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-   -   Typical Class C generator fuel prime time? (https://www.irv2.com/forums/f87/typical-class-c-generator-fuel-prime-time-533893.html)

THenne1713 04-30-2021 11:39 PM

TandW: Newer models of ONAN (Such as KY Microlite) run the FP to Prime if you hold STOP; (Also gives Fail CODES thru flashing lights at the START buttton, LOL) Pressing STOP latches the IGN Kill without holding, but Holding STOP Runs fuel pump; older, (such as My 22-yo Emerald Plus) give NO codes and have NO Prime. Hope this helps

RV2009 05-12-2021 08:02 AM

Quote:

Originally Posted by cobia6620 (Post 5723913)
I have an 11 year old 31 ft Fleetwood Class C with 115 hours on the generator. Every month I run the generator for 1-2 hours under load and during the past year or so the time to prime the fuel system in order to start has increased to 1-1.5 minutes. After starting it ran fine. This week I installed a new fuel pump and filter and now the prime time, after sitting a few days, is 14 seconds. What is typical fuel prime time for a long class C ? I have a full fuel tank and religiously use fuel treatment. The fuel line back to the tank from the generator seems good as the new fuel pump had a steady flow when disconnected from the carb.

I just checked. Our Onan Generator is now 20 years old, has 730 hours on it.

Never had to prime it, 3 to 5 second cranks always fires it up.
Never ran it as recommended by the manufacturer, with the recommended load. Just run it maybe 1 hour every other month with A/C on.
Never winterized it.

Sometimes it is not used for 3 months at a time.

But: Every 2 years it gets new air filter/spark plug and oil. Thus the manual states that some of it is not even due yet.

THenne1713 05-13-2021 07:13 PM

My 21-yo Onan 4k Emerald Plus has no prime function like later models and starts/ runs usually after 3-second crank, 3-sec pause, and 2nd crank usually starts immediately

THenne1713 05-15-2021 10:45 AM

Maybe not on paper, but setup PC folder and download most all manuals and literature to ONE folder; you can do sub-folders for Onan, Dometic, etc... Include your Onan OWNER and Service Manuals. You can then backup all w/ 1-click to a Flashdrive or other device?

twinboat 05-15-2021 11:05 AM

How long it takes to prime ( fill the carb bowl ) , depends on outside conditions, and length of time between runs.

The gas in the bowl is evaporating, when not being run.
The hotter it is and the longer it sits are both factors in the evaporation rate.

The carb bowl doesn't need to be full for the engine to start, but if to low, it will stall out before the bowl refills.

The choke setting comes into play too. If set lean, you will need more cranking time.

Bill Gail 05-15-2021 08:51 PM

Quote:

Originally Posted by craigav (Post 5724250)
I certainly agree, I stated 3 seconds of the stop button but it could have been 5, so 3~5 seconds, and another thought as I had edited one of my replies earlier, the fuel pump on mine makes a clicking sound (likely they all do) which makes me think perhaps the pump doesn't have a rotating motor, maybe it has a solenoid plunger type of pump (not sure what they would call it).

Anyway, I will add a thought, while I don't know if all the Onan's have a primer option or not, I would highly consider making a simple mod if mine didn't have a remote primer and that would be to install a momentary switch next to the remote start switch so I could momentarily turn on the fuel pump for 15~30 seconds prior to trying to start the generator if it hasn't ran in a while. As TwinBoat mentioned, running the starter over and over unnecessarily and for an extended duration each time is a starter killer, and one that could be avoided. I never run my starter for more than 5 seconds anymore, because running it longer than that isn't needed.


I think putting in a momentary switch to prime the pump on our 20 y.o. 4000 Onan is a brilliant idea.

I don't have a schematic , but I assume the fuel pump power feeder comes off the generator starter solenoid.

If I connect at that point with the momentary switch is there any chance of back feeding the solenoid and causing damage?

Just don't want to create a problem where there wasn't one beforehand.

Thanks for the help.

THenne1713 05-16-2021 01:22 PM

You are correct on the Onan sliding piston fuel pump, check valve at both Inlet/Outlet (I cut my old one apart)

craigav 05-16-2021 02:06 PM

Quote:

Originally Posted by Bill Gail (Post 5752761)
I think putting in a momentary switch to prime the pump on our 20 y.o. 4000 Onan is a brilliant idea.

I don't have a schematic , but I assume the fuel pump power feeder comes off the generator starter solenoid.

If I connect at that point with the momentary switch is there any chance of back feeding the solenoid and causing damage?

Just don't want to create a problem where there wasn't one beforehand.

Thanks for the help.

I don't have a shematic for the earlier Onans so I am not sure, however I do have one for my model and the fuel pump power line is connected into the generator's control board. With that in mind, I likely wouldn't want to add power to the pump without first disconnecting the power line to the pump that comes from the generator control board. In other words, a center off, double pole double throw switch which would disconnect the 12v power into the pump from the generator and instead connect it to the battery power. It isn't all that difficult, but if I wasn't having any issues and wasn't familiar with what I am saying, I would just keep it the way it is. ~CA

R_2ndWind 05-21-2021 07:23 PM

Quote:

Originally Posted by twinboat (Post 5725932)
Gasoline evaporates from the carburator bowl in 2 to 3 weeks, so its basicly out of gas.
That's why you prime it.

Thanks for that knowledge TB. I always found I needed to prime (hold Stop for a slow count of 10) if it sits for a couple weeks. I kind of thought maybe the fuel syphoned back into the tank or something. Guess it was "or something".


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