Forum Discussion

Steve92004's avatar
Steve92004
Explorer
Nov 08, 2018

Onan 4000 Microliite Carb Spewing Gas from Air Filter

Hi everybody
I had a surging issue with my Onan 4000 Microlite (800 hours)
I would clean the carb and sometimes it would fix it and sometimes not
So I bought a new Amazon Carb, Fuel Pump and Fuel Filter
I put it all in and the generator started right up and ran perfect.
Then I turned it off after a bit to see if it would restart and it wouldn't.
I was troubleshooting and removed the air filter and gas poured out of it and when I cranked it over gas was spraying out of the filter side of the carb
I had put in a fuel cut off valve during the install so I shut off the fuel and tried again and the genny started right up
I opened up the fuel valve and it kept running perfect but when I shut it off and tried to restart, gas was spraying out of the intake again and it wouldn't start unless I shutoff the fuel valve.

Do you think the fuel pump is pumping too much fuel or do you think the carb is defective?

Thanks!
  • CloudDriver's avatar
    CloudDriver
    Explorer
    Nov 08, 2018
    Sounds like a carburetor float with a leak. The float fills with gas and sinks, allowing the float valve to stay open resulting in the carburetor bowl overflowing.
  • Steve92004's avatar
    Steve92004
    Explorer
    Nov 08, 2018
    CloudDriver wrote:
    Sounds like a carburetor float with a leak. The float fills with gas and sinks, allowing the float valve to stay open resulting in the carburetor bowl overflowing.


    That makes sense right there
  • 2manytoyz's avatar
    2manytoyz
    Explorer
    Nov 08, 2018
    Yep, sounds like a float issue. Had the same thing happen on other small engines. I never had a float with a leak, but did have a dirty needle and seat. When the float would rise, it couldn't completely shut off the fuel, and would slowly overfill the carb.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Nov 08, 2018
    You may have a problem that I have run into with replacement carburetors for Onan. If you did not buy it for the direct model number, but for the basic engine type, that may be the problem. Many Onans are run with a gravity fuel feed (squat for pressure) and so have huge opening in the needle seat. This means that almost any pump will over power the float system.

    I don't what you can do if this is the case, because I had to rework that seat to a smaller port size.

    If the pump you got delivers more than a couple of PSI, that can do it. Check the information for that pump. Low pressure pumps are available, but you have look for them.

    Good Luck

    Matt
  • Steve92004's avatar
    Steve92004
    Explorer
    Nov 08, 2018
    Thanks guys
    I pulled the float bowl, the float was fine and not full of gas
    I didn't like how far up the float traveled so I swapped it with my original Onan float and needle. Now it shuts off the fuel to the carb when the float is about level
    I started it a couple times and didn't notice any excess fuel spraying out
    So I got it running on a full load right now and going to let it run 30 minutes
    Crossing my fingers
  • Steve92004's avatar
    Steve92004
    Explorer
    Nov 08, 2018
    Still starting great
    Do you guys drain the float bowl after use so it doesn't get gummed up in there?
    That's the reason I put the fuel shut off valve on there so I could run it empty like I do on my dirt bikes and things that don't get used daily>
    But when I saw how much came out when I removed the float bowl I'm thinking there's still enough in there to gum up the altitude needle at the bottom
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Nov 09, 2018
    Steve,

    You have that figured out and yes, drain it the best you can and then leave it alone. If it is going to be six months or more, fog the engine.

    I have always drained mine (a way older Onan) by disconnecting the fuel pump. When it has stopped and been shut down, then I loosen the hex on the bottom of the float bowl and get just a little more fuel out. Been doing this for over a decade just for this and way longer for other engines in my care.

    Matt

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,188 PostsLatest Activity: Jan 17, 2025