Onan microlite 2800 Gas Carburetors

jltarley wrote:
I've recently purchased a 1988 RV with an Onan KV spec J 2.8 gasoline. I was able to get the generator running, but it runs rough, and surges very strongly. All research leads me to believe that the carb needs replaced.

The carb in the generator is P# 146-0861. I've had a hard time finding a replacement for less than $300, and there just does not seem to be a lot of them out there. I have been able to find quite a few 146-0569 carbs, which are from previous versions of the same model gen.

Are these carburetors interchangeable? If not, does anyone have any other good solutions for this issue?

There is most likely no "direct fit" carb available, some like Onan are proprietary to that manufacturer.

Now, if you are extremely handy with wrenches, have a good shop full of metal working tools like lathes and milling equipment it might be possible to "fab" your own adapter to a small engine carb like a Honda.

Then the problem there is figuring out how fuel gets to the carb, is it compatible with the fuel pump used, the linkages work, getting the throttle to work with the governor and the proper RPM of the engine.

Now, about this time your are thinking that all is lost..

Perhaps, you should think about trying to CLEAN the carb first before declaring it dead..

Many small engine carbs use a similar setup which uses what is called a "jet", the jet meters the fuel that is taken into the carb throat.. The jet gets clogged and now the engine may run ruff or not at all..

Many small engine carbs you can remove the fuel bowl and access the jet to clean it with spray carb cleaner.

See PAGE 3 IN THIS LINK where I tell how this can be done on a Honda GX series carb which might be helpful to you to figure out if the Onan carb can be serviced.. There is a link to some You Tube vids that may prove helpful..

If your Onan carb has similar design, you might be able to disassemble and clean the jet for the price of your time and a can of carb cleaner..

I hate this "throw away" mentality that is prevalent now days..

If you can get the carburetor off then soak it in SEAFOAM for 24 - 48 hours or a quality carb cleaner.
Retry

Seafoam may or may not "work" but it should not cause harm..

The problem is that just sitting the carb in a vat of any cleaner including Seafoam often will never make it to where the clog is..

The gas could be treated with some Seafoam and allowed to run then shut down for a day or two between runs might help clear a partial obstruction but will not help at all for a full obstruction..

Now, to complicate things abit, there are two types of carbs, gravity fed (tank above) and fuel pump fed (tank below carb).

The link I gave assumes gravity fed, Onans due to the fact that most pull fuel from a tank lower than the carb often will use a fuel pump..

Sometimes the fuel pump is built into the carb operated by the vacuum created by the air moving through the carb body.. Many Briggs engines use that and they call it "pulsa jet".. With that there is a fuel pump diaphragm built into the carb that over time wears out or hardens..

Onan may or may not use that, if they do, unless there is aftermarket manufacturers making that diaphragm you are out of luck..

If Onan is using a external vacuum diaphragm pump (separate pump with a vacuum hose that goes to carb vac port), you may be able to find replacement pumps..

Some may use an electric fuel pump which may be possible to substitute with a low pressure aftermarket auto fuel pump designed for old school carburetors (not fuel injection).

The reason I brought this up is if the fuel pump is weak, your carb may be running out of fuel and hunting causing your symptoms..

But a good cleaning of your carb should not cause problems and is a logical step to trouble shooting instead of simply replacing parts..

Soak in Seafoam.
Retry.
Report back.
Also as a back up call Cummins/Onan parts and ask the question on your carb. Last time I needed a part they beat the retailer by $5.00 on a $40.00 item

I serviced small engines for a decade. This is the most effective way to clean a carburetor: Remove carb from engine (make note of connecting throttle and governor rods/springs). Place rags on clean work surface and disassemble carb, including fuel adjustment jets and any plastic. Place parts in a line on work surface in order removed. Sometimes, the adjustment jets can be run in all the way to calibrate for assembly, later (be careful, don't bend anything). Place all the metal parts, including the carb body, in the basket of the carb cleaner container. Lower the basket into the cleaner and let soak. A few hours is usually good. Overnight, all residue is softened. Clean parts with solvent or gas. Blow dry. Reassemble.

I am still using my original gallon container of Berryman's carb cleaner, purchased 15 yrs ago. I have cleaned over 100 carbs with this cleaner.

Good luck!

Just out of curiosity, does it run rough/surge with no load, under load or both?

marcsbigfoot20b27 wrote:
Just out of curiosity, does it run rough/surge with no load, under load or both?

Both.

Lazy man's method of cleaning carb: Remove fuel line from pump or tank. Let the fuel run out of fuel line. Fill fuel line with fuel line cleaner or other solvent. Reattach fuel line. Turn over engine until cleaner runs through carb. Let sit overnight.

Very lazy man's method: Pour large amount of fuel line cleaner or solvent in tank with small amount of gas. Run engine until cleaner is through carb. Let sit overnight.

westend wrote:
I serviced small engines for a decade. This is the most effective way to clean a carburetor: Remove carb from engine (make note of connecting throttle and governor rods/springs). Place rags on clean work surface and disassemble carb, including fuel adjustment jets and any plastic. Place parts in a line on work surface in order removed. Sometimes, the adjustment jets can be run in all the way to calibrate for assembly, later (be careful, don't bend anything). Place all the metal parts, including the carb body, in the basket of the carb cleaner container. Lower the basket into the cleaner and let soak. A few hours is usually good. Overnight, all residue is softened. Clean parts with solvent or gas. Blow dry. Reassemble.

I am still using my original gallon container of Berryman's carb cleaner, purchased 15 yrs ago. I have cleaned over 100 carbs with this cleaner.

Good luck!

Correct.

Which is why I mention just sitting the carb in a solvent bath does nothing..

The main area the build up affects is at the main jet and atomizer tube, very fine small holes that could take weeks, months or even years before a solvent will ever make it through without PRESSURE or even cleaning wires..

To make the solvent work, the carb does need to be dismantled in order to get the solvent into all the areas..

Then once the solvent has had time to soften the deposits you need to thoroughly remove the offending build up with either air pressure or spray cleaner..

Then careful reassembly after that..

That is why many manufacturers like Onan specifically tell their techs to replace the carb.. Simple and effective but costs the owner an arm and leg..

westend's method x2

Back in the days of "Hell No We Won't Go" I was stuck rebuilding carburetors. I had a 5-gallon pail of extremely obnoxious smelling carburetor "dip" and a basket.

An overnight "dip" followed by an immersion in boiling hot rinse water did what it could. I had an "unapproved" full force rubber-tipped blow gun operating at 140 PSI.

Even with all that, I had some quadra-jets and later on, thermoquads who resisted to the last - took full force 140 psi air, then "ptuuii" something spit out of a passage or orifice.

I can only wonder at the efficacy of soaking something in mouse-milk.