How perfectly should my Onan run?

[Straylight]

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!

[Dave_H_M]

Sigh, I putter around with small engines.

It seems the final remedy for the engine pfarting around (surging) seems to be a new carb. :R

[MEXICOWANDERER]

These are worth their weight in platinum...

https://www.ebay.com/itm/DIESEL-FUEL-FILTER-WATER-SEPARATOR-FOR-R12T-MARINE-SPIN-ON-HOUSING-120AT/16...




Carburetors clog because of moisture and exceedingly fine grit passing through the fuel filter. Check what Onan uses for microns filtration. The S series of RAcor filter is for ONE micron. I have cut open my generators RAcor element and found smoke like powder embedded in the media. It is impossible for moisture to penetrate never mind pass through one micron media.

With a pleated paper air filter no water vapor can enter your carburetor. I have one of the RAcor filters in-line with a 3/8" hose for Jesus to fill his 60 HP outboard. But the permanent installation will incorporate a Detroit diesel spin on pre-filter one quart cartridge capacity because the RAcor filter gets clogged too easily.

[pnichols]

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

So what remote start inverter technology 4KW Honda model are you going to mount neatly right into the exterior cabinet area where the Onan used to hang? 😉

[jplante4]

I didn't see if you cleaned the brush slip rings.

An old post from Generator Jim with lots of good info

post

[jplante4]

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

Not helpful.

[Old_Man]

Best thing you can do with an Onan is take it to Burning Man and burn it. Honda 1000 is all we'll need. Onans are obnoxiously loud and they stink the entire area.

Since I do not spend time in the cold I don't worry about Onans. I should probably sell it to someone...just taking up space back at the Howls, maybe I'll sell it cheap to some people who need it, or just give it to them. Ask them to pay it forward if they get a chance.

[pryoclastic]

Generator Jim wrote:
One thing for the future troubleshooting. The paper air filter can become oil soaked because the crankcase breather tube dumps into its intake airstream. If so, it will act like the choke is on and cause over fueling problems.

Thanks for posting! This is actually a really good tip. I noticed this was the case on our air filter when I first started going through the generator systems after we got our coach.

Over fueling could also explain why the plugs smelled like gas.

Confirm / deny?

(btw .. username checks out)

[Generator_Jim]

One thing for the future troubleshooting. The paper air filter can become oil soaked because the crankcase breather tube dumps into its intake airstream. If so, it will act like the choke is on and cause over fueling problems.

[Straylight]

I got my carb straight from my Onan dudes. It was $270ish after the 10% Power Club discount, and they had it in stock on the shelf.

[gmctoyman]

Your source for the carb ?

[Straylight]

After taking all the other interventions I could, I swapped out the carburetor with a new one.

The singing of angels, gentlemen: A high and far-off song of joy, ten thousand thousand voices joined in ecstasy. It spins like a top, ticks like a sewing machine, purrs like a cat.

I honestly sort of eyeballed the speed and sensitivity after I put in the new carb, but even with "eh, I'll adjust it more precisely after I turn it on" the thing still ran perfectly. Eventually dialed up the speed just a smidge and tweaked the sensitivity for kicks; smooth response to adjustments, no surging at all, will take any load. My hz fluctuations went from +/-2hz when running "perfectly" to +/-0.5hz. My voltage stays within a single-volt range.

Wish I had replaced the carb earlier, but I didn't waste much money that wouldn't have gone toward thoughtful preventative maintenance anyway (spark plug, oil, new springs, some high-energy petroleum distillates, fuel pump, fuel filter: all of these things either strictly needed replacing or were worth getting anyway before I drove off to Nowheresville USA). Mostly just time and frustration, which I've got plenty of.

Notes, in no particular order:

