Carburetor For Stihl Blower: Replace & Tune Your SH 85C (Pro Tips)

Alright, folks, gather ’round! Ever feel like your Stihl SH 85C blower is wheezing more than it’s blowing? Like it’s trying to whisper sweet nothings to the leaves instead of blasting them into next week? Chances are, you’re looking at a carburetor issue. And don’t worry, I’m not going to sugarcoat it – carbs can be finicky little devils. But with a little know-how and a dash of patience, you can tackle this job yourself. I’m going to walk you through the process of replacing and tuning the carburetor on your Stihl SH 85C blower, giving you the “pro tips” you need to get the job done right.

Why is Carburetor Maintenance Important for Wood Processing & Firewood Prep?

Now, you might be thinking, “What does a blower have to do with wood processing and firewood?” Well, a clean worksite is a safe worksite. A blower is essential for clearing sawdust, wood chips, and debris from your workspace, ensuring you don’t slip, trip, or set off a rogue spark with a hidden pile of tinder-dry shavings. Plus, a well-maintained blower means a more efficient you, which translates to more firewood stacked and less time spent cleaning.

Key Terms & Concepts

Before we dive into the nitty-gritty, let’s establish some common ground:

Carburetor: The heart of your blower’s engine, responsible for mixing air and fuel in the correct ratio for combustion. A faulty carb leads to poor performance, hard starting, or even a complete failure to run.
Fuel-Air Ratio: The ideal balance of air and fuel needed for efficient combustion. Too much fuel (rich) or too little fuel (lean) can cause problems.
Idle Speed: The engine’s RPM when the throttle is released.
High-Speed Needle: A carburetor adjustment screw that controls the fuel flow at high engine speeds.
Low-Speed Needle: A carburetor adjustment screw that controls the fuel flow at idle and low engine speeds.
Choke: A device that restricts airflow to enrich the fuel mixture, used primarily for starting a cold engine.
Primer Bulb: A small rubber bulb that pumps fuel into the carburetor to aid in starting.
Green Wood vs. Seasoned Wood: Green wood is freshly cut and has a high moisture content. Seasoned wood has been dried, making it ideal for burning. Moisture content targets for firewood generally range from 15-20%.

Step-by-Step Guide: Replacing Your Stihl SH 85C Carburetor

Alright, let’s get our hands dirty. I’ve replaced countless carbs on various small engines, and the Stihl SH 85C is a pretty straightforward one. Follow these steps carefully:

1. Gathering Your Tools & Materials

Before you even think about touching your blower, make sure you have everything you need. This prevents frustrating interruptions and ensures a smooth process.

New Carburetor: Make sure it’s the correct one for your Stihl SH 85C. Double-check the part number. I once ordered the wrong carb for a chainsaw and wasted an entire afternoon trying to make it fit – don’t be like me!
Screwdriver Set: You’ll need both flathead and Phillips head screwdrivers.
Pliers: For removing fuel lines and other small components.
Socket Set: A small socket set can be helpful for removing the air filter cover.
Carburetor Adjustment Tool (Screwdriver): Many Stihl carburetors use a special “D” shaped adjustment tool. You can find these online or at your local small engine repair shop.
Clean Rags: For wiping up fuel spills.
Fuel Line Clamp (Optional): These prevent fuel from leaking when you disconnect the fuel lines.
Work Gloves: Protect your hands.
Safety Glasses: Safety first!
Carburetor Cleaner: For cleaning the surrounding area.
Small Brush: For removing debris.
Camera or Phone: Take pictures as you disassemble the blower. This is invaluable for reassembly, especially if you’re a beginner.

2. Preparing Your Work Area

Find a well-ventilated area to work on your blower. Gasoline fumes can be dangerous, so good ventilation is crucial. Lay down some newspaper or a drop cloth to protect your work surface from fuel spills.

3. Disconnecting the Spark Plug

This is a critical safety step. Disconnecting the spark plug prevents the engine from accidentally starting while you’re working on it. Locate the spark plug wire and pull it off the spark plug.

4. Removing the Air Filter Cover & Air Filter

Use a screwdriver or socket to remove the air filter cover. Once the cover is off, remove the air filter. Inspect the air filter – if it’s dirty, replace it. A clean air filter is essential for proper engine performance.

5. Removing the Carburetor Cover

You’ll likely need to remove a plastic cover to access the carburetor. This cover is usually held in place by screws. Remove the screws and carefully remove the cover.

6. Disconnecting the Fuel Lines

This is where things can get a little messy. Before disconnecting the fuel lines, take a picture of how they’re connected. This will save you a lot of headache during reassembly. Use pliers to gently remove the fuel lines from the carburetor. If you have fuel line clamps, use them to pinch off the fuel lines to prevent fuel from leaking.

7. Disconnecting the Throttle Linkage & Choke Linkage

The throttle linkage and choke linkage connect the carburetor to the throttle and choke controls. Carefully disconnect these linkages from the carburetor. Again, take a picture before disconnecting them! These small linkages can be tricky to reattach if you don’t know how they go.

