Onan Carbs

[Mark_K5LXP]

Compare a muscle car from the early 1970's to a modern gutless 4-cyclinder small engine car

That doesn't apply here, because the 70's car didn't compensate for altitude. The 4K has an altitude adjustment and is spec'd for that. Your 4K altitude adjustment not working is a separate problem.

I am asking about normal use in an RV, not an industrial use.

RV's are not as tepid an environment as I think you perceive. I wouldn't call it industrial but certainly commercial. Maybe you don't operate one under corner case conditions but that doesn't mean no one does, or that you might at some point.

it is also the design that is poor.

It meets the spec. Just because it doesn't meet your design expectation is something else. There are many, many 4K's out there mine included that are working fine. You can't crap on the 4K design just because yours had a failure that was likely not a design flaw. If yours didn't have a carb issue or whatever I doubt you'd give running a 4K a second thought. Your A/C runs and chef boy-r-dee warms in the microwave from carb or EFI just the same. Read some of the user reviews of EFI inverter gensets on amazon. Many are 5 stars, they work great. A notable number are one star, the thing won't start and the dealer can't figure it out. I don't see a lot of distinction between a legacy fixed cam carb unit that doesn't start and an EFI VVT unit that doesn't start.

I wonder how well a new 4K Onan would do close to 3KW load at 7K' in reality despite Onan's claims.

Mine's parked right now but if you want I'd test it any way you come up with here at 5200ft. I've got a few resistance heaters I could plug in, the trick would be to measure volts, amps and frequency readily. It should come in at 4000 - (3%x5000ft) ~ 3400W. If it could do that I would expect it would track to commensurate higher altitude output.

Mark B.
Albuquerque, NM

 

[Adventurous Traveler]

In Minden, NV, which is south of Carson City?

Yep, that was it.

So why do the Onans cost four times the price of a new inverter genny? What is the big advantage of a non-inverter genny?

They're in RVs, my guess.

 

[DonTom]

Mine's parked right now but if you want I'd test it any way you come up with here at 5200ft.

Here in Reno, I am at 5K' and my genny works fairly well here. There is a very noticeable difference at 7K'. You could be right about my elevation won't adjust for that high, even though the label says 10K' at max. But it still runs too rich at 7K' even when set for 10K'.

But there is a lot more that can be done to help compensate for higher elevations than air fuel mixture, such as an air pressure sensor of some type. That's why I say the Onan's are an ancient design.

I am sure Onan meet or beat their own specs when new. But there is a lot of room for engine performance improvements and then they can have a lot better specs for higher elevations than they now have.

-Don- Reno, NV

 

[Larry N.]

I don't think anybody runs an RV genny for four days non-stop.

I have done so, more than once (Oshkosh during Air Venture week and FMCA International Convention in Tucson). And I have additionally run them for 12-16 hours continuously at least twice in one week on several occasions (start and end of Scout camp, for example). And I would expect any genny in an RV I had to be up to that chore repeatedly, even if I only needed that every couple of years.

 

[Mark_K5LXP]

there is a lot of room for engine performance improvements and then they can have a lot better specs for higher elevations than they now have

Of course they probably could, but that's not the issue you're having at 7500' running a non-stock carb. I would offer they meet the original spec as they sit, which exceeds 7500', despite how much better a different technology/topology might work. You're off in the weeds with a bad/wrong carb or other problem and no amount of wishing it was EFi will change that. Solve the problem yours has, and you too can enjoy rated performance* over their spec'd altitude range.

* - derated for altitude per published chart

Mark B.
Albuquerque, NM

 

[DonTom]

Solve the problem yours has, and you too can enjoy rated performance* over their spec'd altitude range.

Yes, I will be working on it when I get back to Auburn and then go up to the Donner Summit Rest Area (7,240' elevation) and test it out under a heavy load.

Onan specs say "Power output decreases 3.5% for every 1000 ft (305 m) increase" after their specs which are for 500 feet elevation. That comes to around 25% loss of capacity on my 4KW genny or around 3KW at 7,000'. So I will make sure I have just a little under a 3KW load when I do test it after I change the carb (but first to another Chinese carb as I do have two others) and do the valve adjustment. If I am not then satisfied, I will try a genuine Onan carb. But I find it ridiculous to pay the same price for an Onan carb as for a new inverter genny which probably has nothing but advantages for the way mine is used. IOW, I never use my Onan for more than a couple of hours at a time. Never have and I probably never will. I can keep it very simple by using my old Onan gas line to fill up an inverter genny gas tank manually, which I have already put a off/on shut-off valve on, so I can shut off the gas to the Onan (or fill a new inverter genny) easily.

