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Generac 4000xl series model number 09777-1. New fuel, line…

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Generac 4000xl series model...

Generac 4000xl series model number 09777-1. New fuel, line checked all the way through to carburetor, bowl full of fuel, oil level checked and added to, engine cranks runs great for about 30 seconds and stops

Mechanic's Assistant: Can you guesstimate how old the engine is? And has it done anything like this in the past?

Guessing about 18 years, I do not remember it doing this before. Maybe you can decipher age by serial number(###) ###-####

Mechanic's Assistant: Do you plan on doing the work yourself?

Yes,

Mechanic's Assistant: Anything else we should know to help you best?

I have pulled the carburetor seems pretty clean. Plenty of fuel in the bowl. Oil was low to begin with added new wonder if protection system is hung up due to age?

Submitted: 11 months ago.Category: Small Engine
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Answered in 36 minutes by:
9/9/2017
Technician: Hank F., Technician replied 11 months ago
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 16,001
Experience: Certified on Onan and Generac generators
Verified

Hello, my name is ***** ***** I am going to assist you with this.

It is very doubtful that the oil switch would work for 30 seconds, and then quit. Also, if the oil alert light is not coming on, it shouldn't be the swtich. But if you want to test it, simply unplug the yellow wire from it, and insulate the wire so it can't touch ground.

If the unit keeps running then, you know the switch is bad.

If the oil is full and the switch is good, the most likely issue is a bad carburetor. It is not allowing enough fuel in to keep the engine running.

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.
Today’s gasoline formulation goes bad in as little as 30 days.
This condition is cumulative. Every time gas sits, the varnish builds up just a little more, like coats of paint, until eventually gas can not flow. It will not happen overnight, but the symptoms can show up all of a sudden, even while simply stopping to refill with gas.
The use of fuel additives, such as Sta-Bil or Sea Foam will not stop this process from happening. They will greatly slow it down, but the gas will still go bad.

This can also happen even on a brand new engine or brand new carb. When the carb is built, it is run at the factory to tune it.
After tuning, they do not always get properly cleaned, or may not have enough/any preservative injected. Believe it or not, this is actually fairly common.

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.
If this is the case, you will need to change the oil and filter, if it has a filter.
Varnish can also cause the float needle to stick shut, and not allow any gas to flow from the carb bowl into the engine.

The only 2 solutions are to either replace the carburetor or give it a good, thorough cleaning.
When removing the carb, make sure to take a good picture, or make a good drawing of where all springs and linkages are attached. This will make reassembly much easier.
Most people believe that cleaning a carb involves removing the bowl and wiping it out, then spraying some carb cleaner through it.
This is simply insufficient. It takes months or years for this accumulation to build up – it just can not be removed in minutes.

To properly 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.
When reassembling the carb, make sure to use a carb kit, when one is available for your carb.

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.

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