1973 Chevy Malibu Difficult - hard starting

Hi ILWeekendMechanic. Welcome to the forum. First, before you touch anything else, and when the engine is cold and about to cause this problem, peek down the carb and see if you're getting the priming squirt when you move the throttle by hand. If not, the fuel is leaving the float bowl. It is either draining back through the inlet line, (very unlikely), or it is evaporating due to excessive heat or a lead plug in the base of the carburetor is leaking. To prove evaporation is the problem, once the engine is started, let it run for just half a minute, shut it off, and let it sit overnight. If it starts instantly a day later, the fuel is evaporating. I have a Volare I bought new that has always had a long crank time except when I do that. If I run it for a minute to move it around the yard, it will start instantly weeks later.

If that doesn't help, and if you are getting a nice priming squirt, suspect a spark that is too weak to ignite gasoline but strong enough to ignite starting fluid. Your ignition coil is designed to run on around 9 - 10 volts because that's all that is available from the battery during cranking. To prevent overheating coils and points, a dropping resistor is used while the engine is running. That resistor would cause the coil voltage to be too low during cranking so it is bypassed during that time. Chrysler always did that with a separate terminal on the ignition switch, but GM used a "relay" terminal on the starter solenoid. If a starter is used without that terminal or if the wire is just left off, the spark will be real weak during cranking.

Caradiodoc

I'm confident the coil is fine based on how well the engine runs. What's at issue is the voltage that powers it. I think you're going to have to find an old-style pointer-type voltmeter. When the points are closed, current will flow through the dropping resistor, coil primary, and points to ground. Some voltage will be dropped across the resistor, so you will see around 9-10 volts on the coil's positive terminal. The dropping resistor limits current to reduce arcing points contacts. When the points are open, no current flows in the circuit and no voltage is dropped across the resistor, so you will read full system voltage on the coil's positive terminal. Voltage on the coil's positive terminal will bounce between, lets say 10 volts, (points closed), and, ... Oh, ... 14 volts when the generator is operating. A digital voltmeter snaps a reading, analyzes it, then displays it and starts over again. Those snapshots will bounce between the two voltages and be impossible to read. A pointer-type voltmeter will be unable to bounce around that fast so it tends to smooth out the reading.

Here's a couple of things you might try. Turn on the ignition switch, engine off, and measure the voltage on the coil positive terminal. (These things CAN be done with a digital voltmeter). If it reads full battery voltage, turn the engine by hand or bump the starter until the voltage goes down. When the points close, voltage on the coil will go to around 9 or 10 volts. Remember that value. That is the normal operating voltage and will be close to the battery's voltage during cranking.

Next, use a jumper wire to ground the negative coil terminal. That will keep the engine from starting. Now measure the coil's positive voltage again while cranking the engine. It must be near the voltage you found in the last step. The dropping resistor lowers voltage at the coil by a few volts. The battery voltage also drops a few volts during cranking. If you START with only 10 battery volts, then drop some more across the resistor, there will only be around 6 volts running the coil during cranking. That will result in a really weak spark, possibly not even strong enough to jump the gap in the spark plugs.

The purpose of bypassing the dropping resistor during cranking is to get the coil voltage back up to its regular operating voltage of about 10 volts. During cranking, the starter solenoid applies direct battery voltage to the coil, bypassing the dropping resistor. It does that by switching on the "relay" terminal on the solenoid. If you don't see full battery voltage on the coil positive during cranking, suspect a problem in that bypass circuit.

If that appears to be the case, run a wire directly from the battery positive terminal to the coil positive terminal, then see if it starts. (Remove that grounding wire from the coil negative). If it does, that bypass circuit is the place to look. Don't run the engine with that wire too long. The excessive curent will overheat the coil and burn the points.

Caradiodoc

Awesome, Good luck, let us know what you find.

I'm fairly confident you found the problem in the squirt, or lack of it. There are two possibilities. The accelerator pump is worn out or dried out from sitting, or the fuel is leaving the float bowl. I suspect it is fuel leaving the float bowl for a couple of reaons.

When you open the throttle, air, being light, speeds up instantly. Fuel, being heavy, takes a while to build up momentum. Until that happens, there is a severe lean spot that causes the engine to fall on its face, hesitate, stumble, even stall. The accelerator pump overcomes that by forcing the necessary fuel into the air stream under pressure. That's the squirt you should see. It is the same squirt that provides the priming pulse for the engine to start. You are seeing a very weak squirt resulting in not enough fuel to start. If that was caused by a weak acclerator pump, you would also be complaining of a severe hesitation on acceleration. Since the engine runs fine once it's running, I think the accelerator pump is ok. It has to be running out of fuel to pump.

If I'm right, what you should find is you can crank the engine for about five, maybe ten seconds to fill the float bowl, then pump the gas pedal a couple of times and the engine will start. If that works, look for a large rubber hose going from the float bowl to the charcoal canister. Pinch that hose off after running the engine. If it starts easily the next morning, fuel is vaporizing out of the float bowl and going into the charcoal canister. Another clue is if you run the engine for less than a minute, then let it sit overnight after it never got warmed up. If it starts the next morning, the fuel was not hot enough to vaporize so it stayed in the float bowl.

If there is no stumbling or hesitation on acceleration, when you stop the engine, look down the throttle bores and see what the squirts look like when you open the throttle. You should see two nice strong streams of fuel, not just a little dribble.

Caradiodoc

The float adjustment is done inside by bending a tab on the float assembly. I don't think it's off because it would also cause a hesitation upon acceleration and low power from running lean.

The next thing you might look at is to remove the cover of the carburetor after the engine has been run a few minutes, (but not excessively hot yet), and see how high the fuel level is. Put the cover back on, let it sit overnight, then check it again in the morning or after the engine is fully warmed up, and then it sits overnight. The goal is to see if the fuel level drops when it won't start. Some models have a round cover, about the size of a nickel, over the accelerator pump rod. You might be able to just lift it up and see the fuel level that way without having to take the entire cover off.

If the fuel level drops, it is going into the charcoal canister, leaking through a lead plug in the base of the carburetor, or boiling from engine heat.

Caradiodoc