Onan 4KW starting issues

[two_travelers]

Our 2014 Newmar Baystar has the 4KW gas Onan generator. I find that starting it after it sits for a few weeks is difficult. It turns over readily, but won't catch. I find that primeing it helps. Is this normal. Our previous 2008 coach had no such problems. I wonder if it where they placed the fuel line.

[Gjac]

Snowman9000 wrote:
We took delivery of our RV within days of it coming off the assembly line. The genset has started hard from day one. I'm convinced they are leaned out too much.

The altitude adjustment is on the main jet, so I have read. I wonder if it can be altered.

You can adjust the jets and that helps but I think the main problem is that the fuel drains out of the fuel line back into the main tank after sitting for a while. I put a clear plastic fuel filter when I changed it last time and I can see it go from full to empty after several weeks of sitting. It takes 3 tries to get the fuel pumped out of the tank to the carb to start it.

[Snowman9000]

We took delivery of our RV within days of it coming off the assembly line. The genset has started hard from day one. I'm convinced they are leaned out too much.

The altitude adjustment is on the main jet, so I have read. I wonder if it can be altered.

[Mike_Hohnstein]

My Onan has 300 hrs, always been a pain, gone to using starting fluid, fires right up, I hate it so much I don't care.

[Lumpty]

Regular exercising of the generator will go a long way to keeping it running well and starting easily. As said, the stop side of the start rocker switch is also how to prime the carburetor. My Onan 4kw can be a bit fussy to start. Today it was monthly exercise time, and it took 3x of cranking until it fired. It hit 637 hours today, in 4 years and 4 months of owning the RV since new, running so far without issue just requiring regular maintenance.

[Gjac]

I do something similar to Wes's suggestion. I use a gal of gas and 8 oz of Seafoam and run the generator under full load for an hr to exercise it and clean the carb at the same time.

[garyemunson]

I've found quite a few people haven't read their manual and don't know you hold the 'stop' button down until the display comes on. This runs the electric fuel pump to prime the carburetor before pushing the 'start' button. Also, Onans have a drain valve on the bottom of the carburetor bowl (no, it's not an adjustment valve). Use a small cup to catch the drained gasoline. Also keep in mind the 'top tier' gasoline specs require fuel stabilization be included that makes fuel good for one year (no need for Stabil). Note this does not negate the need to drain a float bowl as dried up gasoline still leaves a hard deposit that will close up the precision jet hole in the carb and cause a lean condition that makes hard starting and a 'surging' running. If you are following proper priming procedure and the unit still starts hard, most likely that jet in the float bowl dip tube is undersize from said deposits. It's possible to carefully clean these. CAREFULLY using a welding torch tip cleaning tool works but just replacing the carb is probably the easiest strategy for most people.

[Cloud_Dancer]

The carburetor and fuel system that's in question is flawed,....IMO.
The other thing is that some owners do NOT understand where and why the system is flawed.
Be aware that whenever the gasoline that's inside the carburetor is allowed to remain in the carburetor, after shut-down, the gasoline dries out and residue, gummmy-varnish STUFF is left behind such that it messes up the ability of the carburetor to perform.
IF you solve the problem by installing a manual fuel valve, it's absolutely important to know why this is done, and to know the proper procedure of shutting down the generator. Know that the main purpose of the valve is to force the generator engine to suck ALL the gasoline out of the carburetor, as the new way to shut down the generator. Of course, to make all this work, you must start out with either a new carburetor, or one that has been taken apart and properly degummed.

[Snowman9000]

two travelers wrote:
How long do you hold the prime switch on for? Is there a danger of flooding if held too long?

No danger of flooding. It's not that type of priming. It just activates the fuel pump to make sure the carb is full. When it is full, the fuel pump keeps running but not pumping more fuel.

[shawdowboss]

A good 30 secs with the prime button if its not been run for a while. After the winter, i go 45 secs. Both are after the clicking stops which means the fuel is running.

[two_travelers]

How long do you hold the prime switch on for? Is there a danger of flooding if held too long?

[fortytwo]

It's the nature of the beast. Asked the Onan Rep at the FMCA Rally in Madison, WI last summer. His fuzzy answer confirmed my conclusion that the Onan 4K carb system is a POS, and deliberately not changed to insure a revenue stream for new carbs. They consciously do not make replacement parts. If you let one set 6 months without starting plan on a new carb. I told him that expecting the old farts who own these things to start them up every 30 days was head-in-the-sand thinking. I gathered from our conversation that they won't fix it as the engine part is not made by Onan but is actually a Kuboto engine.

A shut off will help (will be putting one on the 4KW in my new MH). Unless I prime it takes 3-4 crank sequences to start. Using a shut-off and running it dry will help in hot weather. I'm considering having a "T" adaptor with outboard motor type connection. Running a small tank of half fuel-half gumout was an old marine dealer solution to fixing outboards (with tiny carb jets) that sat over the winter. Never had trouble with my outboards in the spring after learning that.

[Chum_lee]

My 1999 Onan 4KW genny @ 1300 hours on the clock does the same thing. If it sits for more than a few days it takes about 8 to 10 seconds of cranking to fire up. If is sits for one day or less it starts after 1 to 2 seconds of cranking and runs fine.

I don't know if the newer Onan gennys still have an altitude compensating screw on the carburetor, but, if you have one, you might want to check to see if its set to your approximate current elevation . . . . . +-1000 feet.

Chum lee

[Gjac]

I don't have a prime on mine so it takes me 3 tries to get it started. So yes this is normal. I think installing a one way valve would prevent the fuel from draining back into the tank making it easier to start because the fuel would stay in the line.

[fourmat]

Effy wrote:
Yes this is normal. If it's been sitting more than a week I often prime it 2x and it starts right up. I could get away with priming it once but then it sits there and churns away trying to start. Hit the prime again and it starts immediately. If it's only been a day usually you don't have to prime it at all.

same here 2 primes if its been sitting and it fires right up