Craftsman 42cc Chainsaw Carburetor Replacement (5 Expert Tips)

If you have a Craftsman 42cc chainsaw, replacing the carburetor might seem daunting, but with the right approach, it’s a task you can tackle yourself. I’ve found that choosing a carburetor specifically designed as an OEM replacement for your model is almost always the best option. After years of tinkering with chainsaws, I’ve learned that generic parts can lead to more headaches than they’re worth. This guide will walk you through the process with expert tips I’ve gathered over countless carburetor swaps.

Craftsman 42cc Chainsaw Carburetor Replacement: 5 Expert Tips

1. Diagnosing the Carburetor Issue

Before diving into the replacement, let’s make sure the carburetor is truly the problem. I can’t tell you how many times I’ve seen folks replace a perfectly good carburetor, only to find the issue was something else entirely.

Symptoms of a Faulty Carburetor:
- Hard starting: The chainsaw refuses to start, or it takes excessive pulling.
- Rough idling: The engine idles erratically or stalls frequently.
- Poor performance: The chainsaw lacks power, bogs down under load, or stalls when accelerating.
- Fuel leakage: Fuel leaks from the carburetor or around the air filter.
Troubleshooting Steps:
- Check the fuel: Old or contaminated fuel is a common culprit. Drain the tank and replace it with fresh fuel mixed with the correct ratio of 2-cycle oil (typically 40:1 or 50:1, but always refer to your chainsaw’s manual). I once spent an entire afternoon troubleshooting a chainsaw that simply had bad gas.
- Inspect the fuel lines: Look for cracks, leaks, or blockages. Replace any damaged fuel lines.
- Clean the air filter: A dirty air filter restricts airflow, causing the engine to run poorly. Clean or replace the air filter.
- Check the spark plug: A fouled or damaged spark plug can cause starting and performance problems. Clean or replace the spark plug. The spark plug gap for most Craftsman 42cc chainsaws is around 0.025 inches.
- Adjust the carburetor: Sometimes, a simple carburetor adjustment can solve the problem. However, if the carburetor is severely clogged or damaged, adjustment won’t help.
When to Replace the Carburetor: If you’ve gone through these troubleshooting steps and the chainsaw still isn’t running correctly, it’s likely time for a new carburetor. Specifically, if you notice visible damage to the carburetor body, persistent fuel leaks, or if cleaning the carburetor doesn’t improve performance, replacement is the best course of action.

Takeaway: Don’t jump to carburetor replacement without thorough troubleshooting. You might save yourself time and money by addressing a simpler issue.

2. Gathering the Right Tools and Parts

Having the right tools and parts on hand will make the carburetor replacement process much smoother. Trust me, there’s nothing more frustrating than getting halfway through a project and realizing you’re missing a crucial tool.

Tools You’ll Need:
- Screwdrivers: A Phillips head and a flathead screwdriver of appropriate sizes.
- Pliers: Needle-nose pliers are particularly useful for removing fuel lines and small parts.
- Socket set or wrench set: To remove any bolts or nuts securing the carburetor.
- Carburetor cleaner: To clean any residual dirt or debris.
- Small brushes: For cleaning tight spaces.
- Shop rags: To wipe up fuel and keep your workspace clean.
- Gloves: To protect your hands from fuel and chemicals.
- Safety glasses: To protect your eyes from debris.
Parts You’ll Need:
- Replacement carburetor: Make sure it’s the correct part number for your Craftsman 42cc chainsaw. Cross-reference the model number of your chainsaw with the carburetor manufacturer’s specifications. I always recommend buying an OEM (Original Equipment Manufacturer) or a reputable aftermarket carburetor.
- New fuel lines: Fuel lines can become brittle and cracked over time, so it’s a good idea to replace them when you replace the carburetor.
- New fuel filter: The fuel filter keeps debris out of the carburetor. Replace it to ensure a clean fuel supply.
- New air filter: A clean air filter is essential for proper engine performance.
- New spark plug: Replacing the spark plug is a good practice when performing other engine maintenance.
- Gaskets: Carburetor gaskets ensure a tight seal between the carburetor and the engine. Replace them to prevent air leaks.
Where to Buy Parts:
- Local lawnmower repair shops: These shops often carry OEM and aftermarket parts for Craftsman chainsaws.
- Online retailers: Amazon, eBay, and other online retailers offer a wide selection of carburetor parts. Be sure to check the seller’s reviews and the part’s compatibility with your chainsaw model.
- Craftsman parts dealers: You can order parts directly from Craftsman or an authorized Craftsman dealer.

