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I have a 7NHMFA26106C generator on our 1992 fleetwood coronado.

Customer Question
it runs but surges most...
i have a 7NHMFA26106C generator on our 1992 fleetwood coronado. it runs but surges most of the time. periodically it will not surge but then starts surging again. took it to a local onan service center and they could not detect problem - advised to to take to cummins shop a couple hours away - any thoughts
Submitted: 2 years ago.Category: RV
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Answered in 12 hours by:
6/25/2015
RV Mechanic: Hank F., RV tech - emphasis on gensets replied 2 years ago
Hank F.
Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 15,729
Experience: RV tech since the beginning of the millenium.
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Hello!
My name is ***** ***** I am going to assist you with this.
This is a classic symptom of a carburetor that has become plugged with varnish.
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.
If for some odd reason this does not help, please let me know so I can assist you further.
.
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RV Mechanic: Hank F., RV tech - emphasis on gensets replied 2 years ago
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Customer reply replied 2 years ago
kind of - wondered what other causes it might be. We decided to replace carb. to get the top plate off our gen you have to lower the whole generator down because the generator enclosure covers the side panels where you have to get screws out.
My husband had noticed that they seal between carb and air filter area also has a chunk out of it. Hopefully replacing carb and seal fixes it.
RV Mechanic: Hank F., RV tech - emphasis on gensets replied 2 years ago
Surging is caused by a lean condition - too little fuel, or too much air.
The seal between the air filter and carb is not going to be the problem. An air leak would have to be after the carb, not before. And unless you have had something apart and tore a gasket, there will not be an air leak.
Yes, that top cover on an NHM is in the way, and often removing the top cover requires dropping the genset.
Thank you for using Just Answer, and please don't forget to leave me an appropriate rating.
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Hank F.
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