gnxtc2
USA
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Joined: 03/22/2012
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I bought a used GN trailer. The trailer came with a 7000w Onan Marquis gen set, model # 7NHMFA26105H with 53 hours on it. Prior to me buying the trailer, it sat atleast 5-6yrs. The fuel line to the carb on the generator was pulled and the carb was ran dry but they left the fuel tank 1/2 full.
I removed the fuel tank and dumped the fuel. I sent out the fuel tank to get "boiled" and coated. Put everything back, put fresh fuel and it crank over but wouldn't start. Found that the electric fuel pump was siezed. Ran to the Onan/Cummins store and bought a new fuel pump and fuel filter. Replaced them and the generator fired and was running.
I turn on the three interior fluorescent lights and all is well. The trailer has 2 - 500w quartz lights on the passenger side, 2 - 500w quartz lights for loading and another 2 - 500w quarts lights on the driver side. There are three switches controlling each pair of lights.
Leaving the interior lights on I start turning on the quartz lights. I start with the passenger side all is fine. Next are the loading lights, the generator starts to surge. Finally I turn on the driver side lights, the generator is really surging to the point of almost stalling out.
I turn off all the quartz lights and the generator is running fine. Next I turn on the air compressor, as soon as the compressor turns on, the generator shuts off instantly. The air compressor is a 20 gal, 5HP oil less Craftsman. I plug the air compressor into the extension cord and it runs fine.
I bought the service, parts and owners manual for the generator and there is nothing about the issue I'm having. The trailer was built with everything I mentioned, nothing was added over the years. So I know it worked when it was built.
Where do I start to find out where my problem is? Do I need to replace the carb. Would it be noticable if the generator is only running on one cylinder (it has two cylinders)
Billy T.
gnxtc2@aol.com
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rk911
Wheaton IL
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Joined: 05/30/2004
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no expert here but...a 7000-watt genny at a nominal 120-volts AC can supply 58-amps of power. how many amps does each light pull? i can't believe that your lights pull as much power as some smaller homes but it'd be good to know for sure.
start the genny and using a volt meter measure the voltage at one of the outlets. nominal voltage is 120-volts. low voltage requires more amps to power appliances. if you find low voltage you may have a bad voltage regulator. have you inspected the spark plug?
73,
rich, n9dko
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kneal44
EAST CENTRAL TEXAS
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under modest load you maybe fuel starved.
test: when surging spray some engine starter.. if surging continues then you may have too much fuel going to engine.
if surging stops as you spray then u are fuel starved... the carb needs cleaning and adjusted so you can get more fuel into engine under load.
let me know how that works.
when u play in the sand .... you can get stuck
9-24-08 corpus christi padre island texas. wrecker had to haul me out!
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TEXAS
Centerville Tx
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Joined: 08/17/2003
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First make sure it is running on both cylinders. They can run on one fairly smooth and carry part of a load. You also need to check the voltage and hertz with a meter. Should be around 125 at 62 Hertz or cycles as some call it no load.If you think it could be a carb issue. Put some sea foam in a gas can and let it run off of the gas sea foam mixture for awhile.
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allen rvtech
chilliwack bc
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Joined: 03/28/2012
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you have to have a fluke meter to keep up to hertz on an onan ,do not manually spike the throttle on the genset unless the breakers are off ,or else the frequency will change and burn out electronic boards.revving up the genset will give a code of overfrequency and shut itself down.if your start switch has a flashing light then a code has been set,press the start button three times fast and it will give the codes
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MEXICOWANDERER
las peñas, michoacan, mexico
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allen rv tech,
Years ago I was always afraid to droop Hz to 55 or below or 65 or above because of issues re: voltage regulator. Boy how times change!
Also it would do no harm whatsoever to add Chevron TECHRON to the fuel supply in the maximum dose as suggested by Chevron. Carbon deposits on engine internals have caused symptoms I do not care to relate. Run the engine at max load threshold that starts to cause surging and see if the Techron improves things. Techron cleans out carbon like nothing else I have ever encountered.
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RGordon
Atoka, TN/North Ft Myers, FL
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My 5500 Onan did the same thing and was caused by not running unit enough. Tried to clean the carburetor couple times to no avail. Finally found a new one on ebay for $175 and installed, ran perfect. The carburetor will gum up in the jets even if it was ran dry, something called residue. Mine would run perfect and the more load you added the more it would sputter, then finally die. The jets are impossible to get clean without removing it and soaking. It actually starts better now than it did new with the new carburetor.
Ron & Libby Gordon
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Kamphiker
South Florida (this 'aint paradise anymore)
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Joined: 07/09/2002
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I would start by running Seafoam Motor treatment thru the Genny to clean out the gum buildup in the carb.
2006 Winnebago Outlook WF324V
2009 Honda CR-V 2wd TOAD ......Campgrounds in the Smoky Mountains NP
Last Camping trip ->2011 SUMMER SMOKY MOUNTAINS NATIONAL PARK
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TEXAS
Centerville Tx
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Joined: 08/17/2003
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Never rev it up by hand. Seen that done to many times. Makes the magic smoke come out. Then leaves you with a high repair bill.
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gnxtc2
USA
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Joined: 03/22/2012
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Had to replace the carb. My luck it was an emission carb and it cost me around $320. Replaced the carb and no more surging.
Now I have another issue. Started a new thread on it.
Thanks
Billy T.
gnxtc2@aol.com
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