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cobia6620 04-23-2021 10:36 AM

Typical Class C generator fuel prime time?
 
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.

Mudfrog 04-23-2021 10:56 AM

Maybe something different but I only prime our 18 year old Onan 4000 if it has set for a long time. A few days, couple of weeks, no need for priming on ours since the bowl already has fuel in it.

When you said "1 to 1.5 minutes", how do you know? Mine will prime as long as I hold the stop button in. There is no indication that the fuel system is pressured up. If I feel there is a need for prime, I just hold the stop button in for a few seconds after I hear the pump running then release and hit the start button.

TandW 04-23-2021 11:16 AM

Quote:

Originally Posted by Mudfrog (Post 5723936)
Maybe something different but I only prime our 18 year old Onan 4000 if it has set for a long time. A few days, couple of weeks, no need for priming on ours since the bowl already has fuel in it.

When you said "1 to 1.5 minutes", how do you know? Mine will prime as long as I hold the stop button in. There is no indication that the fuel system is pressured up. If I feel there is a need for prime, I just hold the stop button in for a few seconds after I hear the pump running then release and hit the start button.

Prime the O4000 with the stop button? I've been doing it wrong for some 20 years? No wonder it spun out the dried up copper bearings in the starter! I have always pushed the rocker switch to start. And pushed the same rocker switch the other way to stop. But I never, ever got a start on the first push to start. Always had to push to start at least more than once, at five second intervals. and how many times depended on how long since the last run. Fuel evaporates from the bowl and oil leaks all the way down between runs. More so between extended periods. Once a month almost guarantees a start on second try. Your results may differ:popcorn:

craigav 04-23-2021 11:28 AM

The amount of "prime" time for me is like I suspect for others, the longer the generator hasn't ran the longer I need to prime. That equates to no prime time if the unit has ran within the last few days to maybe a minute if it hasn't ran for a month. Keep in mind that the prime (as I understand it for the onan generators) doesn't actually flood the engine or directly inject fuel into it, what it does is simply turns on the fuel pump and once the carb fuel bowl is full, the float inside the carb will stop the flow of anymore fuel.

TandW, check it out, I suspect yours is like everyone else's, just hold the stop button down for about 30 seconds then try starting, if it doesn't start then I hold the stop button down for another 30 seconds. I don't see where any harm would occur (based on my above statement) if one was to prime the generator whether or not priming was actually needed.

TandW 04-23-2021 12:02 PM

Only by holding in the start button does the fuel pump become energized. Check it out in your troubleshooting section of your manual.:popcorn:

GOLDandGREY 04-23-2021 12:11 PM

Quote:

Originally Posted by TandW (Post 5724002)
Only by holding in the start button does the fuel pump become energized. Check it out in your troubleshooting section of your manual.:popcorn:

Holding the stop button energizes a booster pump on my carbureted onan 5.5kw, but the owners manual says to only prime if itís been run dry or the bowl drained.

TandW 04-23-2021 12:25 PM

We were talking about the O4000 Microlites.:facepalm:

craigav 04-23-2021 12:40 PM

Quote:

Originally Posted by TandW (Post 5724029)
We were talking about the O4000 Microlites.:facepalm:


I suspect a lot of the Onan's have a prime (maybe not the lpg models?). I purchased my RV used and in the plethora of manuals I didn't get one for the generator (onan 4000 microlite). In any case, I am certain on mine that holding the stop button down for more than a few seconds engages the fuel pump as I can hear it if the windows are open and it is quiet outside and a little light at the panel also lights up while holding the stop button in. Also, I am sure that the generator will start on the first or second try even when it has been sitting for a month, but only when I have held the stop switch down for ~30 seconds (once or twice), if I fail to prime it then it takes a very long time and many tries to get it started after sitting (there was a time early on that I didn't know about the prime function so I always prime if it has not ran in many weeks). Also, in the beginning I didn't know that all that was needed to turn it off was a simple ~1 second push of the stop switch as I used to hold it in until the generator completely stopped. Try it out, yours could be different but it is easy to test. ~Craig

cobia6620 04-23-2021 12:42 PM

I prime until the generator starts. I try to start every 15 seconds and if it doesn't start I prime another 15 seconds. I'm sure the old pump was weak and will have a final test of the new pump after 30 days when it's time for the next exercise.
just don't know what's normal.
I'll try and find specs for the Onan pump and run a flow test of the old pump to confirm it was weak. FYI I did install an Onan pump not an aftermarket unit.