8. Removing the Old Carburetor

With the fuel lines and linkages disconnected, you can now remove the old carburetor. It’s usually held in place by screws. Remove the screws and carefully pull the carburetor away from the engine.

9. Inspecting the Intake Manifold & Mounting Surface

Before installing the new carburetor, inspect the intake manifold and mounting surface for any dirt, debris, or damage. Clean the area with carburetor cleaner and a small brush. Make sure the mounting surface is smooth and free of any obstructions.

10. Installing the New Carburetor

Now, the moment we’ve been waiting for! Install the new carburetor in the reverse order of removal.

Attach the Carburetor: Align the carburetor with the intake manifold and secure it with the screws.
Reconnect the Throttle Linkage & Choke Linkage: Carefully reconnect the throttle linkage and choke linkage to the carburetor. Refer to the pictures you took earlier to ensure they’re connected correctly.
Reconnect the Fuel Lines: Reconnect the fuel lines to the carburetor. Make sure they’re securely attached and that they’re connected to the correct ports.
Reinstall the Carburetor Cover: Reinstall the plastic cover that protects the carburetor.
Reinstall the Air Filter & Air Filter Cover: Reinstall the air filter and air filter cover.
Reconnect the Spark Plug: Reconnect the spark plug wire to the spark plug.

Tuning Your Stihl SH 85C Carburetor: The Art of the Perfect Mix

Replacing the carburetor is only half the battle. You also need to tune it to ensure it’s running optimally. Tuning involves adjusting the high-speed and low-speed needles to achieve the correct fuel-air ratio.

1. Understanding Carburetor Adjustment Screws

Most Stihl carburetors have two adjustment screws:

High-Speed Needle (H): Controls the fuel flow at high engine speeds.
Low-Speed Needle (L): Controls the fuel flow at idle and low engine speeds.

Some carburetors may also have an idle speed adjustment screw (T). This screw adjusts the engine’s RPM when the throttle is released.

2. The Importance of a Tachometer (Optional but Recommended)

While you can tune a carburetor by ear, using a tachometer provides a more accurate and reliable result. A tachometer measures the engine’s RPM, allowing you to fine-tune the carburetor to the manufacturer’s specifications.

3. Initial Carburetor Settings

Before starting the engine, set the high-speed and low-speed needles to their initial settings. These settings are usually listed in the owner’s manual. If you don’t have the owner’s manual, a good starting point is to turn both needles all the way in (clockwise) until they’re lightly seated, and then back them out 1 to 1.5 turns.

4. Starting the Engine

Start the engine and let it warm up for a few minutes. This allows the engine to reach operating temperature and ensures a more accurate tuning.

5. Adjusting the Low-Speed Needle (L)

The low-speed needle affects the engine’s idle and low-speed performance. To adjust the low-speed needle, turn it slowly in either direction until the engine idles smoothly. If the engine stalls or runs rough at idle, try adjusting the low-speed needle slightly in either direction until it smooths out.

Lean Condition (Too Little Fuel): If the engine idles high, hesitates when you give it throttle, or stalls easily, it’s likely running lean. Turn the low-speed needle counterclockwise (out) to richen the mixture.

Rich Condition (Too Much Fuel): If the engine idles rough, smokes excessively, or is difficult to start, it’s likely running rich. Turn the low-speed needle clockwise (in) to lean out the mixture.

6. Adjusting the High-Speed Needle (H)

The high-speed needle affects the engine’s performance at full throttle. To adjust the high-speed needle, run the engine at full throttle and listen to the engine’s sound.

Lean Condition: If the engine screams or sounds like it’s straining at full throttle, it’s likely running lean. Turn the high-speed needle counterclockwise (out) to richen the mixture.

Rich Condition: If the engine bogs down or smokes excessively at full throttle, it’s likely running rich. Turn the high-speed needle clockwise (in) to lean out the mixture.

Using a Tachometer: If you’re using a tachometer, adjust the high-speed needle until the engine reaches the manufacturer’s recommended RPM at full throttle. This information is typically found in the owner’s manual.

7. Adjusting the Idle Speed (T)

If your carburetor has an idle speed adjustment screw (T), you can use it to fine-tune the engine’s idle speed. Turn the screw clockwise to increase the idle speed and counterclockwise to decrease the idle speed. Adjust the idle speed until the engine idles smoothly without stalling.

8. Fine-Tuning & Testing

After making adjustments to the high-speed and low-speed needles, fine-tune the carburetor by making small adjustments and testing the engine’s performance. Start by making small adjustments (1/8 turn or less) and then test the engine’s performance at various throttle positions. Pay attention to the engine’s sound, responsiveness, and smoothness.

9. The “Paper Bag” Test

Here’s a little trick I learned from an old-timer: the “paper bag” test. While the engine is running at full throttle, quickly cover the air intake with a paper bag. This will momentarily richen the fuel mixture. If the engine runs smoother or gains RPMs when you cover the air intake, it’s likely running lean and needs to be richened up. If the engine bogs down or stalls when you cover the air intake, it’s likely running rich and needs to be leaned out.

10. Safety First: Don’t Over-Lean!

It’s crucial to avoid running the engine too lean. A lean condition can cause the engine to overheat and damage internal components. Always err on the side of slightly rich rather than lean.