Takeaway: Invest in quality tools and parts. It will make the job easier and ensure the longevity of your chainsaw. Always double-check the part numbers to ensure compatibility.

3. Step-by-Step Carburetor Replacement

Now, let’s get down to the actual carburetor replacement. I’ve broken it down into manageable steps to make the process as clear as possible.

Step 1: Preparation
- Disconnect the spark plug wire: This is a crucial safety step to prevent accidental starting.
- Drain the fuel tank: Use a fuel siphon or carefully tip the chainsaw over to drain the fuel into a suitable container. Dispose of the fuel properly.
- Clean the area around the carburetor: Use a brush or compressed air to remove any dirt or debris.
Step 2: Removing the Old Carburetor
- Remove the air filter cover and air filter: Set them aside.
- Disconnect the fuel lines: Use needle-nose pliers to carefully disconnect the fuel lines from the carburetor. Note their positions for reinstallation. Fuel lines are often marked with arrows indicating the direction of fuel flow.
- Disconnect the throttle linkage and choke linkage: These linkages connect the carburetor to the throttle and choke controls. Note how they are connected before disconnecting them. Take a picture with your phone if necessary.
- Remove the carburetor mounting bolts or screws: These bolts or screws secure the carburetor to the engine. Loosen and remove them.
- Carefully remove the old carburetor: Gently pull the carburetor away from the engine. Be careful not to damage any surrounding parts.
Step 3: Installing the New Carburetor
- Install new gaskets: Place new gaskets on the engine and carburetor mounting surfaces.
- Attach the new carburetor: Align the carburetor with the mounting holes and secure it with the mounting bolts or screws. Tighten the bolts or screws to the manufacturer’s specified torque.
- Connect the throttle linkage and choke linkage: Reconnect the throttle linkage and choke linkage to the carburetor. Make sure they are properly adjusted.
- Connect the fuel lines: Reconnect the fuel lines to the carburetor, making sure to connect them to the correct ports.
- Install the air filter and air filter cover: Replace the air filter and air filter cover.
Step 4: Final Checks and Adjustments
- Check for fuel leaks: Add a small amount of fuel to the tank and check for any leaks around the carburetor and fuel lines.
- Connect the spark plug wire: Reconnect the spark plug wire.
- Start the chainsaw: Follow the manufacturer’s instructions for starting the chainsaw.
- Adjust the carburetor: Adjust the carburetor according to the manufacturer’s instructions. Most carburetors have two or three adjustment screws:
  - “L” screw: Adjusts the low-speed fuel mixture.
  - “H” screw: Adjusts the high-speed fuel mixture.
  - “LA” screw: Adjusts the idle speed.
  - Start by turning both the “L” and “H” screws clockwise until they are lightly seated. Then, back them out 1 to 1.5 turns. Start the chainsaw and adjust the “LA” screw until the engine idles smoothly without stalling. Fine-tune the “L” and “H” screws for optimal performance.

Takeaway: Take your time and pay attention to detail. Proper installation and adjustment are crucial for optimal chainsaw performance. Consider recording a video as you disassemble the old carburetor, which can be invaluable during reassembly.

4. Carburetor Adjustment and Tuning

Even a brand-new carburetor might need some fine-tuning to get your chainsaw running its best. This is where my experience really comes in handy.

