I'm going to build a shed to put my generators in.I was thinking of putting a shelf over them and using
6-12 gallon marine fuel tanks with quick disconnect fuel line hooked straight to the carb.Is there any downside to this?

If there are any leaks the gas will spill straight on the floor.  One spark and poof!

Also, make sure the shed is properly vented.  I used one of those igloo type dog houses to cover the gennys and put a 12 volt fan to circulate air.  You don't want the genny to overheat.

Wouldn't this happen also if there was a leak in the regular generator's gas tank?
There will be openings in the walls next to the generators with fans and openings in the gable ends.

Yes, but in that scenario the generator manufacturer takes the risk and responsibility. Once you modify it all of that falls on you.

Why not put the tank outside and run it through the wall?

Besides the cautions of leaking mentioned, I see no real advantage to place 48-96 pounds of fuel on a shelf!  
I see nothing wrong with it other than getting it there by yourself might be a PITA!

I might place the container outside the shed and put the hose through the wall to save space inside.  You do not need the height to feed the fue by pressure; the same level should be just fine.

Bill

I don't see a substantial issue.  Use quality components.  Marine fuel tanks are pretty durable and are not prone to leakage.

I run my 3500W conventional Honda and 2200W chicom inverter with remote fuel tanks...  the Honda uses a direct siphon system once the line is primed with the squeeze bulb so you don't have to hot fuel the tank, but is not permanently connected... just insert the pickup tube in the elevated supply tank.... the inverter has a fuel pump, so I plumbed a "T" with an external fitting to the squeeze bulb tank between the pump and the fuel shut off... the supply tank can be at the same level as the inverter, only have to prime the line

As previously mentioned, some generators are equipped with a fuel pump.

The rest are gravity-fed - which means that your fuel tank has to be located above the engine in order for gravity to feed fuel into it.

However, don't go overboard on the fuel tank height - It also affects fuel pressure, which can make the engine run rich.

Also, note that your fuel tank MUST be vented to the atmosphere - Otherwise, a vacuum will develop it inside as fuel is consumed, eventually starving the engine for gas.

The height above the generator would be no more one foot,I don't think that wouldn't be to high would it.
The boat tanks are vented to the atmosphere.

Already have 2 gas generators

Unfortunately they're different wattage ratings and manufacturers.

I have a smaller diesel generator but is has gotten hard to find reasonably priced diesel generators on the market.

Personally, if I needed to replace my larger generator, I’d buy a similarly sized gas generator and then convert it to propane. The OP could convert his generators to propane and then hook them up to 100 lb tanks placed outside.

If the OP wants to use gas in boat tanks, there’s nothing wrong with his plan though. It’s highly unlikely he would ever have any leaks.

The issue isn’t how likely he is to have a leak, it’s the catastrophic consequences if he does.  The likelihood of the earth being hit by a giant asteroid is remote but when it happens everybody dies.

For the record, I think storing 72 gallons of gasoline over running, hot, vibrating generators is a very bad idea.

There is risk vs reward. If the risk is high and the probability is high....I won’t take that chance. If the risk is high but the probability is low, I’d say it’s worth it.

Nothing is risk free. Think about this.....where do most generators on the market store their fuel while it’s running? Right on top of the engine and MUCH closer than the OP’s planned location to the hot running engine.

Have you ever looked at a plastic 6 gallon boat tank? They are well built. They don’t want them leaking on the water and leaking fumes into the boat bilge. So, they are very safe tanks.

Comparing storing gas in boat tanks above the generator to an asteroid strike is pretty silly.

I didn’t compare an asteroid strike to a gas explosion.  Apparently the threat of a large gasoline fueled explosion wasn’t enough to make folks think twice about this so I used an asteroid strike as an extreme example to illustrate the point that sometimes it’s not the frequency of an event, but the severity of the consequences that matter.  

Yes, I’m familiar with marine auxiliary fuel tanks.  I guess this is another case where it’s not the obvious that’s the issue.  The tank itself may be fine but the use of an auxiliary fuel tank also requires hoses and fittings to connect the fuel tank to the generator.  Lots of bits and pieces to make it work mean lots of potential points of failure.  Throw the heat and vibration of running generators in close proximity to all this and the potential for a problem just goes up.  

