Introduction
Onan generators are a popular power solution for RVs, food trucks, and mobile businesses. They’re known for their reliability, but like any engine, they require periodic maintenance. One of the most common issues with aging Onan generators is a clogged or faulty carburetor. When cleaning no longer helps, carburetor replacement becomes necessary.
In this guide, you’ll learn everything about Onan carburetor replacement including signs of failure, tools needed, step-by-step instructions, and post-installation tips. Whether you're a DIY enthusiast or considering professional help, this article gives you a clear roadmap to restore your generator’s performance.
Why Carburetor Replacement Matters
The carburetor mixes air and fuel for combustion. Over time, varnish from old fuel, dust, or corrosion can block jets or passages inside the unit. A malfunctioning carburetor can lead to:
Hard starting or failure to start
Rough idle or stalling
Black smoke from the exhaust
Excessive fuel consumption
Unreliable generator performance
Replacing the carburetor restores engine efficiency and ensures smooth generator operation—especially important when you're relying on power off-grid.
Signs You Need to Replace Your Onan Carburetor
Before you replace the carburetor, confirm that it's the root cause of the issue. Here are some warning signs:
1. Generator Runs Rough or Stalls
A clogged or damaged carburetor can disrupt the air-fuel mixture, causing the engine to stall or surge.
2. Hard Starts After Sitting
If your generator hasn’t been run in a while and now won’t start—even with fresh fuel—the carburetor may be gummed up.
3. Poor Fuel Efficiency
A rich fuel mixture can burn more fuel than necessary, indicating that the carburetor needs attention.
4. Excessive Smoke or Fuel Smell
Leaking or flooding carburetors can produce smoke and strong fuel odors—signs of internal failure.
Tools and Materials You’ll Need
Before replacing your Onan carburetor, gather the following:
Replacement carburetor (model-specific)
Screwdrivers (Phillips and flathead)
Socket set and ratchet
Fuel line clamps or pinch-off pliers
New gaskets or O-rings (usually come with carburetor)
Safety gloves and eye protection
Carburetor cleaner (for surrounding area)
Container to catch fuel
Pro Tip: Always use OEM or high-quality aftermarket parts specific to your generator model.
Step-by-Step Onan Carburetor Replacement
Note: These steps apply to most Onan RV generators such as the Onan 4000 (Microquiet), Onan 5500, and Onan 6500 series.
Step 1: Turn Off Power and Fuel Supply
Shut down the generator.
Disconnect the negative battery terminal to prevent accidental starts.
Turn off the fuel valve or pinch the fuel line to prevent spills.
Step 2: Access the Generator Compartment
Remove the service panel or access cover on the generator.
Identify the carburetor—it’s usually attached to the side of the engine block and connected to the air intake and fuel line.
Step 3: Disconnect Fuel Line and Linkages
Use pliers to loosen the fuel clamp and carefully disconnect the line.
Remove throttle and choke linkages. Take a photo first so you remember the correct positions.
Step 4: Remove Mounting Bolts
Use a socket wrench to unbolt the carburetor from the intake manifold.
Carefully pull the carburetor away. Be sure to remove the old gasket.
Step 5: Install the New Carburetor
Attach a new gasket or O-ring.
Position the new carburetor and secure it with the mounting bolts.
Reconnect throttle and choke linkages.
Reattach the fuel line and clamp it securely.
Step 6: Double Check Connections
Ensure all bolts are tight and linkages move freely.
Look for potential leaks or misalignments.
Step 7: Reconnect Battery and Test
Reconnect the negative battery terminal.
Start the generator and let it run for several minutes.
Listen for smooth operation and check for fuel leaks.
Post-Installation Tips
After a successful replacement, follow these tips for long-term performance:
Use fresh, stabilized fuel to prevent clogging.
Run the generator monthly for 30 minutes to circulate fuel.
Clean the air filter regularly for proper airflow.
Keep spare gaskets and fuel line clamps on hand in case of future maintenance.
When to Call a Professional
If you're uncomfortable handling fuel systems or dealing with tight generator compartments, it’s best to call an RV technician. Also, consider professional help if:
The generator is under warranty
You’re unable to remove the old carburetor
The new carburetor doesn’t fix the issue
Recommended Onan Replacement Carburetors
Make sure you buy a replacement that matches your Onan model. Here are some popular choices:
Onan 146-0703 Carburetor – Fits many Onan 4000 Microquiet models
Onan 146-0774 – For Onan 5500 Marquis Gold series
Onan 146-0656 – Works with older Emerald Plus units
Always cross-reference the part number with your generator’s model before purchasing.
Conclusion
Replacing your Onan generator's carburetor can breathe new life into your power system. With the right tools, a little patience, and the proper replacement part, many RV owners can perform this repair on their own. Keeping your generator in top condition ensures a reliable power source during every adventure, whether you’re boondocking or road tripping across the country.