TandW 04-23-2021 12:47 PM

Quote:

Originally Posted by cobia6620 (Post 5724047)
I prime until the generator starts. I try to start every 15 seconds and if it doesn't start I prime another 15 seconds. I'm sure the old pump was weak and will have a final test of the new pump after 30 days when it's time for the next exercise.
just don't know what's normal.
I'll try and find specs for the Onan pump and run a flow test of the old pump to confirm it was weak. FYI I did install an Onan pump not an aftermarket unit.

Once again, from the troubleshooting section, pressing the "Start button" energizes the fuel pump.:popcorn:

craigav 04-23-2021 01:23 PM

Quote:

Originally Posted by TandW (Post 5724049)
Once again, from the troubleshooting section, pressing the "Start button" energizes the fuel pump.:popcorn:

I don't think anyone disagrees that pressing the "Start" button energizes the fuel pump, if it didn't then the generator wouldn't run... :) The question is about the amount of time it takes to prime. I will add back to the OP, when mine hasn't ran for only a couple of weeks I usually only need to prime for 15 seconds then if it doesn't start, I prime another 15 seconds and then try again like you mentioned and that is usually enough. I only need a 30 second prime in the winter and for those times when I may not have ran the engine for 4~6 weeks (which I try not to go that long).. but sometimes I get delayed and I don't exercise the generator for 4~6 weeks and in those cases I start with a 30 second prime and if it doesn't start right away, I prime a second time for around 30 seconds which is about the longest prime time I have ever needed. ~Craig

TandW 04-23-2021 01:36 PM

All this prime time leads to worn out starter bearings. Do like the manual says, run it every thirty days at 1/2 load. It is what it is. If you think tapping on the can keeps the foam down, then go for it. In the meantime, I'll be ready for another.:dance::dance::dance::popcorn:

craigav 04-23-2021 01:44 PM

I am not sure we are on the same page, priming doesn't rotate anything, not the engine, or the generator, or the bearings, etc. priming just turns on an electric fuel pump (to correct myself, the fuel pump has a motor in it that rotates) and not too mention, the faster starting allows for the generator's electric starter to run a lot less which in turn will provide for a longer starter life. You really should try priming yours and see, if it starts faster for you after not running for an extended time period then I suspect you would like that it does and you don't have anything to lose if it doesn't.

F4Gary 04-23-2021 01:47 PM

Quote:

Originally Posted by craigav (Post 5724043)
I suspect a lot of the Onan's have a prime (maybe not the lpg models?). I purchased my RV used and in the plethora of manuals I didn't get one for the generator (onan 4000 microlite). In any case, I am certain on mine that holding the stop button down for more than a few seconds engages the fuel pump as I can hear it if the windows are open and it is quiet outside and a little light at the panel also lights up while holding the stop button in. Also, I am sure that the generator will start on the first or second try even when it has been sitting for a month, but only when I have held the stop switch down for ~30 seconds (once or twice), if I fail to prime it then it takes a very long time and many tries to get it started after sitting (there was a time early on that I didn't know about the prime function so I always prime if it has not ran in many weeks). Also, in the beginning I didn't know that all that was needed to turn it off was a simple ~1 second push of the stop switch as I used to hold it in until the generator completely stopped. Try it out, yours could be different but it is easy to test. ~Craig

In looking in the Q4000 Owners Manual pdf it appears it can only be primed with the switch that in on the genny and not the switch mounted inside the coach.

The Control Switch is labeled Start and Stop/Prime and has the little yellow light. The switch on the dash does not.

TandW 04-23-2021 01:54 PM

My O4000 Microlite is in another state right now. But I can assure you that the rubber covered start/stop switch on the generator does not illuminate anything at the generator.:popcorn:

craigav 04-23-2021 02:36 PM

1 Attachment(s)
Quote:

Originally Posted by F4Gary (Post 5724120)
In looking in the Q4000 Owners Manual pdf it appears it can only be primed with the switch that in on the genny and not the switch mounted inside the coach.

The Control Switch is labeled Start and Stop/Prime and has the little yellow light. The switch on the dash does not.

