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lazygordon's avatar
lazygordon
Explorer
Jul 15, 2017

Onan marquis gold 5500 surges

My onan that I just got with my used rv is having issues. It's an onan marquis gold 5500 model hijab with the old carburetor. It starts and idles fine, but when you put it under load it just sits and surges. The governor just goes up and down. I figured it had sat for awhile and the carb got varnished up. So I pulled the carb and the throat of it shows issues of varnish. I'm going to clean it with some seafoam and see what happens. But now I'm wondering if the carb is varnished would it start and idle ok? So is my surging issue something else? Trying to get as much info as possible if cleaning doesn't work. Thanks for any and all ideas.
  • drmopar's avatar
    drmopar
    Explorer
    Jul 16, 2017
    Normal with old fuel. Add double doses of fuel system cleaners in tank with fresh fuel. Run for a couple of hours, then shut down and let it cool. Double check oil level as well. After a couple of these cycles, it should run fine. Last year I added a double dose of STP gas cleaner and stabilizer. Months later it fired and ran smooth.
  • gbopp's avatar
    gbopp
    Explorer
    Jul 16, 2017
    Change your generator fuel filter and make sure the air filter is clean.
  • garyemunson's avatar
    garyemunson
    Explorer II
    Jul 16, 2017
    Generally, if they are surging, the carburetor is seriously varnished up. There is nothing that you can pour in it that will fix the problem. Dried gasoline varnish is impervious to almost anything. The only thing I have seen in 40 years of working on stuff that REALLY works is Gunk Hydroseal, a pretty expensive shop grade cleaner that separates into a thin top 'sealer' layer and the good, bottom stuff that does the cleaning when you submerge the part in it. Get in on your hands and pay the price. A overnight soak in straight lacquer thinner is second best. Nowadays it's usually better to just get a new carburetor and be done with it.
  • PERCs's avatar
    PERCs
    Explorer
    Jul 16, 2017
    Actually...SeaFoam does work. Been using it for years on various engines I pick up with this problem.

    David
  • lazygordon's avatar
    lazygordon
    Explorer
    Jul 16, 2017
    Thanks for all the ideas. Just got done tearing down the carb and gave it a good cleaning, all passages seem open and clear now. Cleaned up most of the varnish in areas that could effect flow of fuel. I'll post how it works if it does when I get a chance to put it back together and try it. Thanks again for your ideas.

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