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Old 05-31-2018, 04:12 AM   #1
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Weird question concerning ONAN 4000 generator

We have had our VEGAS for two years and never had an issue starting the generator. I just always tried to start it a couple of times and then, on the third time, it would fire right up.

Never realized that the generator had a PRIMER on it. So yesterday, the generator refused to start. Found the PRIME function on the switch on the generator (and I am aware that the switch on the dash of the VEGAS also can be used to PRIME)

Anyway, primed the generator and still no fire. Then read in the manual (directions are always the last resort) last night that the PRIME needs to be engaged for 30 seconds... So, followed directions this morning, held the PRIME switch for a full 30 seconds, and the generator fired on the second start attempt.

So, sorry for the long post, how long do the rest of you PRIME the GENSET? 30 seconds seems like a long time (even though it did work), but since I really never primed it before just though I would ask.
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Old 05-31-2018, 04:18 AM   #2
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Never knew this...

Ours takes a few tries as well, from the toggle switch right in the door. I'm thinking a look up in the manual is in order. Good luck and thanks for the insight.
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Old 05-31-2018, 04:21 AM   #3
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Quote:
Originally Posted by Mo_Mike View Post
We have had our VEGAS for two years and never had an issue starting the generator. I just always tried to start it a couple of times and then, on the third time, it would fire right up.

Never realized that the generator had a PRIMER on it. So yesterday, the generator refused to start. Found the PRIME function on the switch on the generator (and I am aware that the switch on the dash of the VEGAS also can be used to PRIME)

Anyway, primed the generator and still no fire. Then read in the manual (directions are always the last resort) last night that the PRIME needs to be engaged for 30 seconds... So, followed directions this morning, held the PRIME switch for a full 30 seconds, and the generator fired on the second start attempt.

So, sorry for the long post, how long do the rest of you PRIME the GENSET? 30 seconds seems like a long time (even though it did work), but since I really never primed it before just though I would ask.
Yes, at least 20-30 seconds when I run it for its exercise each month. Starts on the 2nd or 3rd try.
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Old 05-31-2018, 10:39 AM   #4
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In the winter I usually have to prime it for the requisite 20-30 seconds (when its really quiet I can hear the fuel pump). Usually takes a long crank to fire up.
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Old 05-31-2018, 11:53 AM   #5
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You actually may need to prime up to 45 seconds. I talked about this in this thread:

Automatic Generator Prime Function
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Old 05-31-2018, 11:58 AM   #6
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Mine is the QD6000 diesel...I don't have a prime button. I press the start button and hold for 8 seconds and it starts. Same when I use the outside generator mounted start button. I guess the prime must be automatic?
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Old 05-31-2018, 12:08 PM   #7
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Mine is the QD6000 diesel...I don't have a prime button. I press the start button and hold for 8 seconds and it starts. Same when I use the outside generator mounted start button. I guess the prime must be automatic?
They don't have a prime button: You hold down stop for 20-30 seconds (the light will light up indicating that the fuel pump is running). I bet its the same for yours you just didn't know the procedure--maybe: The gas gennys have a carb which is why there is a prime procedure. If the diesel genny is fuel injected it probably doesn't have a prime.
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Old 05-31-2018, 12:21 PM   #8
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No light...no 20-30 seconds...no. Hold button for 7-8 seconds or so...and she starts up...release button. Simple procedure. Same as outside...no light...etc.
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Old 05-31-2018, 12:46 PM   #9
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Quote:
Originally Posted by JamieGeek View Post
They don't have a prime button: You hold down stop for 20-30 seconds (the light will light up indicating that the fuel pump is running). I bet its the same for yours you just didn't know the procedure--maybe: The gas gennys have a carb which is why there is a prime procedure. If the diesel genny is fuel injected it probably doesn't have a prime.
All diesels inject fuel directly into cylinder combustion area in one way or another. A small generator engine may use glow plugs to preheat for a few seconds. That may account for 8 second delay. Not sure.
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Old 05-31-2018, 12:54 PM   #10
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both gas and diesels need to be primed, but sometimes the time is little since the generator was run more recently, or the outside temps are warm.

my diesel Onan QDRV6000, which pulls diesel from my coach's fuel tank, can take 30 seconds to prime/start, or it may start right up, depending on the circumstances.

if you compare it to the 'old pull start lawn mowers, you can see that if you haven't started the mower in a while, you may take a few long pulls to get the fuel into the carb, and the engine 'warm' enough to get the spark to make 'fire'. If it's been cranked recently, it may only take one easy pull.
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Old 05-31-2018, 01:05 PM   #11
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Chance...correct! Just as in the GMC HD...wait to start. Fuel pump builds pressure, pre-ignition heaters go on...bang, start up. There are no "prime" lights. That light must be specific to the gas generators.
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Old 05-31-2018, 01:29 PM   #12
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My mower is very simple without a fuel pump, so a little different. Fuel flows by gravity into carburetor.

As I understand it, what makes generator engines a little different than newer cars is the location of the fuel pump. On newer cars and trucks the fuel pump is inside the fuel tank, so it pushes the fuel to the engine. Thatís very effective until you have to replace the fuel pump. Just had to do it.

My generator had fuel pump at the generator, so it had to suck the fuel from the vehicleís fuel tank. This is the way old cars like my Mustang are set up. Old cars normally had a mechanical fuel pump at engine, and if you didnít run them for a while, sometimes required cranking to fill the entire fuel system. With electric fuel pumps that operate independent of engine cranking, it can save battery capacity by just running fuel pump.

I suppose that proximity of generator to vehicle fuel tank and also relative elevations ďmayĒ affect priming some, but Iím not sure of that either. If so, not all generators will prime as quickly. Havenít looked into this much because my Onan, when I had one, usually started quickly.
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Old 05-31-2018, 01:51 PM   #13
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I never prime mine for the full 30 seconds...
I'll give the starter about a 10 second grind, and then re-prime.
It starts on the second or third attempt.
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Old 05-31-2018, 02:51 PM   #14
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I learned about the prime function on this forum. It has sped up initial start drastically. Also seems to eliminate the run for 5 minutes then stop it used to do.
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Old 05-31-2018, 09:12 PM   #15
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Never had the start problem. Followed procedure good to go. My problem is recently that the genny shuts down after 1 1/2 - 2 hours on its own. Anyone else experience that? Any ideas would be greatly appreciated, thanks
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Old 06-01-2018, 03:05 AM   #16
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Thanks for all the replies...

I guess that the directions DO work <grin>

I don't know why I always think I know better than the people who build things.
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Old 06-01-2018, 03:12 AM   #17
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RV QG 4000 Onan

Anyone have a source for the drain plug crush ring (metal gasket)?
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Old 06-01-2018, 11:36 AM   #18
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Old 06-03-2018, 05:41 PM   #19
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I hold prime/off button for a couple seconds after the light comes on. Maybe 7-8 seconds total than start it up. Always starts first time.

And i run my gen every 3 or 4 weeks with a/c on for an hour plus to get rid of condensation and get fresh gas to the cards.

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Old 06-18-2018, 12:37 AM   #20
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drain the carb, too!

I agree. Hold the STOP switch down until the fuel pump fills the bowl and press START . This usually takes less than 10 seconds. This is unnecessary if the genset has been run very recently.

At the end the trip, drain the carb bowl to prevent varnish buildup. Just connect a short length of fuel hose to the fitting on the bottom of the bowl and turn the drain screw until the fuel empties into a small jar. Dump the contents back into the fuel tank. (This last step may prevent a carb problems later.)
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