1992 Onan Microlite 4000 quagmire

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B737doc

B737doc

Well-known member
Joined
Jun 29, 2017
Posts
71
Location
West Georgia
  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. 
 
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.
 
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!!!
 
Lol. There you go. Oil, fresh fuel, regular operation. My grandfather used to say if you don't use it you lose it. ?
 
  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!
 
Backfire could be fuel mixture in exhaust then high temp ignites it. Is there an anti diesel solenoid on the carb bowl?
 
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?
 
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....
 
Does it have about a one inch diameter device screwed into the carb bowl with a wire coming off of it?
 
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
 
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