Understanding Carburetor Adjustment Screws:
- Low-Speed (L) Screw: Controls the fuel mixture at idle and low speeds. Adjusting this screw affects the chainsaw’s ability to start easily and idle smoothly.
- High-Speed (H) Screw: Controls the fuel mixture at high speeds and under load. Adjusting this screw affects the chainsaw’s power output and prevents engine damage from running too lean.
- Idle Speed (LA) Screw: Controls the engine’s idle speed. Adjusting this screw prevents the chainsaw from stalling at idle.
Carburetor Adjustment Procedure:
- Warm up the engine: Let the chainsaw run for a few minutes to warm up the engine.
- Adjust the idle speed: Turn the idle speed (LA) screw clockwise to increase the idle speed or counterclockwise to decrease the idle speed. Adjust the idle speed until the engine idles smoothly without stalling. The ideal idle speed for most Craftsman 42cc chainsaws is around 2,700-3,200 RPM.
- Adjust the low-speed mixture: Turn the low-speed (L) screw clockwise to lean the mixture or counterclockwise to richen the mixture. Adjust the low-speed mixture until the engine accelerates smoothly from idle to full throttle.
- Adjust the high-speed mixture: Turn the high-speed (H) screw clockwise to lean the mixture or counterclockwise to richen the mixture. Adjust the high-speed mixture until the engine runs smoothly at full throttle without bogging down or stalling. A slightly rich mixture is generally safer than a lean mixture, as it helps to prevent engine damage from overheating.
Signs of a Lean or Rich Mixture:
- Lean Mixture (Too Much Air):
  - Engine runs hot.
  - Engine hesitates or bogs down under load.
  - Spark plug is white or light gray.
- Rich Mixture (Too Much Fuel):
  - Engine runs sluggishly.
  - Engine smokes excessively.
  - Spark plug is black and sooty.
Tools for Carburetor Adjustment:
- Tachometer: A tachometer is a useful tool for measuring engine speed and ensuring that the idle speed is properly set.
- Screwdriver with a small head: A small screwdriver is needed to adjust the carburetor screws.
Safety Precautions:
- Wear safety glasses to protect your eyes from debris.
- Wear gloves to protect your hands from fuel and chemicals.
- Work in a well-ventilated area.
- Keep the chainsaw away from flammable materials.

Takeaway: Carburetor adjustment is a delicate process. Make small adjustments and listen to the engine. If you’re unsure, consult a qualified technician. Always err on the side of a slightly rich mixture to protect your engine.

5. Maintenance and Prevention

Once you’ve replaced and adjusted your carburetor, proper maintenance is key to keeping your chainsaw running smoothly for years to come. I’ve seen firsthand how consistent maintenance can extend the life of a chainsaw significantly.

Fuel System Maintenance:
- Use fresh fuel: Always use fresh fuel mixed with the correct ratio of 2-cycle oil. Old fuel can gum up the carburetor and cause starting and performance problems. I recommend using fuel stabilizer, especially if you’re not going to use the chainsaw for an extended period.
- Drain the fuel tank: If you’re not going to use the chainsaw for more than a month, drain the fuel tank and run the engine until it stalls to remove any fuel from the carburetor.
- Clean the fuel filter: Clean the fuel filter regularly to prevent debris from clogging the carburetor.
- Inspect the fuel lines: Inspect the fuel lines regularly for cracks, leaks, or blockages. Replace any damaged fuel lines.
Air Filter Maintenance:
- Clean the air filter regularly: Clean the air filter after each use or more frequently if you’re working in dusty conditions. A dirty air filter restricts airflow and causes the engine to run poorly.
- Replace the air filter: Replace the air filter when it becomes excessively dirty or damaged.
Spark Plug Maintenance:
- Clean the spark plug: Clean the spark plug regularly to remove carbon deposits.
- Check the spark plug gap: Check the spark plug gap and adjust it to the manufacturer’s specifications. The spark plug gap for most Craftsman 42cc chainsaws is around 0.025 inches.
- Replace the spark plug: Replace the spark plug when it becomes fouled or damaged.
Carburetor Cleaning:
- Use carburetor cleaner: Use carburetor cleaner to clean the carburetor regularly. This will help to remove any gum or varnish deposits that can clog the carburetor.
- Disassemble and clean the carburetor: If the carburetor is severely clogged, you may need to disassemble it and clean each part individually.
Storage:
- Store the chainsaw properly: When storing the chainsaw, drain the fuel tank, clean the air filter, and remove the spark plug. Store the chainsaw in a dry, well-ventilated area.
Regular Inspections:
- Inspect the chainsaw regularly: Inspect the chainsaw regularly for any signs of damage or wear. Pay particular attention to the fuel lines, air filter, spark plug, and carburetor.
Sharpening the Chain:
- Keep the chain sharp: A sharp chain is essential for safe and efficient cutting. Sharpen the chain regularly using a chainsaw file or a chain grinder.
Chain Lubrication:
- Use chain oil: Always use chain oil to lubricate the chain. Chain oil helps to reduce friction and wear and tear on the chain and bar.
Professional Servicing:
- Seek professional help: If you’re not comfortable performing chainsaw maintenance yourself, take the chainsaw to a qualified technician for servicing.

Takeaway: Regular maintenance is the key to keeping your Craftsman 42cc chainsaw running smoothly and efficiently. A little preventative care can save you a lot of headaches (and money) in the long run.

