Engine: 56 g.h. That runs fine up to 3000 rpm

[DMB-8]

This engine has been completely rebuilt and runs fine up to about 2800 rpm,then it just falls on its face.It has a new Edelbrock carb and a Delco Remy Distributor with a Petronix ignition and 40,000 volt coil.I know that it should have an Autolite dist.but this one is for a 352 Packard.
It also has an electric fuel pump which I changed to a higher delivery than the first one.I just don't know what else to check timing seems to be good and it starts and runs fine till you get on it.Any help would be appreciated.Thank You,Don Borger

[JoeHall]

Not sure what you mean by, "falls on its face", but can think of several potential problems: carb linkage interference; exhaust system plugged up; malfunction in the Delco distributor (disassemble and inspect); valves out of time, or valves seated too deep in the heads, extending the spring length when seated (makes the springs too weak to close the valves properly at higher RPM).
Good luck,
Joe H

[StudeRich]

As Joe said, shimming the Valve Springs COULD fix it but, I would think the Hydraulic Valve Lifters would be more tolerant than the Solid Lifters I am used to in Stude. Engines.

Also check for sticking Vacuum Advance or Centrifugal Advance in Dist.

Were the Valves adjusted?

[sals54]

Start with the easiest things first. Linkage. See if you're getting full throttle by sitting in the car with your gas pedal on the floor, then have someone check to see if you're at full throttle on the carb.
That is the first thing to check. And its free.
Then move to timing. Then check for fuel delivery. Check your fuel pressure at the carb while running at speed. You may be suffering from fuel starvation. See what you get from there before going into the engine.

[DMB-8]

The engine just like it is shutting down.I have changed electric fuel pumps to a higher output pump with no change.I suspect the distributor but don't know how to fix it or if it could be that.Thank You,Don

[JoeHall]

The engine just like it is shutting down.I have changed electric fuel pumps to a higher output pump with no change.I suspect the distributor but don't know how to fix it or if it could be that.Thank You,Don

Why not replace that Delco with an OEM Auto-Lite. They were designed for the 56J, and the earlier, 'C' version works best. The later version de-tuned the 56J a tad, by reducing the advance curve. Should be easy enough to find one, then may have Brent Hagen help you with rebuilding it.

If the person who rebuilt the heads did not know what he was doing, you could have a problem with springs, as I mentioned above. Easiest way to check is to measure seated valves' spring length; should be 1.8" if I recall. I am sure Jack V. will be along soon to help us all with those kinda details.

[PackardV8]

This engine has been completely rebuilt and runs fine up to about 2800 rpm,then it just falls on its face. . . . The engine just like it is shutting down.

Is the symptom load dependent? If at cruise, easing up to 2800, does it still cut out? Accelerating hard, cuts out? Does it immediately pick up when the RPM come below 2,800?

1. It's not the valve springs. Float just makes the power go soft and not at 2800 RPM.

2. It's possibly fuel, but again, starvation stutters first. Is there a fuel filter in the system? A temporary fuel pressure gauge tells all.

3. Since it's a Delco, the tach drive isn't in place is it?

4. Are the spark plugs, wires, cap, rotor, all new? If not, get back to us when they are.

jack vines

[gordr]

One off the wall idea: I have heard of cases where a loose piece of under-hood insulation obstructed the intake tube of the air filter. Make sure the engine is getting all the air it needs.

[skyway]

"One off the wall idea"
My '41 Commander did this. It came stock with the non-oil bath air filter,
which has a round pad of "horsehair" in the lid as a silencer. Under hard acceleration
that pad would get sucked down over the carb throat causing the car to fall on its face, only to come back once
you let off the accel. An oil bath filter solved it.

[TWChamp]

Two summers ago my 50 Champion throttle linkage was catching on some metal part, so it accelerated then fell flat. Had me puzzled at first, but after a few miles I pulled over and saw the problem. I needed to keep the end of the linkage further from the carb by placing a flat washer between the linkage and throttle lever.

[DMB-8]

The car has all new rotor,cap, wires,and plugs.I had an auto lite distributor but it did not work right and I purchased this Delco on the forum.I did not know it was a Delco until it arrived.I purchased a new petronix module for it and it started and ran much better until you kicked it down and it was like you turned the key off.It will do it in the shop with the air cleaner off and the linkage is not restricted.It has an after market tach but we tried disconnecting it with no change in the problem.Thank You,Don

[studegary]

Does your Hawk have an overdrive transmission? Perhaps the switch that cuts off the ignition momentarily is malfunctioning or misadjusted.

[Son O Lark]

Make sure your fuel tank cap is vented well.

[doofus]

Is your exhaust system free flowing? have you checked your ballast resistor? the resistor will break down under a hard load and be ok on light load BTDT. Luck Doofus

[Chuck Larmay]

I had somewhat the same problem with a GTO. When I gave it the full peddle it would reach a certain RPM and then start missing big time. What I found is, I didn't have a good 12 volts going to the new HEI distributor. Fix that and no more problem.