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 > How perfectly should my Onan run?

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Straylight

The Road

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Joined: 07/11/2018

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Posted: 07/11/18 06:47pm Link  |  Quote  |  Print  |  Notify Moderator

Hi all! I've lurked here for AGES to fix all my tech issues; you're all very helpful. I'm looking for some info about my Onan Microlite 4KY Spec H generator.

The gist of my question is this: When it's running correctly, should I NEVER hear a surge and should my hz + volts be nearly perfectly stable?

The generator surged endlessly and did not run when I bought the RV. I have never heard an Onan generator running, so I have no idea if my interventions have made it "good as it'll get" or if I should still tinker with it.

Here's the history:

  • Clogged carburetor from lack of prior owner use: Took it apart, cleaned it, took it to a small engine shop for an ultrasonic bath.
  • Current gas tank: Regular gas, a can of Seafoam, and most of a can of Berrymans B12.
  • Replaced carburetor gaskets, plastic float doohickey, float pin, float hinge. (Onan carb repair kit)
  • Melted circuit board: Diagnosed at Onan shop; I put a new OEM part in.
  • Bad fuel pump wiring/Prior owner had bypassed fuel pump/Fuel pump was trash: Long story short, I replaced the fuel pump with an aftermarket Airtex pump and wired + connected it correctly.
  • Replaced fuel filter with very nice new inline filter before the pump.
  • Replaced spark plug with new Champion plug. Correctly gapped.
  • Changed oil.
  • General wipe-down, inspection, WD-40 on the governor and choke moving parts.
  • Most recently: Dialed in speed screw, governor sensitivity screw, and idle stop screw according to (edit: I can't put in links, but I used user hndymn's guide posted on this forum on a topic called "Onan generator frequency adjustment?" to adjust these settings).


My resources:
  • Local Onan shop is full of super friendly guys who seem to like me. I've ordered some parts from them. I'm already $600+ into the shop for the control board diagnostic and the control board itself; I'd rather not spend too much more cash. Plus, I like learning about my genny!
  • Onan Master Service Manual, plus the service manual for my genset.
  • All the correct tools and easy access to the generator.
  • A Kill-A-Watt that I plug into an extension cord that is plugged into an interior outlet on my rig.
  • An air conditioner that pulls about 2000W and a microwave that pulls about 1000W. (My "load bank"!)


Here's where we stand now:
I'm getting consistent hertz readings between 61-63 at idle and 58-61 under 2000W load (call it half load, from the air conditioner). My voltage is generally between 110 and 130, up towards 127 at idle and down towards 118 under 2000W load. My voltage is never perfectly steady: When it's running at its best, it goes up and down a volt or two. The generator will run forever if I let it; it does not die. It no longer coughs or sputters. When I hold the throttle tang against the stop screw, I drop down to 54-56 hertz and it will stabilize at that speed (usually 54.7 or so) and will not die.

However, every minute or so under 2000W load it will slow down and then surge once; once in a while, it will hunt up and down for a few seconds. When idling (that is, with a nominal load, when the rig is plugged in but everything I can turn off is off), it will surge slowly but rhythmically.

I have been able to adjust it so it runs perfectly at idle, but when I do so, it's running at 66 hz. I can also adjust it so it runs a little better than previously described under 2000W load, but when I do THAT, it runs worse at idle.

When I load it suddenly to 2000W, it will hunt up and down about five times before it settles on the correct speed.

Is this pretty much as good as I should expect it to get? Should I keep tinkering with the speed and governor sensitivity? Is there something I've missed?

Some final thoughts:
  • The only things I haven't done are replace the air filter and put a brand-new carburetor in it.
  • My Spec H carb has a tamper-proof idle mixture screw. There is a vertically-mounted, very small screw directly below the throttle stop screw; I have not adjusted this screw, other than to remove it and clean it. There is an altitude adjustment, which I have at its lowest setting (I'm in Virginia), and directly below the altitude adjustment is a large screw that I think is the main carb adjust; I have removed that and cleaned it, and it is currently about as far in as it will go without putting a whole bunch of force on it.