It is about to storm here, but as I was going to the mailbox I stopped by the RV and decided to start the generator for a few minutes. I am in agreement that it is certainly possible that my generator remote is different than some others (likely in fact), with that in mind I looked on Ebay for a replacement onan generator remote start switch and some of those show "Start Stop" only (like mine but different style) and some show "Start Stop\Prime". I tried to find a wiring diagram that indicated a difference between the two styles but they all seem to be wired the same so perhaps it is the controller on the generator that makes the difference. In any case, on mine, if you hold the stop button down for more than ~3 seconds it lights up and as today (I left the door open) I hear the fuel pump running after 3 seconds of pressing stop. I may not have even needed a prime today though as I had it running a week or two ago, in any case, I held the stop button down, 3 seconds later it lights up as in the picture, held for 15 seconds and pushed start and the generator started right up after maybe 5 seconds starter run time. So all in all, the remote start prime function certainly may be different in certain years and certain model remotes.

Also, as I was thinking, I think the need to prime is related to whether or not the carb fuel bowl is full, half, or empty, which got me to thinking why and where the fuel went. I searched on gasoline evaporation rate and found that there is not specific rate of evaporation as it all depends on the fuel blend, the altitude, the temperature, along with many other factors, so what I suspect is that evaporation occurs faster in the winter and regardless if that is true or not, the need to prime and for how long I believe is related to how much fuel is in the carburetor fuel bowl to start with, sometimes more sometimes less, all depends and the longer you go without starting, the more likely it would be to have less fuel in the carb which relates to more prime time. Not too mention of course, as the reason cobia6620 replaced his fuel pump, a weak pump certainly would take longer to prime than a new strong fuel pump. ~Craig

twinboat 04-23-2021 02:52 PM

Go to your generators and push the stop button. That first 5 seconds is STOP.

If you hold it for longer then 5 seconds, it goes into prime mode. Have someone listen to the generator and they will hear the fuel pump running, tick, tick, tick.

Once the carb bowl is full,the pump stops ticking, because its pumping against a shut needle valve.

You guys can go back and forth with the books, but that's how it works on my Generac 5500 AND our Onan Microlite 4000s.

Cranking the engine repeatedly for 15 second intervals is a starter killer.

F4Gary 04-23-2021 03:36 PM

OK, I'mma gonna bow out as I don't have a Q4000, I also have the 5500.
Here is the owner manual that I was referencing. Scroll down to page 1-4 and it describes it and the start/prime procedure it after that.


Cummins Onan RV QG4000 Generator Manual

craigav 04-23-2021 03:51 PM

Quote:

Originally Posted by twinboat (Post 5724180)
Go to your generators and push the stop button. That first 5 seconds is STOP.

If you hold it for longer then 5 seconds, it goes into prime mode. Have someone listen to the generator and they will hear the fuel pump running, tick, tick, tick.

Once the carb bowl is full,the pump stops ticking, because its pumping against a shut needle valve.

You guys can go back and forth with the books, but that's how it works on my Generac 5500 AND our Onan Microlite 4000s.

Cranking the engine repeatedly for 15 second intervals is a starter killer.


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.

craigav 04-23-2021 04:03 PM

Quote:

Originally Posted by F4Gary (Post 5724237)
OK, I'mma gonna bow out as I don't have a Q4000, I also have the 5500.
Here is the owner manual that I was referencing. Scroll down to page 1-4 and it describes it and the start/prime procedure it after that.


Cummins Onan RV QG4000 Generator Manual

It is all good, and I hope no one ever gets offended with this type of discussion as for sure offending anyone is not and would never be my intention and I know there was a time (years back shortly after I purchased mine) that I didn't know about the prime function until a fellow RV'r told me about it and suggested for me to try holding the stop button down for ~15 seconds and see and sure enough... I also didn't know I didn't have to hold down the stop button to shut off the generator, just a simple one second quick push. I will add that even though the manual you shared doesn't reference a prime function on the remote, that mine and as others like the person who told me about it many years back do have that ability, in fact you can purchase a replacement remote that has the word "prime" on it although it certainly could be the case that the generator has to support that ability. Thanks, Craig

cobia6620 04-24-2021 05:23 AM

1 Attachment(s)
thanks to all for all the good info
I do have Q4000 Model KY Spec L and have found generator parts plus operator and service manuals for this generator online.

I have thee start stations--- in the cab, near the rv door and on the generator. The hour meter is located by the rv door. All three switches will prime the pump if the switch is held in the stop position for a few seconds. Using the one in the cab with the door open allows me to hear the fuel pump run as the generator is below and behind the cab.


this is in the rv manual:

Generator Operations
To start the generator:
1. Press generator remote switch until generator
is running.
2. To stop the unit, press switch and release.
If the generator is slow to start, DO NOT hold
the switch in the START position for more than
10 seconds. Release the switch, wait 15 seconds,
then try to start again. This will help avoid
overheating and damage to the generator starting
system.

