O'Reilly's and the new holley fixed it. Thanks to everyone who posted in response to me issue.

Paul

 

Hello Paul71LT1!

I have had the same problems with pumps not keeping up with my 427's thirst for good fuel and LOTS of it! The very first time I went drag racing I kept having to raise the floats a bit more so I had fuel all the way to the end. I did a lot of 13.05 runs to keep from being taken off the track. My tires would spin past the 1/8th mile point on the quarter mile track. Traction is the problem on my Corvette. I tried a pair DOT Drag Radials and promptly blew a half shaft apart.

I recently switched over my 1968 to a Holley Sniper Stealth unit and I was expecting to/planning on Buying a new fuel tank. When I spoke to the shop who sold me the system they told me about the new Holley Fuel Tank Modules and how they use the factory tank. I bought one and it took about 20 minutes to install a the 1968 has the opening on the bottom of the fuel tank. Now I have 58 p.s.i. at my throttle body and you hear very little as the pump and regulator are INSIDE the fuel tank. This means No return lines either and the pump is a Walbro unit like the ones that come on the C4's. I am sure you can regulate it down inside the tank to 6 psi and go for broke.

I used to play with my Corvette out on a Runway at a local small airport where I kept my Cessna. It was 2600-2800 feet long and I could easily hit the 130 mark before having to slow down. I would put the tail over the end of the runway and just go for it. It was fun as they had 100 octane Fuel available for less than a $1 over regular car gasoline. Unfortunately it developed lead buildups on my plugs and valves inside the combustion chamber. The other problem is that 1968 C3's try to "take off" the faster you go, the front end starts getting light at over 130 mph. (Not that I do 130 very often anymore.) I only do stuff like this in places where it is safe for the people around me, I try not to be reckless on the highways. It is one thing to kill myself doing something stupid but I won't hurt others ever.

With 12.25-1 Compression I am in the 11 second range IF i installed a roll cage to find out. On a On-Ramp to I-95 I could easily hit 105-110 mph before merging into traffic. The electric fuel pump makes such a difference in a constant fuel supply for me. The shop I dealt with is called EFISYSTEMPRO and they are online. They have the best service you could ask for in setting up a new EFI system.

There is a device called a GTECH Pro that will help you get your Corvette running the best it can. You enter the (accurate) weight of the Corvette with you and a tank of gas. Then you put it on the dashboard and it measures the speed and calculates the Horsepower and torque of your engine. I would adjust the car or make a change and then go to an empty Parking lot and plot some 30-60 mph times to see if there was any improvement. They make phone apps that can do this but are nowhere as accurate as the GTECH is. Mine even has shift lights on it, it watches the Torque and tells you to shift at the optimum points to get the best time. It is a handy device when you like to tinker on your Corvette.

 

Paul
Can you tell me how you clocked the holley fuel pump? what fittings did you use to get the fuel lines to fit
I have a 383 and cant figure out how to route line. Any pictures would help greatly.

 

Yes I would love to see some pics as well…
I have a Edelbrock 110 GPH but even clocking it there is simply no room in there for it.
The pump is just way too big to even put any fittings not hitting the frame.

Now I purchased a Holley 80 GPH and it’s much smaller, but I still had to clock it in order to give fittings as much space as possible