Additional Tips and Tricks

Over the years, I’ve picked up a few extra tips and tricks that can make carburetor replacement and chainsaw maintenance even easier.

Use a Parts Diagram: A parts diagram can be invaluable when disassembling and reassembling the carburetor. It shows the location of each part and how they fit together. You can usually find a parts diagram online or in the chainsaw’s owner’s manual.
Take Pictures: Before disassembling the carburetor, take pictures of each step. This will help you remember how everything goes back together.
Label Parts: As you disassemble the carburetor, label each part with a piece of tape. This will help you avoid confusion when reassembling the carburetor.
Use a Carburetor Cleaning Kit: A carburetor cleaning kit contains all the tools and chemicals you need to clean the carburetor thoroughly.
Ultrasonic Cleaner: For heavily clogged carburetors, an ultrasonic cleaner can be very effective. The ultrasonic waves create tiny bubbles that dislodge dirt and debris from hard-to-reach areas.
Compressed Air: Use compressed air to blow out any remaining dirt or debris from the carburetor after cleaning.
Check for Air Leaks: After replacing the carburetor, check for air leaks around the carburetor and intake manifold. Air leaks can cause the engine to run poorly. You can use a carburetor cleaner or starting fluid to check for air leaks. Spray the carburetor cleaner or starting fluid around the carburetor and intake manifold while the engine is running. If the engine speed changes, there is an air leak.
Use a Vacuum Tester: A vacuum tester can be used to check the engine’s vacuum. Low vacuum can indicate a problem with the engine, such as a worn piston or cylinder.
Use a Compression Tester: A compression tester can be used to check the engine’s compression. Low compression can indicate a problem with the engine, such as worn piston rings or valves.
Check the Ignition System: If the chainsaw is still not running correctly after replacing the carburetor, check the ignition system. The ignition system is responsible for providing the spark that ignites the fuel mixture.
Check the Exhaust System: A clogged exhaust system can also cause the engine to run poorly. Check the exhaust system for any blockages.
Consult a Professional: If you’re not comfortable performing any of these tasks yourself, consult a qualified technician.

Takeaway: These additional tips and tricks can help you troubleshoot and maintain your Craftsman 42cc chainsaw more effectively. Don’t be afraid to experiment and learn from your experiences.

Common Mistakes to Avoid

Even experienced chainsaw users can make mistakes when replacing a carburetor. Here are some common pitfalls to watch out for:

Using the Wrong Carburetor: Make sure you are using the correct carburetor for your Craftsman 42cc chainsaw. Using the wrong carburetor can cause the engine to run poorly or not at all.
Forgetting to Disconnect the Spark Plug Wire: This is a crucial safety step. Forgetting to disconnect the spark plug wire can result in accidental starting and injury.
Damaging Fuel Lines: Fuel lines can be brittle and easily damaged. Use caution when disconnecting and reconnecting fuel lines.
Over-Tightening Bolts: Over-tightening bolts can strip the threads or damage the carburetor. Tighten bolts to the manufacturer’s specified torque.
Losing Small Parts: Carburetors contain many small parts that can be easily lost. Work in a clean, well-lit area and keep track of all the parts.
Ignoring Gaskets: Gaskets are essential for ensuring a tight seal between the carburetor and the engine. Always replace gaskets when replacing the carburetor.
Improper Carburetor Adjustment: Improper carburetor adjustment can cause the engine to run poorly or not at all. Follow the manufacturer’s instructions for carburetor adjustment.
Using Old Fuel: Old fuel can gum up the carburetor and cause starting and performance problems. Always use fresh fuel.
Neglecting Maintenance: Neglecting maintenance can lead to a variety of problems, including carburetor failure. Perform regular maintenance to keep your chainsaw running smoothly.
Ignoring Safety Precautions: Always follow safety precautions when working on a chainsaw. Wear safety glasses, gloves, and work in a well-ventilated area.

Takeaway: Avoiding these common mistakes can save you time, money, and frustration. Pay attention to detail and follow the instructions carefully.

Replacing the carburetor on your Craftsman 42cc chainsaw doesn’t have to be a daunting task. By following these expert tips, you can confidently tackle the job and get your chainsaw running like new again. Remember to prioritize safety, take your time, and pay attention to detail. With a little patience and the right tools, you can keep your chainsaw in top condition for years to come.

Craftsman 42cc Chainsaw Carburetor Replacement (5 Expert Tips)