Question : I have an Onan 4 KW gen on my motor home. It starts and sund for about 1.5 sec, then stops. The first level fault code is a 3. the second level fauld code is 36. The generator starts and runs the 1.5 seconds, then just dies as if the fuel stopped. While running, it is running fine. The engine runs up to speed with no hesitation or fuel starvation, then dies like it had been turned off. What’s going on? Can you help? The model number is XXXXXXXXXXX, and it haas less than 100 hrs on it, but it has been sitting a lot. Thanks. Randy Hackett

Answer :

The pump is producing plenty of fuel, so the fuel filter will not be suspect, as it screws into the inlet of the fuel pump.

Our prime suspect here is the carburetor.

As gas gets old, it turns to varnish and clogs up the passageways inside the carburetor, not allowing enough gas to get to the engine.

When this happens, either the engine simply will not start, or it will not run without the choke on (this reduces the amount of air getting pulled into the engine, changing the fuel/air mixture), or it will run but surges.

Another issue that varnish in the carb can cause is that the varnish may not allow the float needle to seal properly against the seat, causing the flow of gas to not shut off when the bowl is full. The result will be gas overflowing the carb and running into the cylinder, and possibly out the air intake. If the gas gets into the cylinder, it will seep past the rings and down into the crankcase. This will be evidenced by your oil level being over-full and/or the oil smelling like gas.

The only 2 solutions are to either replace the carburetor or give it a good, thorough cleaning.

To clean the carb, you must remove it, disassemble it (making sure to remove all non-metal parts), and soak it in a commercial solvent for several hours. Soaking it overnight is even better.

Then clean all solvent off with a spray type carb cleaner, making sure to get lots of cleaner into every hole and passage there is. Pay special attention to the tiny holes in the bore of the carb, under the throttle plate for the carbs that have these holes. Use lots of cleaner. And make sure to wear safety goggles to avoid getting the over spray into your eyes. There will be over spray.

Dry the carb with low pressure compressed air.

There is no rebuild kit for this carb, as it is a sealed unit. These EPA compliant carbs are not meant to be taken apart at all, although you can sometimes clean them.

Occasionally, even a good cleaning is not going to be sufficient, and you may end up having to replace the carb anyhow. Be prepared for this.

Let me know how this turns out.

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$17 : I have an Onan 4 KW gen on my motor home. It starts and sund