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Thread: Onan 5500 Problems

  1. Print this Post   #1

    Onan 5500 Problems

    Hey guys,
    Figured I'd better fire up the generator before our big outing this week. Wouldn't you know it, it won't run.

    I put fuel in the tank until it was about 3/4 full. I read somewhere that the generator won't run if it is below 1/4 tank, so that was the first move. So she's got fuel in the tank.
    I pulled the fuel line off at the carb and it will pump fuel out the end if I hold the "Prime" button down. So fuel is coming out of the end of the line.
    I read that these carbs can be notorious for getting gunked up, so I pulled it off, took the filter off, removed the small elbow at the filter, took the float bowl off and emptied an entire can of carb cleaner on the thing trying to un-gunk it. I also assured that the fuel filter was clean by blowing through it, it flows very easy and you can blow through it with no pressure at all. Then I put the carb back together and put the happy little clam back on the generator.

    So here's where I am. I can get fuel to pump out the end of the line using the "Prime" button. It's not a lot, but it's flowing. I don't know how "fast" it should pump. If I hook the fuel line up to the carb, open the little screw at the bottom of the fuel bowl and hold the "Prime" button, it will not flow fuel out of the bottom of the bowl. It is like it is simply NOT filling the float bowl with fuel. Now, I'm not a certified mechanic, but I know my way around a small block Chevy. Using my limited mental abilities, my assessment is that the little needle that open the float bowl inlet is simply stuck. I have no clue how to pull that apart to un-stuck it. I tried the "beat on the side of the bowl with a wrench" trick, to no avail. Is there a way to get at that, or is that one of those "just buy a new carb" deals? I see there are no replacement parts for these carbs, just just have to replace the whole **** thing. Is that were I am here?

    Also, I can make the generator run fine on starter fluid, so I know it will run.

    2003 Dodge Ram 2500 5.9L Diesel
    2008 Heartland Cyclone 4012
    Couple Harleys for once the wife & I get parked.

  2. Print this Post   #2

    Re: Onan 5500 Problems

    Quote Originally Posted by TerribleTim68 View Post
    Hey guys,
    Figured I'd better fire up the generator before our big outing this week. Wouldn't you know it, it won't run.

    I put fuel in the tank until it was about 3/4 full. I read somewhere that the generator won't run if it is below 1/4 tank, so that was the first move. So she's got fuel in the tank.
    I pulled the fuel line off at the carb and it will pump fuel out the end if I hold the "Prime" button down. So fuel is coming out of the end of the line.
    I read that these carbs can be notorious for getting gunked up, so I pulled it off, took the filter off, removed the small elbow at the filter, took the float bowl off and emptied an entire can of carb cleaner on the thing trying to un-gunk it. I also assured that the fuel filter was clean by blowing through it, it flows very easy and you can blow through it with no pressure at all. Then I put the carb back together and put the happy little clam back on the generator.

    So here's where I am. I can get fuel to pump out the end of the line using the "Prime" button. It's not a lot, but it's flowing. I don't know how "fast" it should pump. If I hook the fuel line up to the carb, open the little screw at the bottom of the fuel bowl and hold the "Prime" button, it will not flow fuel out of the bottom of the bowl. It is like it is simply NOT filling the float bowl with fuel. Now, I'm not a certified mechanic, but I know my way around a small block Chevy. Using my limited mental abilities, my assessment is that the little needle that open the float bowl inlet is simply stuck. I have no clue how to pull that apart to un-stuck it. I tried the "beat on the side of the bowl with a wrench" trick, to no avail. Is there a way to get at that, or is that one of those "just buy a new carb" deals? I see there are no replacement parts for these carbs, just just have to replace the whole **** thing. Is that were I am here?

    Also, I can make the generator run fine on starter fluid, so I know it will run.
    You were almost to the needle with the bowl off of the carb, there's a small rod that holds the float onto the carb body, you pull that rod/pin and the float comes off with the needle. Clean and reassemble.
    Chris & Sam Albers
    HOC # 5978
    2018 Bighorn Traveler 32RS
    slide toppers
    MORride wet bolt kit
    Eternabond on all roof seams
    2007 Dodge Ram 2500 5.9
    S&B air intake
    Air Lift 5000
    Suncoast Stage 2 Transmission
    Edge Evolution Programmer
    GDP 2 mic fuel filter kit
    Duquoin, Il.

  3. Print this Post   #3

    Re: Onan 5500 Problems

    Thanks Chrisandsama,
    So I finally got it to fill the float bowl with fuel, but it still won't run. I can verify that the "Prmie" button is pumping fuel into the bowl and out the bottom screw at the little drain. So the bowl is full. But it still won't run. I can still make it run for a bit off starting fluid, but as soon as that runs out, it dies. I'm guessing the jets are gunked up? Can those be cleaned? I can't even figure out where they are hiding.