So all I would need to do is remove my Onan and mount in an inverter genny with a wireless remote control in the same space and I can fill its tank as needed from the old gas line. Sure will be a lot easier to remove & work than an Onan and can be replaced for about the same price as an Onan Carb. I could even consider not mounting it at all, and even removing it when needed. I have many options. But first, I need to measure the room in there and figure out what will fit.

I do not see where duty cycle specs are mentioned anywhere for inverter gennys which makes me think 100% running all day and all night is probably okay, but that will not be an issue to me anyway.

I would like to find the best fuel-injected inverter genny that will fit my needs as well as fit in the same space as my Onan. I don't care much about the cost. The inverter genny can cost more than my Y2K RV is worth for all I care.

Over the years I have become a carburetor hater! Too many issues with them too often, IMAO-- and they never perform as well as EFI under varying conditions.

Another issue can be venting the inverter genny as a portable generator puts out around six times as much emissions as a car and people are killed by them every year from improper use, such as running them indoors during a power outage. Not everybody reads the warnings--and some people ignore them. I can almost understand that with the countless warnings on everything these days. "Excessive means the same as insufficient" --a Chinese proverb.

Based on some of my recent web searches, I am beginning to think CA is doing this stuff with the genny restrictions the correct way!

-Don- Reno, NV

 

[Larry N.]

Onan specs say "Power output decreases 3.5% for every 1000 ft (305 m) increase" after their specs which are for 500 feet elevation.

You might note that the spec is likely for a "standard atmosphere" which is, at sea level, 29.92 Hg", 59º F (15º C) and 0% humidity, with a 3.5º F (2º C) lapse rate (temp decrease) per additional 1,000 ft.

Basically that means that warmer temps leave you with less power than the spec would seem to indicate. The chart below shows that a 70º F temperature at 7,000 ft with the "standard" temp being 34º F is a very warm day, thus less power than the 75% you seem to expect.



This density altitude chart:




shows what the engine "thinks" its elevation is at various temperatures, so that at 68º F at 7,000 ft your density altitude is 9,147 ft, a tad over 30%, which is less than that 75% you mentioned. Higher temps will, of course, be worse.

Again, I don't think this is necessarily ALL of your problem, but is likely a fair share of it.

 

[DonTom]

You might note that the spec is likely for a "standard atmosphere"

I found it in writing somewhere that Onan specs their gennys at 500' elevation & 77°F (25°C). I will see if I can again find it ; so hold on . . . .

Here is that "somewhere":



The only way to not be affected by elevation and temperature is to not use an engine that requires compressed air to get its power--such as an EV.

However, some ICE designs will work much better than others at higher elevations. It is possible to compensate for a lot of it by advancing spark timing and that type of thing which Onan doesn't do.

-Don- Reno, NV

 

[rvlifer]

If a new inverter generator works for what you need and costs less have you considered switching and give up on the Onan? Sounds like the Onan is overengineered for your current needs

 

[DonTom]

If a new inverter generator works for what you need and costs less have you considered switching and give up on the Onan? Sounds like the Onan is overengineered for your current needs

I could consider both, fixing the Onan and buying a couple of EFI inverter gennys that I can connect together. What I would like is two 3KW EFI inverter gennys that can be configured for 6KW and 240 VAC as well as 120 VAC and have a remote and all that. But is such a thing made?

Anyway, I have a few ideas, but I will have to check things out in the morning, measurements and stuff like that. The Onan area is probably way too small, but perhaps I can convert the Onan area into a storage area and use the rear outside storage area (a lot more room) for the converter gennys and then run the Onan fuel line there. It already has a shut-off valve going to the Onan that I installed many years ago that I can use to fill the inverter genny tanks.

But until I change the carb and do a valve clearance adjustment and test at Donner Summit (7,240') with a load of around 3KW, I will not make any decisions. But I will probably be looking at a lot of inverter gennys until then. They sure make a lot of different types these days, but that doesn't mean they make what I want. I am not concerned about the cost, just if I can buy what I want somewhere.

-Don- Auburn, CA

 

[DonTom]

But is such a thing made?

To my surprise, YES!!!!

I wonder if it will be possible for me to install a couple of these in my Y2K Class C, which will be an overkill in more important ways to me.

