Where the choke is and what it does

The choke on a 1966 Mustang is a valve in the carburetor that restricts airflow when the engine is cold, making the fuel mixture richer so the engine will start. On most 1966 Mustangs, you'll find the choke mounted on top of or integrated into the carburetor itself, which sits on the intake manifold in the center of the engine bay. The choke is controlled by a cable that runs from the carburetor up through the firewall to a knob or lever inside the car, usually on the dashboard to the left of the steering column.

Unlike modern cars with automatic chokes, the 1966 Mustang requires manual adjustment. You pull the choke knob out when starting a cold engine, then push it back in as the engine warms up. If your choke is stuck, won't move smoothly, or isn't controlling the engine's idle properly, you'll need to adjust it at the carburetor itself.

Key Takeaways

  • The choke cable connects the dashboard knob to the carburetor valve, and you can adjust how much cable tension exists by loosening the cable clamp at the carburetor.
  • A choke that won't fully open or close usually means the cable is too tight or too loose, which you can fix by repositioning the cable in its clamp.
  • The choke butterfly valve inside the carburetor can stick from varnish buildup, and cleaning it with carburetor cleaner often restores smooth operation.
  • If the choke knob moves but the engine doesn't respond, the cable may have separated inside the firewall or the valve itself may be damaged.

Checking cable tension and adjusting the clamp

Start with the engine cold and the choke knob pushed all the way in (the off position). Look under the hood at the carburetor and locate the choke cable where it enters the carburetor housing. You'll see a small clamp or bracket holding the cable in place. Pull the choke knob out fully from inside the car and watch the carburetor — the choke butterfly valve should open noticeably. If it barely moves or doesn't move at all, the cable is too loose.

To tighten the cable, locate the bolt or screw holding the cable clamp to the carburetor. Loosen this bolt just enough that you can slide the cable slightly through the clamp. Pull the cable taut (not so hard you strain it, just until it's snug) and retighten the bolt. Test the choke knob again — it should move smoothly and the butterfly should open and close with it. If the choke now opens too much or won't close all the way, you've tightened it too far; loosen the clamp bolt again and slide the cable back slightly.

Freeing a stuck choke butterfly

If the cable moves freely but the choke butterfly inside the carburetor won't budge, the valve is likely stuck from old fuel varnish. Spray carburetor cleaner directly into the choke housing where the butterfly sits. You may need to spray several times and let the cleaner soak for a few minutes. Gently try to move the choke knob back and forth — do not force it, as you can bend the valve or break the cable.

Once the cleaner has had time to work, try the knob again. You should feel it loosen gradually. Repeat the spray-and-wait cycle until the butterfly moves freely. After it's loose, pull the choke knob in and out several times to work the cleaner through the mechanism. Start the engine and let it idle for a minute, then push the choke knob in slowly while watching the engine idle speed drop back to normal — this confirms the butterfly is opening and closing as it should.

Testing the choke after adjustment

The real test is a cold start. Let the engine sit overnight or for at least several hours so it's truly cold. Pull the choke knob all the way out, then turn the key to start. The engine should catch quickly and run at a higher idle speed (usually 1,000 to 1,200 rpm). As the engine warms up over the next minute or two, slowly push the choke knob back in. The idle speed should gradually drop back to normal (around 500 to 700 rpm). If the engine stumbles or stalls when you push the choke in, push it back out slightly and let the engine warm a bit longer before trying again.

If the engine won't start even with the choke fully out, or if it runs too lean (rough and hesitant) even after warming up, the problem may be deeper than cable adjustment — the carburetor itself may need cleaning or the choke valve may be damaged. If the choke knob moves but nothing happens at the carburetor, the cable has likely broken inside the firewall and will need to be replaced.

When to replace the cable instead of adjusting it

If the choke knob moves but feels loose or sloppy, or if it moves but the carburetor valve doesn't respond at all, the cable is probably frayed or broken inside its sheath. A broken cable cannot be adjusted — it must be replaced. To replace it, you'll need to disconnect the cable at both ends: at the dashboard knob and at the carburetor clamp. The cable runs through the firewall, so you may need to remove some dashboard trim to access the firewall connection. A new choke cable for a 1966 Mustang costs between $20 and $50 depending on the supplier.

If the cable is intact but the knob itself is cracked or won't stay in position, you can often replace just the knob without replacing the entire cable. The knob typically screws or clips onto the cable end inside the car. Check whether your knob is held by a set screw or a clip, then source a replacement knob from a Mustang parts supplier.

Preventing choke problems going forward

The most common cause of choke trouble is fuel sitting in the carburetor for weeks or months, leaving varnish that gums up the butterfly valve. If you store your Mustang for the winter or for any extended period, run the engine until it's warm, then turn it off and when ready drain the carburetor bowl by opening the drain plug at the bottom of the carburetor. This removes fuel that would otherwise oxidize and harden. Alternatively, add a fuel stabilizer to the tank before storage — this slows varnish formation.

Check the choke cable annually for fraying or corrosion, especially if your car sits outdoors. A light coat of silicone spray on the cable sheath (not on the knob itself, where it would be slippery) helps prevent rust and keeps the cable moving smoothly. If you notice the choke knob becoming harder to move, address it when ready — a tight cable can break suddenly and leave you unable to start the car in cold weather.

Frequently Asked Questions

Should the choke knob be in or out when the engine is warm?

The choke knob should be pushed all the way in when the engine is warm or running. Leaving it pulled out (on) while driving causes the engine to run too rich, wastes fuel, and fouls the spark plugs. Pull it out only when starting a cold engine, then push it back in as soon as the engine is warm enough to idle smoothly on its own.

Can I drive the car with the choke stuck in the open position?

You can drive it, but the engine will run lean and may hesitate or stall, especially at low speeds. A stuck-open choke means the engine isn't getting enough fuel when cold. It's better to fix the choke before driving, or if you must drive, let the engine warm up thoroughly before putting it in gear and drive gently until it reaches full operating temperature.

What if the choke works but the engine still won't start when cold?

The choke may be working but the carburetor itself may need cleaning, or the spark plugs may be fouled. Try replacing the spark plugs first — they're inexpensive and often the culprit. If that doesn't help, the carburetor bowl may have varnish buildup that's blocking fuel flow, which requires carburetor removal and cleaning or a professional rebuild.

Is there a way to make the choke automatic on a 1966 Mustang?

Yes, but it requires replacing the carburetor with a later model that has a built-in automatic choke, or installing an aftermarket electric choke conversion kit. Both options are more expensive than maintaining the manual choke and are usually done only during a larger carburetor rebuild or engine swap. For most owners, keeping the manual choke adjusted properly is the simpler choice.