Carburetor Cleaning: Complete Guide for Classic Cars

First, disconnect the battery. No sense risking a spark near gas fumes. Then:

1. Label and disconnect all hoses, linkages, and electrical connections. A Sharpie and masking tape are your friends here.
2. Remove the air cleaner assembly. Some cars have a wingnut or clips; others need a screwdriver.
3. Unbolt the carburetor from the intake manifold. Most use 4 bolts (5/16” or 3/8” socket). Support the carb as you remove the last bolt—it’s heavier than you think.
4. Stuff a clean rag into the intake manifold opening. Dirt falling in there is a nightmare to clean later.

Lay out a clean workspace with a parts tray or egg carton to keep screws and small parts organized. Take photos as you go—this is your insurance policy against “where did this spring go?” panic later.

1. Remove the top of the carb (usually 4-6 screws). This exposes the float, needle valve, and sometimes the choke mechanism.
2. Carefully remove the float and needle valve. If the float is brass and dented, replace it. If it’s plastic and cracked, same deal.
3. Pop out the float pin. A small punch or even a nail works if it’s stuck. Don’t force it—you’ll bend the float mounts.
4. Remove the main jets, pilot jets, and emulsion tubes. These are the tiny brass pieces screwed into the carb body. Use a proper jet screwdriver or you’ll strip them.
5. Take out the throttle plate and choke plate screws. These often hide behind springs or clips.
6. Separate the throttle body from the base if your carb is a two-piece design.

This is where the magic happens. You’ll need:

• A parts cleaning basket or small container.
• Enough carb cleaner to submerge the parts.
• An old toothbrush or soft-bristle brush.

1. Soak all metal parts (except rubber or plastic) in carb cleaner for 30-60 minutes. Don’t rush this—varnish needs time to dissolve.
2. After soaking, scrub every passage, jet, and crevice with a brush. Pay special attention to:
   • The tiny holes in the main jets and emulsion tubes.
   • The idle mixture screws (these get clogged 90% of the time).
   • The throttle shaft bores—carbon builds up here and causes sticking.
3. Use compressed air to blow out every passage. Hold the part up to a light—if you can’t see through it, it’s not clean.
4. For stubborn clogs, use a piece of fine wire or a drill bit smaller than the jet opening. Never ream out jets with a larger bit—you’ll ruin the calibration.

Now that everything is clean, it’s time to put it back together. This is where most DIYers mess up—rushing or forgetting a tiny part. Take your time.

1. Install new gaskets and seals from your rebuild kit. Never reuse old gaskets—they’ll leak.
2. Reinstall the jets and emulsion tubes. Finger-tighten them first, then snug with a screwdriver. Don’t overtighten—you’ll strip the soft brass.
3. Reattach the float and needle valve. Set the float height according to your service manual (usually 1/8” to 1/4” from the gasket surface).
4. Reinstall the throttle and choke plates. Make sure they open and close smoothly—no binding.
5. Reattach the top of the carburetor. Torque screws evenly to avoid warping the flange.

Now for the moment of truth. Reinstall the carburetor:

1. Remove the rag from the intake manifold and lower the carb into place. Start all bolts by hand to avoid cross-threading.
2. Tighten the bolts in a crisscross pattern to 15-20 ft-lbs (don’t overtighten—you’ll warp the flange).
3. Reconnect all hoses, linkages, and electrical connections. Double-check your labels!
4. Reinstall the air cleaner.
5. Start the engine. It may take a few cranks to prime the carb. Listen for leaks or unusual noises.

Once it’s running, you’ll need to adjust the carburetor:

• Set the idle speed (usually 600-800 RPM for cars, 1,000-1,200 RPM for motorcycles).
• Adjust the idle mixture screws for the smoothest idle (turn slowly—1/8 turn at a time).
• Check for acceleration stumble. If it bogs, the accelerator pump may need adjustment.