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Tool Talk Discussion Forum

Onan generator mocroquite 4000

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Matt S Illinios

10-31-2012 05:19:20

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Kind of a tool question. I have an Onan 4000 microquite generator on my RV. I haven't ran it in a couple of months so was going to winterize it and it won't start/stay running. I can get it to start for a second then it dies. I pulled the gas line off the carb and there is gas pumped there but not sure if enough. Do you have any other sugestions for me to try before I take it to an Onan dealer?
Thanks in advance.

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36 coupe

11-12-2012 02:43:58

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
My chain saw began to start hard and run lousy. Acted like a gas problem , changing the spark plug fixed the problem.Always try the easy thing first.

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Brian G. NY

11-03-2012 09:08:00

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
I just had an experience with a Craftsman (rebadged Generac) 4200 watt generator at my M.I.L.'s in Connecticut during their recent power outage.
It would start, run for a few seconds and quit.
Turned out that when I bypassed the "low-oil cutoff" it would run perfectly.
It was not low on oil and apparently there is nothing wrong with the engine as we ran it for 8 hrs without any problems or unusual noises. We then changed the oil and filter using full synthetic 10W30 oil. It still would not run without bypassing the "low-oil cutoff switch".
Conclusion: bad "low-oil cutoff" switch.

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Billy Shafer

10-31-2012 15:54:24

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
First don't take it to an Onan dealer unless you just have to. Most things you can fix yourself.
1 See if it is producing AC voltage when it is running. If it is then you need to check out the carb. The carbs on this unit would varnish up very fast if not run often.
2 The shut off valve under the carb is working if it runs at all. It runs off of the ignition system.
3 About how long does it run.
4 Most people have had good luck with cleaning them. Just be careful with gaskets. As there are no kits available that I know of.
5 If you do need a new carb. Try ebay or smokstak Onan section

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Matt S Illinios

11-01-2012 04:49:43

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 Re: Onan generator mocroquite 4000 in reply to Billy Shafer, 10-31-2012 15:54:24  
When it starts it only runs for a very short time. Like maybe seconds. So I am thinking dirty or the electronic fuel shutoff on carb. will try and look at it tonight, hopefully if wife doesn't have other plans for me.

Thanks for all your help guys.

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10-31-2012 07:06:58

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
the newer ones ive dealt with flash out a fault code on the lighted start sw. You could be losing exciter voltage also. Start overrides the circuit that operates the fuel cutoff in carb ,once engine starts exciter voltage holds it open. Common problem,and not too hard to fix yourself if you have some help getting unit up on bench. Most of the time you can simply replace brushes and clean the slip ring good. Go to onans website and you might find a copy of the fault codes and how to read them,if yours even has that option. i think they also still have manuals online .Engine acts as if its running out of fuel when this happens,and it actually is ,but its a electrical problem ,not fuel problem.

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Matt S Illinios

10-31-2012 07:25:02

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 Re: Onan generator mocroquite 4000 in reply to jackinok, 10-31-2012 07:06:58  
Can't put it on a bench. Generator mounted on top of RV trailer. The code is "36" in which is out of gas, change air filter, clean/change plug. Can you give more details about the "fuel Cutoff" in carb? I am going to try and clean it as well tonight. Thanks Matt

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10-31-2012 08:53:38

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 07:25:02  
nearly all the modern gensets have a plunger type affair in bottom or side of carb thats electricaly controlled. usualy a single wire to it.its purpose is to cut off fuel flow in case of accident,emergencies,fire etc.basicaly to stop engine from pumping fuel into a fire or something of that nature.they normally dont shut off fuel to the engine persay,but block the main jet passages in carb. this gives a much faster shutdown since carb doesnt have to run out of fuel in your onan carb ,if i recall on your model correctly its in the bottm of carb, has a single white wire to it.THAT for all intent and purposes is the main jet in your carb and if its closed,engine runs out of fuel in just a second.if your carb is blocked up very often ,( more often than not) unscrewing this will allow you to pullit out,and carb bowl will drop off.once its in your hand main jet passages will be in the tube attached to the end of solenoid ,and thats basically all the jets/orifices in the carb.clean bowl of course,and clean the orifices on solenoid good. before reinstalling spray some carb cleaner up into body of carb where tube goes in,because its common for bits of orings to get lodged there.make sure orings are good on solenoid and reinstall. to check power,use a voltmeter and check voltage at white wire and body of genset,should have voltage with switch held in start position(engine cranking).if voltage goes away as soon as engine starts,you most likely have either a exiter voltage problem,or a control board. if voltage stays and engine dies, either you have a problem with the plunger type solenoid itself,or a fuel delivery problem. (note) they WONT seem to pump much fuel when engine is cranking,simply because they are cranking at maybe 100-200 rpms,once engine starts its running several times that and it will pump far more. if you question fuel delivery system up to the carb simply gravity feed your fuel directly into carb from a safe source and bypass it all. if engine runs you know you have a fuel or fuel delivery problem. first thing i would do is try some fresh fuel if it were mine. if i recall right exciter voltage fault code is 33 (going by a old mans memory here so dont trust that too far),so that means at least the control board says you have it.once its past that point fault codes wont show a problem so also check for a broken or loose/corroded connection between there and carb. any fault basicaly thats not found electrically most likely defaults to 36 or a fuel problem. if engine wont run with no electrical faults thats the next most logical step,but fault codes wont show up if the electrical problem is past the point where voltage is tested if that makes any sense. hope this helps. I dont think ive ever seen a genset on the roof,must be a new thing they are doing.lokks to me as if that would amplify the noise a genset makes sort of like being inside a drum.

