Onan Carbs

[DonTom]

The stock Onan Carburetor has both an idle jet and a main jet, as to performance I have used my Onan KY 4000 with genuine Onan carburetor at over 7,000 feet in the past, this includes running daily at the south rim of the Grand Canyon circa 6800 ft, as well as in Yellowstone, as well as one forest service campground at 8,200 ft, though power output was very limited.

Around how many KW of load before you have problems at 7K feet elevation?

-Don- Reno, NV

 

[Utclmjmpr]

Doesnt your carb have an air correction setting for altitude??>>>Dan

 

[DonTom]

Doesnt your carb have an air correction setting for altitude??>>>Dan

Yes, but it doesn't help. Even if set for 10K' elevation, it runs very rich at 7K' and that is probably the problem when the genny is loaded. When not loaded, it still is more difficult to start and sometimes floods. However, I do not have any of these issues at lower elevations. At 2 or 3K feet elevation, it runs perfectly even with a heavy load, never dies, and starts up in a second or two of cranking.

-Don- Reno, NV

 

[Isaac-1]

Around how many KW of load before you have problems at 7K feet elevation?

-Don- Reno, NV

I only really noticed being down on power at 8,200 feet, as I could not run the air condition and convection oven at the same time. As these are both fairly large loads all I can really say is the issue was somewhere between about 1,500 and 3,000 watts.

 

[DonTom]

I only really noticed being down on power at 8,200 feet, as I could not run the air condition and convection oven at the same time. As these are both fairly large loads all I can really say is the issue was somewhere between about 1,500 and 3,000 watts.

At 1,500 watts is probably about where my genny gets flakey at 7K feet elevation. My electric motorcycle draws 1,400 watts and while I could still charge it, genny would die often. I did not need to charge from the genny there anyway, it was just for a test. My converter was charging close to 300 watts, but I could either unplug it or charge the bike after the battery was fully charged and not drawing any current. But was flakey (but still useable) as low as 1,400 watts total.

Besides the carb mixture, do you think a valve adjustment can help with higher elevations? I realize nothing can help to get all the power back at higher elevations. Perhaps a valve adjustment will give me more power at all elevations. I doubt it has ever been done on my Y2K genny. I will do it in a few days when I am back in Auburn. So far, I only removed the valve cover gasket.

-Don- Reno, NV

 

[Isaac-1]

A valve adjustment may be a good idea, the service spec is to do valve adjustment every 500 hours

 

[Adventurous Traveler]

Regarding vehicles today and the amount of plastics used, I believe a lot of that has to do with the MFG trying to reduce as much weight as possible wherever possible to respond to tougher MPG standards put on them.

Funny about the Briggs carb. I did the same thing on my old lawnmower. A new Briggs carb was $169. I paid $139 for the whole mower at Walmart. I bought a knockoff on Amazon for under $20.

During our West Coast trip two years ago I had no problem with my Onan 5500W genny at elevations exceeding 10K feet. Spent 3 days in Reno Don, and loved it.

 

[DonTom]

I had no problem with my Onan 5500W genny at elevations exceeding 10K feet.

But at how much of a load? The Onans often run fine at high elevations until you put a heavy load on them, such as 75% of their max spec., such as around 4KW load on your 5.5 KW genny. But my 4KW genny cannot even handle 2KW at 7K' elevation.

Spent 3 days in Reno Don, and loved it.

Where did you stay in Reno? Many places to choose from.

-Don- Reno, NV

 

[DonTom]

There has to be a pretty large market to make counterfeiting these things worth the trouble.

Reminds me of what happened to oil filter prices for my 1971 BMW motorcycle in the early 1980s. BWM got greedy and tripled their prices on their oil filters. Then an aftermarket company started making the same filters at the same quality (couldn't tell any difference by looking) at less than half the price. BMW could no longer sell any of their oil filters.

So BMW lowered their oil filter prices even lower and put the aftermarket company out of business. Since then, BMW has kept their oil filter prices somewhat near reasonable.

-Don- Reno, NV

 

[garyb1st]

It's been about 3 or 4 years since I installed a carburetor in our Onan 5500. Got if from Amazon for about $55.00. Looked just the the one it replaced and has worked quite well since. Have had some issues recently but think they may have been heat related. Vapor lock possibly. Don't recall issues at higher elevations but do recall adjusting the elevation setting so it's possible.

Don't know if the smaller 4000 units are more costly but I'd never pay $500-$700 for a factory replacement without trying the cheap knockoff.

 

[Larry N.]

The Onans often run fine at high elevations until you put a heavy load on them, such as 75% of their max spec., such as around 4KW load on your 5.5 KW genny.

You must keep in mind that as normally aspirated engines increase in elevation they have a reduction in max power available. For example from the "Cruise Performance Chart" of a Cessna Cardinal RG (because it's handy to me) at 2500 ft the max horsepower available under "standard conditions" at 2500 RPM is 79% of its 200 HP engine, at 7500 ft is 72%, and at 10,000 ft is 66%.

In other words, it cannot produce as much of its horsepower (therefore cannot provide full sea-level load) at higher elevations as it does at sea level. While it may not be the complete answer, this is at least part of your problem, Don -- these Onans are not super/turbo-charged so lose performance with less dense air.