    2003 Dodge Ram 2500 5.9L Diesel
    2008 Heartland Cyclone 4012
    Couple Harleys for once the wife & I get parked.

  4. Print this Post   #4

    Re: Onan 5500 Problems

    The main jet is in the center of the carb. With the bowl removed you can see it, the float is surrounding it. A small flat tip screw driver will unscrew it from the carb for cleaning. Was the bowl full of gunk when first removed? If so the jet probably is also. It should run once cleaned.
    Chris & Sam Albers
    HOC # 5978
    2018 Bighorn Traveler 32RS
    slide toppers
    MORride wet bolt kit
    Eternabond on all roof seams
    2007 Dodge Ram 2500 5.9
    S&B air intake
    Air Lift 5000
    Suncoast Stage 2 Transmission
    Edge Evolution Programmer
    GDP 2 mic fuel filter kit
    Duquoin, Il.

  5. Print this Post   #5

    Re: Onan 5500 Problems

    Yeah, the bowl was stained green on the inside and the fuel was also kind of green colored. Not sure if it had some odd fuel stabilizer that tinted it green, or if it was some sort of algae growing in it.

    The wife pulled rank and ordered a new carb off Amazon, so we'll see what happens when that arrives Tuesday.

    2003 Dodge Ram 2500 5.9L Diesel
    2008 Heartland Cyclone 4012
    Couple Harleys for once the wife & I get parked.

  6. Print this Post   #6

    Re: Onan 5500 Problems

    Quote Originally Posted by TerribleTim68 View Post
    Yeah, the bowl was stained green on the inside and the fuel was also kind of green colored. Not sure if it had some odd fuel stabilizer that tinted it green, or if it was some sort of algae growing in it.

    The wife pulled rank and ordered a new carb off Amazon, so we'll see what happens when that arrives Tuesday.
    The cheap Chinese carbs off Amazon and eBay are a roll of the dice I've gotten good ones and bad ones. Im a small engine mechanic and hopefully it gets you up and going.
    Chris & Sam Albers
    HOC # 5978
    2018 Bighorn Traveler 32RS
    slide toppers
    MORride wet bolt kit
    Eternabond on all roof seams
    2007 Dodge Ram 2500 5.9
    S&B air intake
    Air Lift 5000
    Suncoast Stage 2 Transmission
    Edge Evolution Programmer
    GDP 2 mic fuel filter kit
    Duquoin, Il.

  7. Print this Post   #7
    Senior Member
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    Re: Onan 5500 Problems

    Just remember it takes 3 things for a normal aspirated gas engine to run - fuel, compression, and spark. That being said my guess is you have compression so that leaves fuel and spark. So its easy to check spark so Id go there next.

    Youre probably on the right track being a fuel issue. The problem with the fuel today is left for 2-3 months (could in some instances be even a shorter period) is it gunks up the carburetors internal circuits. Not being there when you say the generator isnt starting is it firing or just cranking over with no hint of fire? If its just cranking Id try spraying ether or carb cleaner into the air filter and see it will try to start. It it starts to fire then in my opinion you probably have an internal carb issue. Not knowing these generators is there a electronic fuel shut off?

    On most of the small engine carbs I have worked is the circuits internally are so small that about the only way to clean them is to remove the welch plugs but finding replacements are next to impossible so replacing the carb is the answer.
    Owners Club #4201
    2018 Oshkosh
    2015 Ram 3500, DRW, Aisin

  8. Print this Post   #8
    Senior Member LBR's Avatar
    Join Date
    May 2016
    Location
    USA - OR
    Posts
    1,100

    Re: Onan 5500 Problems

    Go to YouTube and enter Seafoam Onan Generator and follow the instructions.

    I bought our next to dead generator back to life with a little bit of nurturing.

    It show how to rejuvenate a completely dead genny by mainlining the carb with Seafoam.

    Wished I owned stock in that company....dozens of stories on small engine rehabilitations.

  9. Print this Post   #9

    Re: Onan 5500 Problems

    Quote Originally Posted by RickL View Post
    Just remember it takes 3 things for a normal aspirated gas engine to run - fuel, compression, and spark. That being said my guess is you have compression so that leaves fuel and spark. So its easy to check spark so Id go there next.
    Yup, I know it has spark because like I said below, I can make it run on starter fluid just fine. But as soon as the starter fluid runs out, she dies.
    And I know I'm getting fuel in the float bowl too. I verified that by pulling the bowl off, hooking the fuel line up and running the "Prime" pump while watching fuel pump out the bottom of the carb where the bowl would be.
    So, by my calculations, the issue is in the jets.

    2003 Dodge Ram 2500 5.9L Diesel
    2008 Heartland Cyclone 4012
    Couple Harleys for once the wife & I get parked.

  10. Print this Post   #10
    Junior Member
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    USA - AZ
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    Re: Onan 5500 Problems

    These models are notorious for junking the carbs in the off season, that is how I got mine. My buddy replaced the carb EVERY year for four years and decided to by a portable gen set. I converted the free Onan 5500 to propane (300.00 kit) 5 years ago and have had zero issues since. the carb on your ONAN is not rebuild-able and is expensive to buy, but if you have no other choice I would buy an OEM and take the hit financially instead of eating up you time.


    Good Luck

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