"Two 120v generators are combined into a 240V generator using a dedicated series parallel box (the series parallel box is sold separately)"

"Fuel Injection Inverter"

Two of these with all of the above, but just a little smaller will be perfect for me. I do not need a total of 9,200 watts, but that will be fine if I have the room. A total of 6KW would be perfect in every way. And at 240 VAC I will be able to use them to charge my electric motorcycle near its full charging capacity.

The only issue can be the size of these things, and being able to put them somewhere.

But this should work a lot better than my Onan for my needs. Especially at the higher elevations.

-Don- Auburn, CA

 

[chuckbear]

We used a separate gas tank to run our Honda genset for a long time. Never had any problems. No reason why this wouldn't work for an RV. Here are the details, Extended Use Tank For A Honda Generator In 4 Easy Steps , Chuck

 

[DonTom]

We used a separate gas tank to run our Honda genset for a long time. Never had any problems. No reason why this wouldn't work for an RV. Here are the details, Extended Use Tank For A Honda Generator In 4 Easy Steps , Chuck

Thanks, but I wonder if there is a way to connect my Onan gas line to it. But even if I have to fill the genny tanks manually from it, that is not much of an issue to me.

I just discovered this genny cost much less than I expected. Only $900.00 each on Amazon. Plus the cable--whatever its price tag is. So perhaps a total of around 2K$ and sounds so much better than the Onans to me.

Not legal here in CA, but I can ship a couple of them to my Reno house. I will most likely order this setup even if it doesn't end up in my Y2K RV. But I expect they will get very little use if not in my Y2K Class C.

-Don- Auburn, CA

 

[Isaac-1]

To a degree you get what you pay for on these small inverter generators, I have a Honda EU1000i (950 running watts, weighs 29 pounds) that I bought in 2005 for about $600, current price is about $900, as well as a Champion open frame 7,500 watt tri-fuel inverter generator that I bought last year for $1270 on sale, and I can tell you that while the Champion works ok, there is a world of difference an apparent build quality between the Honda and the Champion, of course the similar size Honda sells for $4,000

 

[DonTom]

I can tell you that while the Champion works ok, there is a world of difference an apparent build quality between the Honda and the Champion, of course the similar size Honda sells for $4,000

Why would I need better than "ok" if it works well for me? I am sure the Honda will be quieter and better built than the Champion, but can it do what I want such as 240 VAC and work better than a carb at higher elevations? And will the Honda last three times as long for more than three times the price? OTOH, if smaller and lighter, that could make a big difference.

I am far from being done with checking out inverter gennys. There sure are a lot of them available these days. And I do not care about the price if I find the perfect genny or gennys for my RV. So I will certainly check out the Hondas as well. There is no hurry on this end.

I wonder why they are not normally put in new motorhomes, since they are cheaper than Onans and should be fine if not better for what most RVers need. While I consider Onans to be well built for heavy continuous duty, their design is ancient, IMO. It sure would make a lot more sense than the tankless water heaters they have been putting in the new motorhomes lately--which I got stuck with in my 2022 Class A.

For now, I will be working on my Onan. I will perhaps start on it right after I post this message because it looks like there is a break in the rain. I rushed here from Reno yesterday after looking at the weather report for the Summit. No chance of snow yesterday but heavy off & on snow for the next week or so.


-Don- Auburn, CA

 

[DonTom]

I will perhaps start on it right after I post this message because it looks like there is a break in the rain.

That didn't last long. It started to pour rain by the time I could get outside. And it will soon be getting dark.

I am not working on the Onan today.

88% chance of rain tomorrow (Friday), 97% for Saturday, 0% on Sunday and 91% on Monday.

So it looks like I could need to wait until Sunday. Good thing there is no hurry.

-Don- Auburn, CA

 

[rvlifer]

Why would I need better than "ok" if it works well for me?

You sound like Henry Shires lol

 

[NY_Dutch]

If you can find a knowledgeable Onan tech willing to do it, some RV models can be converted to 120/240 with some relatively minor rewiring.

 

[DonTom]

Looks like the 240 VAC cable is out of stock for the Champion GM4600iAEFIC.

But here it is.

And with a 14-50R!

-Don- Auburn, CA

 

[DonTom]

If you can find a knowledgeable Onan tech willing to do it, some RV models can be converted to 120/240 with some relatively minor rewiring.

IIRC, my Onan is not one of those that can be converted to 240 VAC. Besides, I would want more wattage than my Onan is capable of because I may want to use it to charge my electric motorcycle at around 6.5 KW.

-Don- in rainy Auburn, CA