I have the gasoline Onan 5500 Marquis BGM series with the altitude adjustment on the bottom of the carburetor fuel bowl. I posted a while back about my genset not running. It wold turn over fine, but would never catch and run without me physically holding the choke butterfly closed. I had eliminated spark plug, oil level, fuel lines, fuel filter, air filter and gasoline level in the tank and came to the conclusion that the carb was gummed up from non-usage by the prior owners.
After reading multiple times that Onan carbs are not supposed to be serviceable and shoudl only be replaced for about $300, I ran across one posting online where an Onan mechanic had stated how to gain access to remove the fuel bowl. The black altitude adjuster is removable by using a pair of pliers and some moderate downward force. The button just pulls right off without damaging it. Once it is off, the needle valve assembly secures the bowl and can be removed with a standard .5" wrench.
After removing the needle valve and bowl, I quickly discovered that my assumption was correct...the bowl was full of old gasoline varnish and the needles valve was mostly stopped up. The float was stuck closed too. I soaked the bowl and needle valve in Sea Foam for about 30 minutes and amazingly, most of the varnish dissolved. I used a small, stiff wire brush and scrubbed the remaining varnish from the inside of the fuel bowl and soaked it again in fresh Sea Foam. I gently worked the float back and forth to free it and using a stiff nylon brush soaked in Sea Foam with a gentle touch, I was able to clean the float hinge to where it moved freely up and down to work the float valve properly.
After marking the location of the adjuster for the needle valve, I carefully unscrewed it from the orifice and counted the number of turns it took so I could reinsert it to the original adjustment. It too, was pretty gummed up as was the orifices through which gasoline is sucked up past the needle into the carburetor jet. Once removed, I also soaked that assembly in Sea Foam and lightly scrubbed it against the wire brush to remove the varnish deposits. Another soaking, another brushing, and then several blasts with Gunk brand carburetor cleaner for good measure, the parts were clean. Using a small cosmetic mirror from my wife's makeup drawer
๐ (I'm sure I'll hear about that later), I also carefully shot some carb cleaner into/through the jet inside the carburetor from underneath without removing it. I never saw any varnish there.
After all was cleaned and reassembled, a touch of the start button and the genset cranked over several times before picking up it's prime and BAM...... it started running! A little rough at first as it cleared all the pure carb cleaner and Sea Foam, but once it picked up some good gasoline, it purred like a kitten!! After about 10 minutes of running smoothly, I loaded the generator a little at a time by first turning all the lights on in the coach, next the refrigerator, and then finally both A/C units. It surged slightly when the A/C units' compressors kicked in, but continued to purr steadily for the next hour as I let it run! I unloaded it and let it run for another 30 minutes or so without problems.
WooHoo!! Problem solved for a couple hours worth of time sitting in the driveway tinkering and about $20 worth of Sea Foam, carb cleaner and small wire brushes. Sorry for the long post, but after searching and searching online and only finding the one post about repairing the Onan carburetor instead of replacing it, I figured someone else might benefit from my trial and success!! For reference too, I did find an aftermarket place that has prett good prices on Onan parts as well:
http://www.partsfortechs.com/asapcart/generator-parts-onan-c-14_104.htmlI sincerely hope this helps someone in their quest to repair their generator!!
1999 Holiday Rambler Endeavor, 36' Gasser
Triton V10, Ford F53 Chassis
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