Onan 4000 Generator not quite starting - Probably a fuel issue

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ziplock

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The opposite. Going up in altitude will richen a mixture. Turning it higher altitude correction will lean it.
Is there somewhere I can read this information.

I'm trying to understand richer and leaner and this thread is confusing me.

Thanks.
 

Larry N.

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udidit is correct. Richer and leaner is relative to the desired mix of fuel and air going in to the engine for combustion. Richer means it has more fuel for the amount of air, while leaner means the mixture has less fuel for the amount of air.

Light (piston engine) aircraft MUST deal with this as they change altitude, and MUST lean the mixture as they go higher, since the air is less dense, thus there is less air pressure (thus less oxygen). Too rich a mixture (or too lean) starts messing up the internal combustion (each in different ways) and can cause problems, perhaps even engine damage, depending on the conditions.

Todays ground vehicles generally take care of this with the programming of the engine computer, but some engines (most piston engine aircraft, lawn mowers, generators, etc.) don't have a computer so must use the techniques that were appropriate 30 years ago and more.

Addendum: You can search the web for "rich fuel mixture vs lean" and get lots of info.
 

udidwht

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So if you set the dial for a higher elevation, you get more fuel versus air?

@Larry N.
It (dial) will increase and/or limit fuel only. The fuel is fed via a jet.

Aircraft use a mixture lever to increase or decrease the fuel. LOP or ROP (lean of peak or rich of peak)

Peak being 14:7 stoich the hottest zone is 14-15 under load/WOT (Wide open throttle). At cruise in an aircraft one can lean out the mixture to as lean as 17:1 or so (light load). This can also be done in a car but you need added advance to burn the lean mix. Load = throttle position.

A 16-17 afr under part throttle condition is also cooler running than say 13:1 under same part throttle condition.
 
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ziplock

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It (dial) will increase and/or limit air only.
So, if I turn the dial to a higher elevation, it will let in MORE air? And more air means leaner? Or is it richer?

Please tell me it finally sunk in this brain.
 

DonTom

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Auto-reset?

So, if I turn the dial to a higher elevation, it will let in MORE air? And more air means leaner? Or is it richer?

Please tell me it finally sunk in this brain.
There is less air at higher elevations. So, engines run richer (more gas, less air). So, the carb needs to be set more lean (less gas, more air) to compensate for the higher elevation.

But when I don't think it out, I can get confused as I did in that other post. Setting the carb for a higher elevation will make it run more lean.

-Don- Auburn, CA
 

ziplock

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-Don- Auburn, CA
Okay.
I copied one quote. The person changed it. My copied quote still has the old sentence.

Read carefully to see what I mean.

Maybe a new thread with correct information and nothing muddying the waters would help.

That elevation knob needs explained.;)
 

DonTom

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That elevation knob needs explained.
It simply changes the ratio between the gas and air. Usually, 14.7 parts air to one part gasoline is desired at any elevation. If the carb is set for a higher elevation, it supplies less gas into the carb to make it leaner.

It takes a richer mixture than that 14.7 to start an engine. That is what the choke does. Won't need as much choke, if any, at a higher elevation because it will be richer up there even if nothing is changed.

-Don- Auburn, CA
 

Henry J Fate

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Okay.
I copied one quote. The person changed it. My copied quote still has the old sentence.

Read carefully to see what I mean.

Maybe a new thread with correct information and nothing muddying the waters would help.

That elevation knob needs explained

What happens to the air and fuel mixture in a combustion engine as elevation changes is a little confusing but can be understood in very simple terms.

As you increase in altitude, you should decrease your fuel supply.

This rule is always a factor and is a direct result of a lower atmospheric pressure and air density as altitude increases.

Your Onan carburetor adjustment should have altitude increments for your dial setting.
 

Ex-Calif

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Reading through the above I can see how things get confusing - let me try...

The carburetor has a fixed throat diameter. Between the carb and the engine is a butterfly valve connected to the throttle. The volume of air entering the engine is directly related to how far the butterfly valve is open.

At sea level there is about 14.7 psi of air pressing down from the atmosphere. As you go up in altitude the pressure gets less and less. That's why humans have to start using oxygen above about 12,000 feet. Even through we suck in the same "volume" of air in our lungs the density of the oxygen is less - i.e. Molecules of oxygen vs other gases.

At the throat of a carburetor is a small orifice for the fuel. As the air passes this orifice it draws in fuel due to the lower pressure in the carb throat. But the density of fuel doesn't change at altitude. So if things weren't adjusted there would be the same fuel for less oxygen - i.e. the carb would be very rich.