 

[DonTom]

You must keep in mind that as normally aspirated engines increase in elevation they have a reduction in max power available.

Yes, I realize there is nothing that can be done to make up for rarefied air, as then there is less compression. But I would expect more than 50% of capacity at 7K', even for an anciently designed Onan genny. IIRC, a 4KW Onan genny is spec'ed for 3.5KW continuously at sea level so I would expect better than 1.75 KW capacity at 7K' elevation and I am getting less power than that, or around there at best, with a lot of needing restarts.

No doubt this loss would not be anything like this if Onan had modern technology with fuel injection & air pressure sensors, etc. With my 1984 Venture motorcycle, I cannot even notice any difference as I climb up a hill at 9,000' elevation, and is not even fuel injected. But it does have an air pressure sensor and CV carbs unlike the Onan which is around a 1950 design, IMO. Even my BMW motorcycle came with CV carbs back in 1971. But even the genny in my 2022 Class A has a manual elevation adjustment. IMO, that is ancient nonsense for 2022. And their junky 1950-designed carb is extremely expensive. But my elevation problems are with my 4KW genny in my Y2K Class C.

I have not yet tried out my 2022 Class A Onan genny at high elevations. But I can tell you it has its own set of poor design issues, such as I mentioned here.

-Don- Reno, NV

 

[Isaac-1]

I am not sure about the Onan RV generators, but their commercial models include a power derating chart with altitude corrections in the operators manual

 

[DonTom]

I am not sure about the Onan RV generators, but their commercial models include a power derating chart with altitude corrections in the operators manual

I think I have seen one somewhere for my genny. I mentioned this high elevation issue a couple of years ago here, so let me check if that is where I saw the chart . . .

Here is that message. But not for the Onan, but for general use.

So I should expect 70% of my power at 7K'. But I assume this chart does NOT take into account the ancient design of the Onans. But I assume I should at least get 50% at 7 K' elevation.

-Don- Reno, NV

 

[Larry N.]

Yes, I realize there is nothing that can be done to make up for rarefied air, as then there is less compression. But I would expect more than 50% of capacity at 7K', even for an anciently designed Onan genny. IIRC, a 4KW Onan genny is spec'ed for 3.5KW continuously at sea level so I would expect better than 1.75 KW capacity at 7K' elevation and I am getting less power than that, or around there at best, with a lot of needing restarts.

Which is why I said:

While it may not be the complete answer, this is at least part of your problem, Don -- these Onans are not super/turbo-charged so lose performance with less dense air.

 

[House Husband]

Given there probably isn't an idle circuit I'd expect a single main jet right in the middle of the fuel bowl pickup. If you're motivated you can take any jet and silver solder the hole shut then re-drill with whatever diameter numbered bit you want to try.

Mark B.
Albuquerque, NM

Mark, main jets are honed or reamed or lazar cut. A drill bit will leave a rough surface that won't meter properly.

Richard

 

[Mark_K5LXP]

The engines I made jets for were not discriminating. In a perfect world you'd run it on a dyno and have an OEM jet kit to dial it in. As a broke kid fixing up trashed metric bikes getting it to not foul plugs and backfire was a win.

Mark B.
Albuquerque, NM

 

[DonTom]

As a broke kid

IMO, those were the good and fun days. Like when I used to go to the local dump yard to rob tubes and other parts from old junked TVs so I could go home and design & build my ham radio transmitters.

Now it is just too easy for me to buy everything I want, which will be much better quality than anything I can build. Better stuff, but all that takes a big part of the fun away.

73, -Don- AA6GA/7 Reno, NV

 

[Adventurous Traveler]

Where did you stay in Reno? Many places to choose from

Carson Valley RV Resort and Casino. For $55 a night, we had the benefit of a FHU site, casino, and amenities. The bonus was being a 20-minute ride over the "hill", err Sierras to Lake Tahoe.

I had my 1974 900 Kawasaki re-jetted on a dyno after the stock 4 pipe exhaust rotted out and I switched to 4-in-2 headers. Power increased on the dyno from 80 hp stock to 105 hp on the dyno.

I used to buy oil filters from Kawasaki until I found that Fram had a cross-referenced filter that was less than half the price of the Kawasaki filter.

Regarding Onan using "old" technology carbs on RV-supplied generators, that seems to be the norm of the RV industry in general.

 

[Mark_K5LXP]

Carbs - Guessing it's a legacy/regulatory issue. The design is stable, manufacturing in place, regulations grandfathered or crafted to exclude the status quo. To change anything would be a major disruption for sales, support, dealers, repair and end users. At some point the ship will sail, either the models are sunsetted or obsoleted and something else fills the space. But this is a far greater reaching product than RV's with a giant deployed fleet spanning decades (millions?). Perfection is the enemy of good enough. I would rather deal with a finicky mixture on a carb than pay a dealer to fix an inop fuel injected computer controlled wonder machine. No question the FI engine/inverter gensets will likely work very well, until they don't. Then we'd hear kvetching on the forums from users about dealer-only, very expensive repairs and maintenance. And, with CARB's recent generator ban it won't matter if it's FI or carb anyway. Enjoy your microquiet 4K's while you can.

Mark B.
Albuquerque, NM