🧀 Generators on Natural Gas

Anyone here well versed on fuel conversions for generators?

I converted a couple of hondas to NG but see some decrease in max power. Wondering how to get the max back up.

Check the water column and pressure? I’m pretty okay with LP but not so much with natural gas. Could be an issue with the orifice not being large enough?

Just had a discussion on this today with a client converting from LP to natural gas on a generator.

If your utilities are down, you have the LP stored for your generator. Food for thought.

How gunked up are your cylinders?

Orifice was specially made for NG… it’s different than the one I used for propane. I have a water column gauge in my Amazon cart but I have not bought it yet. I need to do that. It’s probably the 25 ft 1/2 hose I’m using to feed two 3.5 hp generators. It’s longer than I need but my 10 ft hose was too short. Got a 15 ft 3/4 inch hose in my cart too. Will likely order someday. In the mean time, I can use gasoline if I really need full power. Or I can change the orifice back to propane and use that.


less than 2 hours total running on gasoline. So… unlikely it is that.

I have a gas standby generator but I’m considering buying a newer dual fuel jenny with electric start. I’m too old to be yanking on a pull cord!

I like the idea of propane. Doesn’t produce the same power as gas, but is infinitely easier and safer to store.

I assume that you know most of this being that you are some kind of engineer. Possibly I will touch on something here that you have not thought of.

The energy density of gasoline, NG, and LPG are different. The cylinders of your (I assume) piston engines have a specific volume, compression ratio, and intake/exhaust efficiency. As I do not know if your system is carb/FI, or Direct Injection, I will speak generally.

Since generators run at a constant speed under full load, this is easier to achieve than in vehicles.

The key to maxing out the power is to ensure that the fuel charge each cycle, and the accompanying oxygen are matched and maximized. I would suggest:
1 Check that the gas feed pressure at the carb is at spec, this should be on a fully warm engine.
2 Check that the air cleaner is clean, and not blocked, and that any enclosure of the generators have the needed ventilation.
3 Double check that the “orifice” is correct. Jetting is an art.
4 Assuming this is not a diesel, run for 6hrs-2days and check the electrodes on spark plugs. There are many resources online for determining lean/rich/optimal mixtures in internal combustion engines.

As stated, I have been impressed out here with your engineering/tech acumen, and only intend to share thoughts not insult your intelligence.

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Excellent advise and well written as always :+1:

With a conversion kit, sometimes the wrong orifice can be sent. There should be a number on it. I would add to make sure it is correct by checking the manual for the # and the # on the actual orifice if you’ve not already done so.

Ok thanks everyone. I got it from here.

Can you let us know what the fix turned out to be? I’m curious…

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I’ll update the thread as I work on it. It’s a little project that has taken months as I find an hour here and there to work on it.

First of all, buy a Generac. LP - Natural Gas is very clean, and stores well ( doesn’t degrade ). Diesel would be next. Gasoline as a last resort. ---------------------------------------------------------------------------------------------------- [

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Thanks. Considered it. Got friends and neighbors who recommended it. In the long run, cheaper than my solution of multiple smaller units too. But … I chose otherwise. Smaller ( meaning, within my weight carrying limit), redundant (meaning soft operational degradation as failures occur), tri-fuel units (meaning I have options if fuels become unavailable) was the solution in my trade study. Plus I have constraints imposed by my significant other that also drove me in that same direction.

Other than those factors, the Generacs designed for and running on NG and mounted on a concrete slab with an auto start and connection to a transfer switch is certainly a nice professional solution.

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I will lay a slab & house the generator in it’s own metal ( lockable ) shed; but I’ll check with the manufacturer to be sure it can be in an enclosed structure. Just for a bit more security. All the wiring & fuel lines will be run underground in heavy schedule 80 PVC pipe. I don’t want the unit right against the house. Maybe 15 or 20 feet away. Possibly a chain link fence ( covered with wisteria ), around the structure. I am always inclined to over engineer projects; as long as the engineering is simple. I have 1/4 acre in the middle of town, and other than the large garden, I see no reason to not take advantage of the space. For the garage - workshop, I’ll just use the small unit I already own. A Honda I bought at a yard sale. 2,000+++ watts & 18 amps; but gasoline.

Thank you.

Note for anything long term and few usages, look for no-ethanol gas. It works wonders.

Not much of an update. But was going to order some test equipment to see what the pressure is at a couple places in the line. A flow rate gauge would be better but delta pressure per unit length and hose diameter and NG characteristics would give me that.

Instead… heck with it… just ordered a bigger and and shorter hose. I’m sure I’ll still need some fine tuning of the fuel system but at least the flow rate that can be delivered won’t be in question.

Also… did some reading on the big “demand” regulators I have. Duh… I finally realized they are simply on-off valves that are actuated with the vacuum. It seems to be binary… on or off.

One more thing. While I am slowly working this problem, I went back to gasoline since we are in the middle of a big freeze and could lose power if we get ice. Wow… those little 2200 watt hondas purr like kittens on gasoline. I want them to sound that sweet on natural gas. Still, I want the system to be tri-fuel so I might have to accept compromise.

Great update, thank you!

I went back to gasoline since we are in the middle of a big freeze and could lose power if we get ice. Wow… those little 2200 watt hondas purr like kittens on gasoline. I want them to sound that sweet on natural gas.

For some reason that made me LOL… Probably because I can appreciate the different noise levels generators can make.

These are nice. I’d give numbers but it is all relative to some distance and power load, etc. The nice thing about these inverter generators is that 1) they have a mode that is essentially idling but will automatically ramp up as needed (these Hondas are fast enough to provide for a furnace motor turn-on. My 2000 Watt Wen generators struggle a bit.), and 2) when you connect them to get twice the power, you only get twice the noise. Having looked at more powerful generators, it seems that you get more than twice the noise from every doubling of power… all else being equal.
In my world of electromagnetics, we would expect just that from noise sources and would attribute it to the difference between coherent vs non-coherent sources. Not sure I’ve ever seen a similar analysis in the mechanical world of engines but some similar phenomemon seems to be at work.

Also… reviewing some factory made tri-fuel generators, I’ve come to expect that I will have to give up power when running NG. Those factory made tri-fuel generators lose about 20% on NG. I can live with that for the benefit of never having to go buy tanks of propane or gallons of gas so long as I have NG. I have another generator and a conversion kit to to make up the difference. So I hope to get no more than 20% loss when I get my larger hose.

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Can’t believe I’m “excited” about getting a 3/4 inch gas hose. :slight_smile:
But I am.

One of the things that bothers me, as an engineer, is how some things are named according to a measurement… but they are not really that size. Like a 2x4 is not actually 2 inches by 4 inches. Grrrrr…
Likewise, gas hoses and pipes are sloppily named as well… the manufacturers of some 1/2 inch hose and pipes make no effort to make it with an inner diameter of 1/2 inch…about all you can count on is that it is likely smaller than 3/4 inch and larger than 3/8 inch. Another grrrr.

And also, I’m finding that hoses will be advertised with BTU / hour flow rates with some assumptions about pressure and pressure drop. But you can use these hoses for low pressure propane as well as natural gas. But the BTU /hour rates will be different because a cubic foot of natural.gas has less energy than a cubic foot of propane. Densities are different too. So there is alot of guessing on my part as to what these hoses can deliver.