I'm at my wit's end with my 2013 Thor Class C's Onan 4000 generator! It's been sitting since March (I know, I know...) and now I'm dealing with a nightmare. Been getting Code 14 errors and spent half the morning just trying to get it fired up.
The only way I can get it started is by manually messing with what I think is the choke linkage - otherwise it just won't go. Once I shut it off, same story - won't restart unless I physically manipulate that linkage again. Only has 240 hours on it and was serviced about 2 years ago.
I'm pretty sure the carburetor is gummed up from sitting, but what exactly does Code 14 mean? And more importantly, what do I need to clean to get that choke working automatically again? I really need to get this thing running properly before our next trip!
Code 14 is overspeed but your real issue is carburetor gummed from sitting. Choke mechanism needs cleaning to operate automatically. Clean carburetor thoroughly - jets and choke linkage. Use fresh fuel and add stabilizer to prevent future issues.
Your 2013 Thor Class C with the Onan 4000 generator is experiencing classic carburetor gumming issues from sitting idle since March. The Code 14 error and need to manually manipulate the choke linkage to start indicates the carburetor's fuel passages are partially blocked with varnish and deposits. Even with only 240 hours and service 2 years ago, ethanol fuel degrades quickly and creates sticky residues that prevent proper fuel flow and choke operation. This is a very common issue with Onan generators that sit unused for extended periods, and you're right on track thinking it's carburetor-related.
The primary culprit is fuel degradation from your 8-month storage period. Ethanol-blended gasoline can start breaking down and form gum and varnish that clogs the carburetor's small passages, particularly the pilot jet and choke circuits. Your Onan 4000 uses a Nikki carburetor with very precise fuel metering, making it sensitive to even small blockages.
Code 14 typically indicates an underspeed/no oil pressure shutdown condition, though the symptoms described suggest carburetor issues affecting startup. This happens when the carburetor can't deliver the right fuel mixture during startup. The choke linkage you're manipulating controls the butterfly valve that enriches the fuel mixture for cold starts - when you manually adjust it, you're compensating for the carburetor's inability to function properly.
Additional factors include water contamination in the fuel system, a stuck float in the carburetor bowl, and potential issues with the fuel pump diaphragm. However, given your specific symptoms and the extended sitting period, carburetor cleaning is your most likely solution.
SAFETY WARNING: Before beginning any fuel system work, disconnect the battery and shut off the fuel supply valve. Ensure the generator is completely cool and has not been running for at least one hour. Work in a well-ventilated area away from ignition sources. Have a fire extinguisher nearby when working with fuel components.
Start by gathering the necessary supplies: carburetor cleaner spray (Berryman B-12 Chemtool works well), a carburetor rebuild kit for the correct part for your model (verify with dealer), basic hand tools including screwdrivers and wrenches, and safety equipment including gloves and eye protection. You'll also need fresh gasoline and potentially a fuel stabilizer for future storage.
Locate your generator's service manual or download it from Cummins Onan's website using your model and serial numbers. Take photos of the carburetor linkages and connections before disassembly - this will be invaluable during reassembly. Ensure you have adequate workspace and lighting, as carburetor work requires attention to small parts and precise adjustments.
Check your fuel supply first by draining the carburetor bowl using the drain screw on the bottom. If the fuel smells varnish-like or appears cloudy, you'll definitely need to address fuel system contamination in addition to carburetor cleaning. Consider having compressed air available for blowing out passages, though avoid using excessive pressure that could damage delicate components.
SAFETY WARNING: Allow generator to cool completely before servicing. Hot exhaust components can cause severe burns. Be aware that fuel system components may retain pressure.
Begin by removing the air cleaner assembly and disconnecting the fuel line at the carburetor. Disconnect the fuel shutoff solenoid and any other electrical connections. Take detailed photos of all linkage positions, then disconnect the choke and throttle linkages. Remove the two nuts securing the carburetor to the intake manifold - check manufacturer specifications for proper socket size. Lift the carburetor straight up to avoid damaging the gasket surfaces.
Remove the float bowl by unscrewing the four screws on the bottom. Inspect the float and needle valve assembly - the needle should move freely and seal completely against its seat. Remove the main jet (check manufacturer specifications for correct size) and pilot jet (smaller, often requires a flat-blade screwdriver). Clean all jets thoroughly with carburetor cleaner and compressed air, ensuring all passages are completely clear.
Pay special attention to the choke mechanism. The choke butterfly should move freely without binding, and the thermostatic spring should provide proper tension. Clean the choke housing thoroughly and check that the heat tube from the exhaust manifold isn't blocked, as this affects automatic choke operation. If the choke isn't operating smoothly, this explains why manual manipulation was necessary to start your generator.
Reassemble using new gaskets from your rebuild kit, ensuring proper torque to manufacturer specifications on all fasteners. Reinstall the carburetor with a new intake manifold gasket, reconnect all linkages according to your photos, and refill with fresh gasoline. Before starting, prime the fuel system according to your generator's procedure (method varies by fuel pump type - mechanical or electric).
Consider professional service if you discover significant internal carburetor damage such as a stuck float, damaged needle valve seat, or stripped threads in the carburetor body. These issues often require specialized tools or replacement parts that may exceed the cost-effectiveness of DIY repair on a generator with low hours like yours.
If cleaning the carburetor doesn't resolve the starting issues and Code 14 persists, the problem may lie in other systems such as the ignition module, stator assembly, or internal engine timing. These require diagnostic equipment and expertise beyond typical DIY capabilities. Additionally, if you're uncomfortable working with fuel systems or lack mechanical experience, professional service ensures safety and proper repair.
Call a certifiedied Onan dealer if your generator is still under extended warranty coverage, as DIY carburetor work might affect warranty claims. However, with a 2013 model, you're likely past standard warranty periods. Professional carburetor service typically runs $300-500, while a complete cleaning kit costs around $30-50 for DIY repair, making this an excellent candidate for owner maintenance given your mechanical inclination evidenced by successfully diagnosing the choke linkage issue.
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