• To replace the main governor spring, I backed the speed adjustment screw all the way out (counter clockwise) and put the sensitivity adjustment screw all the way in (clockwise). This collapsed the spring very close to its completely relaxed position and allowed me to install the new spring without stretching it very much. I then dialed both screws back to something like their original position before I started the genny again.
• On earlier repairs (fuel pump, control board) I went out of my way to clean the genset and replace bad wire terminals. This was helpful AND taught me more about what parts lived where. I also learned not to trust PO's wiring (the bad aftermarket fuel pump was not only bad, but was miswired; my Onan guys caught this right away, after which I snagged a wiring diagram and puzzled out the correct configuration).
• If there was a way to clean that KY Spec H carburetor, I tried it. I started out light, with Seafoam (many guys swear up and down that Seafoam is only for fuel stabilization and will not clear out gunk; I can't disagree), then with Berrymans B12, then with Birkebile 2+2 on a disassembled carb, then more Berrymans and Seafoam put through the running carb, then to a small engine shop's ultrasonic bath. The performance improved, but it never got close to what I'm seeing with the brand new carb. It's possible that these interventions will work if your carb is gunked from a season of fuel varnish, but I was staring down years of POs not using the generator at all.
• The control board was not fried when I bought it; I think I fried it when I was starting it over and over (with bad wiring!) to feed gas through the carb. If I had another chance, I'd replace the carb immediately; I think the control board would still have fried from the wiring issue, but maybe not. My symptoms for the fried control board were that the generator wouldn't even engage the starting solenoid, not even a click. The Onan guys diagnosed it, and when I saw what the board looked like, it was very obviously melted.
• The original starter solenoid, God bless 'er, is still perfect.
• I'll be stabilizing all the fuel that goes through the rig's main tank (which feeds the genny). Cheap insurance.
• It runs more quietly with the new carb, in addition to more smoothly. Adjustments to the speed and sensitivity also no longer cause wild reactions in engine speed and surging. This could be from the new springs, but I'm pretty sure it's the fact that the carb is healthy now.
• Armed with the service manual, a wiring diagram, the right tools, and a clean workspace, I didn't find any of the work I performed to be terribly difficult. My genset stayed mounted under the rig the whole time. The most fiddly part was replacing the main governor spring (it's pretty far back in there); the second most annoying thing was the struggle of manhandling the carburetor, the gaskets, the choke and throttle linkages, and the air filter housing all at the same time during carburetor removal and reinstall.

Thanks for the tips! Education is the most expensive thing in the world, but I still feel like I got a pretty cheap primer on small engine repair after it was all said and done. If you're in the same position reading this (old, poorly maintained Onan generator that is surging under many conditions), STRONGLY consider putting a new carburetor in it as your FIRST intervention. I'll hang around the forum to yell that at newbies 😄

[Straylight]

azrving wrote:
Read the plug. If you want to live with it as is and you see that the plug is more of a brown color you are pretty safe. If you were to see a black color it's an indication of a rich condition. Rich conditions can cause cylinder wash and fuel dilution. A white color could be on the lean side and cause higher temps and exhaust valve burning.

I'll pull the spark plug at your recommendation, too. Will report back. Might photograph everything, just for other people reading this thread for their gens in 2020 and beyond.

[azrving]

Read the plug. If you want to live with it as is and you see that the plug is more of a brown color you are pretty safe. If you were to see a black color it's an indication of a rich condition. Rich conditions can cause cylinder wash and fuel dilution. A white color could be on the lean side and cause higher temps and exhaust valve burning.

[Straylight]

Chum lee wrote:
I don't mean to be a smart *ss but are you having any problems running equipment with the genny? Any problems starting it, reaching maximum output, excess fuel/oil consumption, exhaust smoke, overheating, noise, spark plug fouling, etc? I have the same unit and I can't hear yours, but, mine does change speeds/voltage slightly depending on load, altitude, temperature, etc. It has never failed to do what I ask it to do. Years ago I learned not to try to fix problems I don't have and I spend my time resolving the ones I do. Could you be expecting too much? Just asking. You have a very popular genny. It might be worthwhile to listen to others and see what they sound like before you condemn yours.

Chum lee

I don't think this is a smart*ss point at all! It's really why I'm here: The thing runs, never pops down below 57 hz for more than a half second, and powers my A/C and microwave well enough; I'm curious if this is just how it's gonna be or if I should keep pushing it.

re: other comments, let me read it back to you guys:

• Two main suspects: Poor carburetion or poor governor springs.
  
• If it's the carburetor, I'll likely need to replace it, given that the interventions so far haven't yet fixed it (I tried carb cleaner and air, then a very Berrymans-heavy external gas tank over several days, then an ultrasonic bath). If I really wanted to, I could poke around in the carb with strands of small-gauge copper wire, but even that wouldn't guarantee anything.
• If it's the springs, I can replace them and redo the governor calibration, and I should see improvement.

I'm gonna do the following:

• Drop by the Cummins guys tomorrow and pick up the two governor springs (the main spring, short and fat, and the spring parallel to the throttle linkage, long and narrow) in addition to an air filter (worth a shot). Install same. I'm a little wary about how much of a pain it's gonna be to replace that main governor spring by reaching back into the genset from the access panel, still mounted under the rig. Any advice there?
  
• Redo governor calibration by: adjusting speed screw at idle to 62-64hz, checking that pulling throttle tang against stop screw drops hertz to steady ~55hz and genset doesn't die, applying heavy load and observing hunting pattern, adjusting sensitivity screw counter-clockwise by one or two turns to decrease sensitivity to eliminate any hunting condition, re-adjusting speed screw in light of new sensitivity screw position, lather rinse repeat until I observe a drop to 58-60hz under load with no hunting condition.
  
• And if none of that works I'm either gonna close the access panel and live with it, or I'm gonna put a new carburetor in it.

Quick edit: I'm also going to check the choke linkage and housing and starting-temperature setting. Possible something's wonky there, considering bad behavior on startup that subsequently evens out considerably after the unit (and thus the exhaust-heated thermostatic choke) has heated up.