I'd love to hear your expertise!

Lwiddis

Los Angeles :(

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Posted: 07/11/18 06:57pm Link  |  Quote  |  Print  |  Notify Moderator

Seems you left out the details. lol


2015 Winnebago 2101DS TT & Tahoe LTZ, 300 watts WindyNation solar-parallel & MPPT, Trojan T-125s. TALL flagpole for US flag. Prefer USFS, COE, BLM, NPS, TVA, USF&WS, state & county camps. Bicyclist! 14 year Army vet - 11B40 then 11A - old MOS 1542 & 1560.


garyemunson

Reno, Nevada

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Posted: 07/11/18 07:13pm Link  |  Quote  |  Print  |  Notify Moderator

**** hard to ever totally clean those carbs. They are pretty much considered disposable. The generator should not surge except for a few moments at startup. I think there is still a carb problem on yours.

Son of Norway

Denver, Colorado

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Posted: 07/11/18 07:44pm Link  |  Quote  |  Print  |  Notify Moderator

Try a new governor spring. Then while it is running perfectly at idle, adjust the speed setting. Aside from the surging, your numbers are all within spec. You sure that your load is constant?


Miles and Darcey
1989 Holiday Rambler Crown Imperial
Denver, CO


maillemaker

office

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Posted: 07/11/18 08:11pm Link  |  Quote  |  Print  |  Notify Moderator

The place for serious tech support for Onan generators is here:

https://www.smokstak.com/forum/forumdisplay.php?f=1

Steve


1990 Winnebago Warrior. "She may not look like much but she's got it where it counts!"



DennisVR

NorCal

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Posted: 07/11/18 08:12pm Link  |  Quote  |  Print  |  Notify Moderator

Tried everything to clean my carb. Took it totally apart, carb cleaner, compressed air and nothing worked. Found a new carb on EBAY for $200 and replaced it and it runs great. Mine was the Onan 5500.

azrving

Oatman

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Posted: 07/11/18 08:42pm Link  |  Quote  |  Print  |  Notify Moderator

It sounds like you have the fuel delivery in order so it's probably not lean. I'd be sure the governor is set correctly. The gov is a balancing act between the flyweights and the gov spring. Any slop in the linkage or incorrect adjustment can cause that problem. Some linkages will have a very fine spring covering them. The spring connects to the arms that the linkage is in to take up the slop.

But being borderline lean could be an issue. What does the plug look like? Black, brown, white?

Old_Man

Somewhere, CA

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Posted: 07/11/18 11:14pm Link  |  Quote  |  Print  |  Notify Moderator

All this is all the more reason I'll ditch the Onan and replace it with a Honda. Onans are stinky and noisy.

MEXICOWANDERER

las peƱas, michoacan, mexico

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Posted: 07/12/18 01:35am Link  |  Quote  |  Print  |  Notify Moderator

I've seen too many micro Onans to believe in the tooth fairy. If the slight surge does not worsen and electrical output values do not escape the acceptable window I wouldn't worry about it. Woodward electronic governors are extremely expensive and the only small Onan I have seen run flawlessly was a 22 horsepower 4 cyl powering a 12,000 watt generator and it was on LPG. It had it's own problems with engine overheating > 9,500 watts. The old saturated field 6.5 NH was notoriously fickle but it was near bulletproof.
Trying a brand new carburetor is going to be pricey. I hope it works for you.

K Charles

Connecticut

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Posted: 07/12/18 05:57am Link  |  Quote  |  Print  |  Notify Moderator

The OP says he has not removed or adjusted the idle screw and the "main carb adjust" is screwed in as far as it will go. How did the OP clean the idle screw if he never took it out. I would first adjust the idle and main jet.





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