The generator operator manual is attached

I agree trying the starter every 15 seconds is bad and will switch to 30 seconds. With the new pump I should only have to prime once. If I don't prime it will not start after sitting 30 days. I never hold start button for 10 seconds-- 3-5 at most

I'm a retired engineer, grew up on a farm, and am no stranger to gasoline engines. When I was young we did not have computers and had to learn on our own which was rough and painful. Today the information available is unbelievable.

What is frustrating is not being able to obtain accurate manuals, elec diagrams and schematics for my rv. I've contacted Fleetwood numerous times and they have sent me all they have which are generic and often not accurate. So I've created my own and due to no rv certified tech being close I have to do all my own maintenance and troubleshooting.

The info I've obtained from the forum is priceless. I always believe that what ever problem I encounter someone else has had it before- so why not learn from others.

Mudfrog 04-24-2021 11:25 PM

Quote:

Originally Posted by F4Gary (Post 5724120)
In looking in the Q4000 Owners Manual pdf it appears it can only be primed with the switch that in on the genny and not the switch mounted inside the coach.

The Control Switch is labeled Start and Stop/Prime and has the little yellow light. The switch on the dash does not.

Maybe on some rigs. On ours, I prime the Microlite 4000 by pushing and holding the "stop" button inside the rig. The hour meter will display a symbol and I can hear the pump run.

If I think the genset needs priming, I hold the stop button in for a few seconds, release, then hit the start button to crank the genset.

twinboat 04-25-2021 01:22 AM

Gasoline evaporates from the carburator bowl in 2 to 3 weeks, so its basicly out of gas.
That's why you prime it.

THenne1713 04-26-2021 12:37 AM

My 22-yo Emerald Plus (BGE/4kw) has no codes/ no prime function, and 3-yo fuel pump, I typically crank 3-seconds, pause 3-seconds; repeat, will generally start by 3rd crank, (occasionaly 4th) even if not started in 2-3 weeks.

Mudfrog 04-26-2021 09:45 AM

Quote:

Originally Posted by THenne1713 (Post 5727336)
My 22-yo Emerald Plus (BGE/4kw) has no codes/ no prime function, and 3-yo fuel pump, I typically crank 3-seconds, pause 3-seconds; repeat, will generally start by 3rd crank, (occasionaly 4th) even if not started in 2-3 weeks.

Holding the start button in energizes both the pump and the starter motor. The carburetor will fill with fuel during cranking but it could take several seconds. I figure that being able to prime first, via the stop button, simply helps to save the starter motor from excess use (heat build up).

Unclepaul 04-29-2021 09:04 PM

This is perhaps the greatest discovery for me in years of forum reading. Each month, to exercise the unit, I used to need to crank the generator for at least 30 seconds to get it to fire up. Would push for 15 seconds, let it wait for 15 seconds, then toggle it again. Sometimes took 3 cycles to get it to start. Now with the priming learned, it usually starts up in just a couple seconds. I hated to crank it so much, but thought that was just the way it was. Sometimes I am starting the generator when boondocking, and often the batteries are kinda low, so long cranking was not optimal. So happy now...

Phil G. 04-30-2021 10:18 AM

This discussion has me scratching my head a bit: In our MH with the generator not running, pushing the generator rocker-type switch to it's STOP position causes the Onan generator's fuel pump to run - we can hear it's low muffled pulsating sound - so we know that the generator priming function is happening and just let up on the rocker switch to stop the priming after a few seconds.

To start the generator we just push the rocker switch the other way to it's RUN position momentarily one, two, or three brief times - as required - so as to fire up the generator.

It's all very simple ... I guess maybe because we can actually hear the Onan's fuel pump running for the priming function before we start it?

craigav 04-30-2021 10:32 AM

Yes, all very simple. I did read somewhere that not all generators have this "primer" function but for sure most do. I will add that the fuel pump will stop pumping anyway once the carburetor is full of fuel. So you may want to hold the primer down longer until you hear the pump stop "clicking" as there is no harm in doing so, and that will result in a faster start time than holding it only for a few seconds (assuming the carb wasn't still full of fuel after a few seconds of prime). Also as a quick note, this type of primer is not what some of us old timers consider a "prime", in other words holding the primer down for more time than needed will not flood the engine with fuel compared to a bulb type of primer (such as on small engines) that actually push (squirt) fuel into the engine's intake. ~Craig

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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