Common Problems & Solutions

Even with careful tuning, you might encounter some problems. Here are a few common issues and their solutions:

Engine Won’t Start:
- Problem: No fuel reaching the carburetor.
- Solution: Check the fuel lines for clogs or kinks. Clean or replace the fuel filter. Check the primer bulb for cracks or leaks.
Engine Starts But Stalls Immediately:
- Problem: Incorrect carburetor settings.
- Solution: Readjust the low-speed needle. Make sure the choke is fully open.
Engine Runs Rough or Smokes Excessively:
- Problem: Carburetor is running too rich.
- Solution: Adjust the low-speed and high-speed needles to lean out the mixture.
Engine Lacks Power:
- Problem: Carburetor is running too lean.
- Solution: Adjust the low-speed and high-speed needles to richen the mixture.
Engine Surges or Hunts at Idle:
- Problem: Air leak in the intake system.
- Solution: Inspect the intake manifold and carburetor mounting surface for leaks. Replace any damaged gaskets or seals.
Carburetor Flooding:
- Problem: Float needle is stuck open.
- Solution: Remove the carburetor and clean the float needle and seat.

Case Study: Reviving a Neglected Stihl SH 85C

I once had a friend who inherited a Stihl SH 85C that had been sitting in his garage for years. It wouldn’t start, and he was ready to throw it away. I convinced him to let me take a look at it.

After inspecting the blower, I found that the carburetor was completely gummed up with old fuel. The fuel lines were cracked, and the air filter was clogged.

I replaced the carburetor, fuel lines, and air filter. I also cleaned the spark plug and checked the compression. After a few pulls, the engine sputtered to life.

However, it ran very rough and smoked excessively. I spent some time tuning the carburetor, adjusting the high-speed and low-speed needles until the engine ran smoothly and had good power.

In the end, I was able to revive the neglected Stihl SH 85C and save it from the landfill. My friend was thrilled, and he now uses it regularly to clean up his yard.

Strategic Advantages of DIY Carburetor Maintenance

While you could take your Stihl SH 85C to a repair shop, there are several strategic advantages to doing the carburetor replacement and tuning yourself:

Cost Savings: Repair shops can charge a significant amount for labor. Doing the job yourself saves you money.
Convenience: You can work on your blower on your own schedule, without having to wait for a repair shop to have time for you.
Knowledge & Skills: You’ll gain valuable knowledge and skills that will allow you to maintain and repair your small engines in the future.
Satisfaction: There’s a certain satisfaction that comes from fixing something yourself.

Tools, Materials, and Costs

Here’s a breakdown of the tools, materials, and costs associated with replacing and tuning your Stihl SH 85C carburetor:

New Carburetor: $20 – $50
Carburetor Adjustment Tool: $10 – $20
Screwdriver Set: $10 – $30
Pliers: $10 – $20
Socket Set: $20 – $50
Carburetor Cleaner: $5 – $10
Fuel Line Clamp (Optional): $5 – $10
Tachometer (Optional): $20 – $100

Total Cost: $90 – $290 (depending on the tools you already have and whether you choose to use a tachometer)

Drying Methods & Moisture Content Targets for Firewood

Since we’re talking about wood processing and firewood preparation, let’s touch on the importance of proper drying. Burning green wood is inefficient and produces a lot of smoke. Seasoned wood, on the other hand, burns hotter and cleaner.

Air Drying: The most common method for drying firewood. Stack the wood in a sunny, well-ventilated area. Allow the wood to dry for at least six months, or preferably a year.
Kiln Drying: A faster method for drying firewood. The wood is placed in a kiln and heated to remove moisture. Kiln-dried firewood typically has a moisture content of 15-20%.

Moisture Content Targets:

Green Wood: 30-60% moisture content
Seasoned Wood: 15-20% moisture content

Felling Techniques & Safety Considerations

If you’re felling trees for firewood, it’s essential to use proper felling techniques and prioritize safety.

Assess the Tree: Before felling a tree, assess its size, lean, and any potential hazards.
Plan Your Escape Route: Plan a clear escape route away from the falling tree.
Use Proper Safety Gear: Wear a hard hat, safety glasses, hearing protection, and chainsaw chaps.
Use Proper Felling Techniques: Use the appropriate felling techniques for the size and lean of the tree. This may involve using wedges or a felling lever.

Next Steps & Implementation Guidance

Now that you’ve learned how to replace and tune your Stihl SH 85C carburetor, it’s time to put your knowledge into practice.

Gather Your Tools & Materials: Make sure you have everything you need before you start.
Follow the Step-by-Step Guide: Carefully follow the steps outlined in this guide.
Take Your Time: Don’t rush the process. Take your time and pay attention to detail.
Ask for Help: If you’re unsure about anything, don’t hesitate to ask for help from a friend or a professional.
Practice Makes Perfect: The more you work on small engines, the better you’ll become.

With a little practice, you’ll be able to keep your Stihl SH 85C running smoothly for years to come. And who knows, maybe you’ll even become the neighborhood small engine guru! Good luck, and happy blowing!