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John T

10-31-2012 06:11:27

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
Ive had Onans in RV's for yearsssssssss. I currently have a "Microquiet" 4000 KY Spec J which I just had to install a new "control board" at great expense to get it running grrrrrrrrrrr. I DONT LIKE THE MICRO"QUIET" what a misleading name grrrrrrr they are single cylinder so they have to scream n run wild at like 3600 NOISYYYYYYYYYYYYY RPM. Give me the old 2 cylinder 1800 RPM Emeralds anytime. HP is a function of Torque X RPM so with that single cylinder they have to get HP by running at more RPM grrrrrrrrrrrrr

PS many RV products utilize control boards which are built on like a printed circuit card and rebuilders like Dinosaur Electronics can furnish new or repaired ones wayyyyyyyyyyy less then what the manufacturers sell them for AND ALL I BOUGHT HAVE WORKED PERFECT AND LASTED. HOWEVER on the Onan Microquiet they are built in a heavy frame and its all potted (epoxy or whatever) and the rebuilders dont repair them and guess what !! You have to get them from Onan grrrrrrrrr $350 on Flea Bay and like $450 from an Onan dealer grrrrrrrrrrrr

Anywho, over many years Ive had ones that starve for gas but I was always able to remove the carb and clean them sufficiently to completely cure the problem yayyyyyyyyyyyy. I now always install a small inline fuel filter after the pump and before the carb.

MAINTENANCE NOTE:::::::: Its best to "exercise" them often cuz sitting for long periods isnt good on the carbs. At least once a month or even more often I start mine n let it run under a load and I have Sta Bil in the gas AND DOING ALL THAT SURE HELPS !!!!!!!!!!!!!!

To troubleshoot I have installed a temp fuel line direct from the pump stuck down in a can of gas to see if that cures the problem??????? If so I look for restrictions in the long line from the RV tank to the Onan. Ive also ran a gravity line direct to the carb to see if that cures the problem like a defective pump etc. As Im sure youre aware, the fuel line to the genny doesnt extend as deep into the RV tank so if youre much below 1/4 tank the genny doesnt get gas.

We dry camp a lot in Utah and Colorado and Arizona and Florida so the genny sure comes in handy and we use ours a lot, but if I had my druthers Id have the older 2 cylinder 1800 RPM unit verus the NOISY so called Micro"Quiet" YEAH RIGHT

Id love to hear an honest opinion of what the Onan service tech who posted thinks about the Microquiet? Am in the ONLY one who dont like them lol

Best wishes

John T

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Dusty MI

10-31-2012 17:04:40

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 Re: Onan generator mocroquite 4000 in reply to John T, 10-31-2012 06:11:27  
We don't use ours a lot, so what I have done is added a switch to the wire that feeds the fuel pump, and after using it I turn the fuel pump off and let the generator run out of gas emptying the carb, there fore no fuel in carb to gum up.

We've had it for 10 years and so far so good.


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Billy Shafer

10-31-2012 16:17:19

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 Re: Onan generator mocroquite 4000 in reply to John T, 10-31-2012 06:11:27  
Well John since you asked.
1 They are good for what they are. They will do their job. But they have faults.
2 Noisy and have a short life at 3600RPM. Unless you take very good care of them.
3 Control board is sealed so no repairs can be done.
4 Hard to work on. If you need to do any major repairs. The top has to come off.Which means in most cases you have to pull the unit out.
5 I prefer the older 1800 RPM units.
6 Would I buy one. No. I would look for an 1800 unit and make room for it.

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John T

11-01-2012 04:27:31

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 Re: Onan generator mocroquite 4000 in reply to Billy Shafer, 10-31-2012 16:17:19  
THANKS for your input, I'm seriously looking for an Emerald Plus 1800 RPM provided I can find one that fits in the compoartment where my Micro"quiet" (Yeah right) is located.

John T

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Billy Shafer

10-31-2012 05:40:22

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 Re: Onan generator mocroquite 4000 in reply to Matt S Illinios, 10-31-2012 05:19:20  
Get a gas can with some cleaner in it. Hook it up to the pump. See if you can get it to run by holding the choke closed a little. Or if it will run let it run on the cleaner mixture.

Your carb is clogged up. The Onan dealer is going want you to buy a new carb. At over two hundred dollars. If you are good with engines. You can remove the carb and clean it. Just be careful with the gaskets.

Onan tech since 1980

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