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Author Topic: 1992 Onan Microlite 4000 quagmire  (Read 381 times)

B737doc

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  • Posts: 62
  • 1992 Challenger
1992 Onan Microlite 4000 quagmire
« on: October 10, 2017, 02:38:02 PM »
   When I bought my MH a couple of months ago, the Genset would only start by manipulating the choke.  Finally received the shop manual after thoroughly screwing it up royally!  I kept screwing screws to the point it wouldn't even run at all, and locked up the starter in the process.  Removed the Genset and found starter gear bound to flywheel locking up the engine.  Ordered new starter for $35 awaiting delivery.  The manual says to "adjust engine speed to obtain a certain RPM.  I have no way of determining RPM, and hope that adjusting the speed while monitoring output voltage will get me close. I have a really nice fluke, but not sure if it measures Hz or not. Anyone been here before?   Ive got the choke set per the shop manual, and will just go from there I guess.   
1976 BMW R90/6 "Airhead"
2005 Triumph Bonneville "America"
1992 Challenger Motorcoach

QZ

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  • Posts: 307
Re: 1992 Onan Microlite 4000 quagmire
« Reply #1 on: October 10, 2017, 07:15:52 PM »
60 hz is 3600 RPM.  Use the hz function and adjust the engine speed until you see 60. There is a procedure for adjusting the governor but if you haven't messed with that dont do anything. I'm talking about the shaft that goes into the crankcase and the main governor arm fits over it and locks on with a pinch bolt.  There should be an adjustment screw or rod that pulls on the spring. If the base arm adjustments have not been messed with you should be able to adjust the engine rpm with that screw or rod to get 3600. You might set it just over that as it will drop a little when loaded. You cant get it perfect for all loads but you can get it close.

The gov arm/flyweight adjustment usually doesn't need to be messed with because surging, bogging etc are often carb/fuel system related. Be very careful before you do mess with the flyweight system as turning the arm the wrong way can cause internal damage and you will be splitting the cases!!!!! I dont know if Onan is that way but I have seen it.
« Last Edit: October 10, 2017, 08:26:49 PM by QZ »

B737doc

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  • Posts: 62
  • 1992 Challenger
Re: 1992 Onan Microlite 4000 quagmire
« Reply #2 on: October 20, 2017, 07:24:15 PM »
New starter arrived and installed. Could see on the threads of all adjustment screws exactly where everything was before I dicked with it. Adjusted choke and mixture screws per manual, reinstalled unit, unit started like new.  Stuck Fluke probes into outside power outlet and read 123-124 VAC.  Loaded set, now reading 122-123 VAC. Not touching the darn thing ANYMORE!!!
1976 BMW R90/6 "Airhead"
2005 Triumph Bonneville "America"
1992 Challenger Motorcoach

QZ

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  • Posts: 307
Re: 1992 Onan Microlite 4000 quagmire
« Reply #3 on: October 20, 2017, 09:34:46 PM »
Lol. There you go. Oil, fresh fuel, regular operation. My grandfather used to say if you don't use it you lose it. 😀

B737doc

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  • Posts: 62
  • 1992 Challenger
Re: 1992 Onan Microlite 4000 quagmire
« Reply #4 on: November 02, 2017, 04:00:06 PM »
   Still running good for the most part.  Still suddenly stalls momentarily, but recovers.  On shut-down, the last stroke backfires louder than a .22 rifle!  Cracks me up every time!
1976 BMW R90/6 "Airhead"
2005 Triumph Bonneville "America"
1992 Challenger Motorcoach

QZ

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  • Posts: 307
Re: 1992 Onan Microlite 4000 quagmire
« Reply #5 on: November 02, 2017, 08:14:11 PM »
 Backfire could be fuel mixture in exhaust then high temp ignites it. Is there an anti diesel solenoid on the carb bowl?

Charlie 5320

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  • Posts: 1998
Re: 1992 Onan Microlite 4000 quagmire
« Reply #6 on: November 03, 2017, 09:56:15 AM »
It's NOT supposed to backfire, and if you let it continue you WILL end up blowing a head gasket. Backfires are also very hard on mufflers. Are you letting it run a few minutes unloaded before shutting it down?
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

B737doc

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  • Posts: 62
  • 1992 Challenger
Re: 1992 Onan Microlite 4000 quagmire
« Reply #7 on: November 03, 2017, 02:24:38 PM »
Yes....I make sure it's unloaded, and stabilized before shutting it off.  I've tried leaning and richening the mixture, all to no avail. It doesn't do it EVERYTIME, just most of the time....
1976 BMW R90/6 "Airhead"
2005 Triumph Bonneville "America"
1992 Challenger Motorcoach

QZ

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  • Posts: 307
Re: 1992 Onan Microlite 4000 quagmire
« Reply #8 on: November 03, 2017, 03:22:39 PM »
Does it have about a one inch diameter device screwed into the carb bowl with a wire coming off of it?

WILDEBILL308

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  • Posts: 2417
Re: 1992 Onan Microlite 4000 quagmire
« Reply #9 on: November 03, 2017, 08:58:10 PM »
One thing I would recommend you do is to run a rich mixture of a good carb cleaner through it like sea foam. My favorite way is to use a 5 gal can with about 3-5 gallons of premium gas and a can of sea foam. run a rubber fuel line into the gas can so you don't need to treat your full tank. You should run it under about 3/4 load for 2 hours every month. You might try loading it when running the sea foam.
Let us know if this helps.
Bill
2003 Bounder 38N
300 HP 5.9 Cummins
Allison 3000MH Trans.
Towing 2014 Honda CRV
Home base Fort Worth, Texas
A man who carries a cat by the tail learns something he can learn in no other way.
-Mark Twain-

 

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