onan 4k gen

[Rhigley]

my gen. will run without load for about 45 seconds then will hunt 2 times than run smooth again for a 45 more seconds again. When I put a load on it (1500 BTU AC) it will do the same but not as often. I have been exercising it the past few days trouble shooting it.(about 2 hours under load) Any ideas on what to try? Thanks

[Rhigley]

problem salved.....Took the altitude adjustment cap off (just pressed on)counted the turns to closed (1 1/2 turns) then unscrewed needle valve all the way out and drained the bowl and sprayed carb cleaner thru valve body until I had cleaner flowing from drain on bowl. Placed it all back together and turned needle valve 1/4 of a turn more than it was at first..Running like new now with 1500 ac and electric water heater on at same time . Thanks for all your help

[Gdetrailer]

Depending on model and yr, there may not be any mixture adjustment, most newer small engines only have fixed jets with nothing to adjust the mixture so there may or may not be a emissions limiter cap..

Either way, the fix is to remove and clean the jet and if equipped there is a tiny emulsion/mixing tube above the jet which has a bunch of little tiny holes.. It only takes one of those holes to plug to cause hunting..

If no tube then there may be a passage way past the jet clogged..

Not totally familiar with Onan carbs but have worked on a variety of small engine carbs from B&S, Honda and Honda clones and most of them use pretty much the same setup.

[1320Fastback]

This^

Take the California Emissions cap off and richen it until it runs smooth.

[garyemunson]

Try prying off the limiting cap on the altitude adjuster so you can open it a little more. If that cures it, the main jet needs to be cleaned.

[Gdetrailer]

Jets clogging have nothing to do with the overall gen run hrs.

They will clog easily unless you drain the bowl completely and sadly the bowl drains tend to not be at the lowest point of the bowl leaving a small puddle of fuel at the bottom. Removing the bowl effectively dumps out every bit of leftover fuel.

Just had to deal with a clogged jet on a portable 4Kw gen I take camping, was lazy the last time I used a couple of yrs ago, only pulled the drain plug. Left one heck of a mess in the bottom of the bowl this spring and was only able to keep the gen running at half choke. Took two times removing and cleaning jet and tube to get gen to run perfectly without choke.

Just a fact of life.

[Rhigley]

I only have about 60 hours on it. I'll replace fuel filter and see if that dose anything. I know when I prime it a lot of gas is moving because I have had the bowl drain open and the container I use under the bowl fills quick. I'll try to remove the bowl and take a look. Thanks

[Gdetrailer]

Draining bowl can help and it "should" fill back up but the float can stick, the float valve can stick, the fuel pump can be weak, you can have a leak or pinhole in the fuel hose from the vehicle tank.

Draining bowl does not drain all fuel, it will typically leave a small amount in the bottom of the bowl unless you remove the bowl and dump it..

That leftover remaining fuel as it evaporates off tends to attract moisture from the air which often will corrode the fuel bowl.. The corrosion sits on the bottom of the fuel bowl until you fill the bowl and then it gets picked up by the jet and clogs the jet and or passages.

Hunting means you typically have a starvation fuel problem (IE lean condition), if you have a manual choke you can sometimes "correct" lean condition by closing the choke until smooth.. But that is not a real fix, just a bandaid plastered on top of the problem.

You need to find out if you are getting enough fuel from the tank (weak pump or fuel line issues).

If you have good fuel flow then carb cleaning most like is needed.. If I remember correctly, Onan doesn't recommend cleaning the carb, only replacement and they are not cheap and a few models impossible to source.. I would try removing the carb from the engine, breaking it down and remove and clean the jet and passages first if you have plenty of fuel flow from your tank..

On edit, I should note that on some gens the fuel pump may be electric and some are vacuum "pulse" pumps which use the intake vacuum pulses via a rubber diaphragm.. The diaphrams often get softened from the gas, sometimes they get brittle and brake or they may get a pinhole causing the fuel pump to not work correctly..

[Rhigley]

I do drain the bowl when I'm not going to use it for a bit.(like when in storage) The bowl should fill back up.

[Gdetrailer]

Gasoline?

If so, hunting is typically too lean of a mixture which would indicate a plugged carb jet or not enough fuel in the carb bowl.