So the adjustment to a carb is a needle screw that limits the amount of fuel. Once adjusted for altitude the generator will run clean and properly. But as you can imagine if the generator were moved back to sea level there would be denser air again but the fuel would then be insufficient and the mixture would be too lean at sea level.

What the pilots are telling you and us is that airplanes have a "mixture" control and they can adjust the mixture at any time through a control in the cockpit and that's how planes handle the changes in altitude.

Fuel injected engines and supercharged engines operate completely differently than a simple carbureted engine.
 

Larry N.

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So if you set the dial for a higher elevation, you get more fuel versus air?
Less fuel, as others mention above.

Fuel injected engines and supercharged engines operate completely differently than a simple carbureted engine.
While that's a true statement, I'd like to clarify that rich or lean still has the same meaning, that is, the ratio of fuel and air.

And I'd note also that the elevation knob is a form of mixture control, but not designed (or needed) for periodic use during the "flight" in the RV the way aircraft mixture controls are (they're typically adjusted several times in one flight because of altitude changes during flight, sometimes even before flight).
 

Ex-Calif

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>>Fuel injected engines and supercharged engines operate completely differently than a simple carbureted engine.<<

While that's a true statement, I'd like to clarify that rich or lean still has the same meaning, that is, the ratio of fuel and air.

Yes the fuel injected and supercharged engines still have to deal with changes in density but they do it in different ways. Trying to keep this simple as relates to RV generators.
 

Mark_K5LXP

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The problem of mixture over altitude, or a least a good part of it, was solved on motorcycles decades ago through the use of constant velocity carbs. Maybe not as tightly controlled as closed loop fuel injection but around here where you can see a change in elevation of 5000 feet on a scenic lunch trip, I would see the guys with the fixed jet butterfly and slide carbs popping and blowing smoke going over the passes where mine would only suffer a bit of power loss. Guessing the additional complexity of a CV carb doesn't warrant the cost when installed on a generator but it would certainly minimize confusion and manual adjustment.

Mark B.
Albuquerque, NM
 

Old Paint48

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My Onan 4000 gas generator sounds like it is starting, but it immediately dies as soon as I release the starter. I am barely beginning the process of introducing myself to the generator since acquiring this MH. I have no clue how long since it ran last. I know the basics about gasoline engines but have no manual for this specific generator.

I primed it by pressing the prime button (it apparently has an electric fuel pump). Gas dripped ( have plenty of fuel in the tank). I think it was from flooding and not a leak. I removed the air filter and gave it a shot of starting fluid. It started for a few seconds with black smoke (I assume because it was flooded). This means it is getting spark though the outside of the sparkplug looks OLD. It could be original since it has less than 200 hours of runtime.

I will pull the spark plug today to see what it looks like. I will see how difficult it is to drop the sediment bowel and check for trash, water, or a stuck float. I guess I could shoot some SeaFoam carb cleaner in it. I guess I will search online for a manual.

I have no idea what the altitude adjustment is. I assume it changes the air mixture. It was set at 10,000 ft, and we are at less than 100 ft sea level.
I had similar proble
My Onan 4000 gas generator sounds like it is starting, but it immediately dies as soon as I release the starter. I am barely beginning the process of introducing myself to the generator since acquiring this MH. I have no clue how long since it ran last. I know the basics about gasoline engines but have no manual for this specific generator.

I primed it by pressing the prime button (it apparently has an electric fuel pump). Gas dripped ( have plenty of fuel in the tank). I think it was from flooding and not a leak. I removed the air filter and gave it a shot of starting fluid. It started for a few seconds with black smoke (I assume because it was flooded). This means it is getting spark though the outside of the sparkplug looks OLD. It could be original since it has less than 200 hours of runtime.

I will pull the spark plug today to see what it looks like. I will see how difficult it is to drop the sediment bowel and check for trash, water, or a stuck float. I guess I could shoot some SeaFoam carb cleaner in it. I guess I will search online for a manual.

I have no idea what the altitude adjustment is. I assume it changes the air mixture. It was set at 10,000 ft, and we are at less than 100 ft sea level.
I had similar problems a few years ago...on yours first thing Id do is clean that spark plug and contacts, then turn down that elevation to sea level... if that doesnt work, on mine I removed the carburetor ,removed the bowl, turn out the needles counting how many turns each one and log so you can put them back in reverse order if you have a float be careful not to change its angle, after cleaning all with sea foam.. take pictures before you remove anything so you can put all linkage back the way it belongs.....OP
 
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