An auxiliary fuel tank setup is not at all comparable to the integral tank of the generator.

So, now you are criticizing all external fuel tanks. That makes no sense. A generator uses a hose from the carb to the existing tank. An external tank uses a hose from the carb to the external tank. The parts needed to make an external tank (any external tank) work are identical to the parts needed to make the built in tank work. The only extra part might be a fuel filter add on to the line if the generator uses a filter inside the tank. If the generator uses an external filter the parts are the same.

The potential for risk with the OPs plan is so low there is nothing to lose sleep over. I think most people who don’t like the idea are getting their heads wrapped around the idea that fuel COULD leak down onto the generator and catch fire. Well the built in tank could just as easily do the same. A NATO can with a fuel withdrawal assembly could leak sitting near the generator and if it did, it would catch fire too. A gas can just sitting in the shed could also leak and if it did, you’d have a fireball too. Or, an asteroid could hit the shed and the OP would have a fire too. Either way, there is always risk to running a generator. There’s risk to just having electricity. Many people are killed every year due to electrocution. And yet, we all have electrical outlets scattered throughout our houses and don’t give them a second thought.

The OPs plan will work fine and if built correctly, it will never cause him any issues.

There is a little confusion going on here,it's not six twelve gallon tanks it six gallon or twelve gallon tanks.
So maybe 24 gallons for the 2 generators and I'll have enough room to put the tanks off to the side so, if there is any leakage it won't leak onto the generator.

Sounds like a decent plan to me. 6 gallon tanks will be much easier to handle since they are meant to be carried around. The 12 gallon tanks are meant for permanent installations.

I’m not criticizing all external fuel tanks, I use one myself.  I’m saying mounting your external fuel tanks over the running generator is a poor idea.  It’s a poor idea because things occasionally go wrong and by mounting the fuel over the generator you’re introducing a risk (fuel pouring onto a hot generator) that doesn’t need to be there.  It’s not the external tank I have a problem with, it’s where the OP wants to put it.

The setup for an external fuel tank is not identical to an internal tank.  There are more fittings, almost certainly including quick disconnects, much longer fuel lines (by feet), in-line filters and squeeze bulbs each requiring their own fittings.  All of this is pieced together from parts from multiple manufacturers by someone who may or may not be entirely comfortable doing it.  Compare all that to the short length of fuel hose inside the factory built and engineered generator.  There is no comparison.

You’re right about one thing, there is risk in running a generator.  That’s why it’s worth making the extra effort to set it up the best you can and that includes safety.  Introducing a risk that doesn’t need to be there just isn’t a very good idea.

Thanks for clearing that up.  I agree with Colt’s suggestion of going with the smaller tanks, they’re much easier to move around.

When I had a quick disconnect fail on me a few years ago I came on here and asked if anyone knew of anything better than the plastic connectors everyone uses.  Some very helpful people pointed me to Tohatsu quick disconnects, which are available in chrome plated brass.  I’m not telling you it’s what you have to use but take a look and decide for yourself.  Good luck.

 

for hurricane Irma, I stuck the 3500W Honda on a small utility trailer behind the John Deer mower (an 1 7/8 hitch ball on the mower) so I could keep two neighbors plus my refrigerator chilled... a simple PVC end cap with an access hole drilled allowed me to use fuel from their fuel tanks with a drop tube that was adjustable for length... a small hole in the side near the top of the end cap allowed venting  .... which worked even in the light rain... the fuel tanks were elevated on a small near stand

@Beowulf
I thought about using the twelve gallon tanks so I would have plenty of fuel for long run times if needed.
Due to cancer I've been given a weight limit of 30# so I have to have somebody lift them for me any way.
The tanks would be set off to the side so if they did leak it wouldn't be directly onto the generator.
I was a mechanic for 36 years and am very aware of how dangerous gas can be,saw a few cars catch fire
because somebody didn't tighten a fuel line enough.Thanks for idea of the disconnect I'll have to check
them out and see if they can be adapted to the tanks.

Doesn't have to be too high, only an inch or two above the inlet for the carb.

Don't forget to look at any heat shielding that might be necessary. You may also consider plumbing the exhaust out the roof using flexible hose.

Planned on running the exhaust out through the wall,less chance of water leaks.