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10forty2's avatar
10forty2
Explorer
Aug 11, 2014

Onan 5.5K Generator

Having trouble getting my generator to run. I dove into it yesterday and found that apparently it's not getting enough fuel through to the carb. Disconnected the fuel line, removed the fuel filter...it's open, evidenced by being able to blow through it. Some gasoline blew out of it and some runs out of the feed line, but not what I would think would be an adequate amount. The unit acts like it wants to catch and start running on its own, but it quickly stops when I let off the starter switch. I removed the spark plug, grounded it and hit the starter...good spark, so that's not the problem. I removed the breather and injected a small amount of gasoline directly into the carb and for a few seconds, it runs. Which tells me I have air and spark, but not enough fuel.

So....before I tear into the carb to check for a stuck needle or float, is there a separate fuel pump for the unit or is it simply a vacuum feed? I do not have documentation on it that came with the coach, and can't seem to find any documentation specific to my unit online.

13 Replies

  • I would suggest checking the rubber gas line for any signs of old age, crackng, etc. If you are lucky enough to inspect all the way to the tank connection look for any leakage. I would suggest disconnecting at the generator and and hook up a new line and run it to a 5 gallon gas can to check if the unit will run, that will eliminate any gas line problems as far as a faulty line to the tank.
  • It is a gasoline unit that gets fuel from the main gas tank for the drive engine. I'll get the data plate information and go from there.
  • Doug,

    There are three different Onan 5.5 units.
    It probably did have a fuel pump - I'll get back to that.
    Without knowing the model and the age, that is a stopper.
    I am guessing that it is a gas engine because it has spark plugs, but some of the Onan 5.5s are diesel and some are LP.

    Collect the data plate and search the web, there is probably a manual -service or at least operators - available somewhere.

    If the unit is more than 10yo, replace all the fuel lines and then test the fuel pump. There probably is one, but it may have been murdered by the alcohol that the put in what is now sold as motor fuel.

    I have had to deal with this on all of my old generators.

    Matt