Since sparking the life back into the 73, I've had two major problems, rough idle and surge.

Replaced the fuel pump and had the Q-jet rebuilt, then replaced plugs, wires, condenser, rotor and cap.

To fix the rough idle, plugged every vacuum line and the EGR, but no improvement. Thought maybe the rpm picked up after spraying starter fluid near the right rear of the intake manifold, and decided to replace the gasket.

While removing the intake manifold, noticed that my carburetor gasket had covered a V-shaped grove on the manifold, which appeared to line up with a small port on the bottom of the Q-jet (and I’m thinking this small port is for the idle vacuum). Although it appeared that the rough idle mystery was solved, the stock intake manifold was major heavy and damn ugly, so I replaced it with an Edlebrock Performer (no EGR thank you). After startup and setting timing, the idle is much smoother.

Onward to the next problem. If no load on the engine, there is no surge problem. In other words, I can sit in the driveway and rev the engine with no apparent problems. When driving the car, soon as I get into the throttle, the engine picks up for a few seconds, then dies down, almost to a stall, like it’s starved for gas. If I ease off on the throttle, the engine comes back, and, by slowly giving it throttle, can get up to speed. The problem is worse on any hill (more load?). Note, doesn’t appear to be a transmission downshift problem. Modulator was replaced, and the problem doesn’t resolve if I manually downshift.

As previously noted, the fuel pump is new. But, the car sat in my neighbor’s garage with no use for 11 years. When purchased, the gas tank was full, so all the old gas was siphoned out. Was, and still am, concerned for the condition of the gas tank, so installed a glass in-line filter in front of the carburetor (outlet side of the fuel pump), and have observed small black particulates (relatively few in number-not enough to clog the filter), but no signs of rust.

One thing which seems unusual is that the fuel filter empties itself of gas (drains back through the fuel pump) after engine shut down. Is there a check valve in the fuel pump to prevent backflow? Maybe the check valve is clogged with the small black particulates? Maybe I should have put another filter on the inlet side of the pump? HELP IS NEEDED FROM YOU FUEL PUMP EXPERTS!

Every book I read tells me that when you suspect the fuel pump, this usually isn’t the problem, and that ignition should be suspected. Since my problem is only under load, does this rule out ignition failure? If ignition failure, which component could cause the surge problem?

Other causes for the surge problem. Could it be: a carburetor problem causing low volume of gas available in the float chamber? Clogged inlet in the gas tank? Other ideas most welcome, and please include any advice on diagnostics. Simple language is best, as I’m just a backyard kind of mechanic.

 

Since nobody has responded thought that I'd take a shot at one of your problems. Because you indicate fuel flowing back into the tank after the engine is shut down, I'm guessing that the air port in your gas tank cap is plugged. When the engine is running, the fuel pump is creating a vacuum and the vacuum is retricting the amount of fuel to the carb.

 

Hey, thanks for the reply. Will loosen the cap and see what happens. Easy enough.

Another thought. What about a possible restriction to fuel flow into the Q-jet (after the filter, but before the needle valve and float chamber), such as a piece of pastic or other gunk. Could I observe a possible obstruction just by removing the filter and looking inside, or is a tear down necessary.

 

Sounds like a buggered-up fuel filter to me. (Well, it sounds like a plausible place to start diagnosing.) Take it completely out of the carb (for diagnostic purposes only) and run it around the block and see what happens. Then THROW IT THE F*** AWAY if it's one of those cheapo crapo filters in the inlet and install an in-line filter.

 

Another possibility would be a plugged fuel tank strainer. This is a sock-type filter that is inside the tank. I get the impression the car has been sitting so there may be rust in the tank that plugged the strainer. The strainer can be replaced without removing the tank, BTW, so is not a big deal.

 

I like the strainer idea. Easy and cheap (thinking about it, but won't make a cheesy comment regarding my wife).

For the paper fuel filter in the carb, agree, could easily give the cheap thing a toss, but don't think this is the problem, as already checked if out and also have an in-line filter.

Thanks for the thoughts.

Any more ideas?