Can someone explain old gas?

bell47

Cadet
Joined
Sep 6, 2008
Messages
14
I've got a post running about my 1988 yamaha 175 that has an idle problem. I'm beginning to think maybe it's just old gas. But here's my question. How old is too old? What are the symtoms of running old gas in a motor? I ran my boat today after cleaning the carbs and doing a link/sync by the book. It started well, warmed up(idled smooth), ran strong, made the rpm and speeds it should( after minimal tweeking) but after about 20 minutes of running and checking it wouldn't hardly idle again. I had put on a new filter/water seperator before running, and the screen on the side of the motor is spotless again. So, when fuel is old what happens to it? Will it gel up or shelac past the filter as it's going through the carbs? I honestly can't see how the fuel getting to the engine is not clean, but if it's the actual chemical breakdown of the fuel then I gotta drain it. Anymore suggestion? Anyone know of a cheap electric fuel pump to pump out a tank?
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Can someone explain old gas?

Maybe you did your link/sync and initial idle adjustment while motor was cooler than normal running temperature, and after you ran it up to regular normal running temperature maybe you need to tweak that idle screw a bit to bring it up around 750 RPM's. How old is your gas? I believe gas can degrade in a fuel tank in a matter of weeks, and certainly after several months, but any different fuel could take longer or shorter. I mean if you bought gas at some out-of-the-way, low volume gas station, it could have been laying in their tank for quite a while. I use Stabil all the time, less when I'm running the motor every day and more during extended lay-ups. I also drain my carbs for extended lay-ups, and it's fairly easy to do and good insurance against carb float bowl deposits. Good Luck!:)
 

bell47

Cadet
Joined
Sep 6, 2008
Messages
14
Re: Can someone explain old gas?

I keep hearing that gas degrades or starts going bad after several weeks or months. If the engine was run out of gas and the carbs drained, how would clean, but old, gas coming from the tank affect how the engine runs? Gas wasn't left in the carbs. When I said above that it just wouldn't idle after 20 minutes, I miss communicated the problem. It started to idle rough after about twenty minutes of hard running, starting, stopping, ect... the more I ran it the worse it idled. Now, after about an hour of running, it dies at idle like in the post before. Top end performance never changed. Also, when I say OLD gas, it does not have that old rotten gas smell, it is just a couple of months old, but I keep hearing this is pretty old. Should I drain it, flush the tank, start with fresh gas with stabil in it or ???? we're talking about 75 gallons of gas in the thing. Thanks for the advice guys.
 

newbie4life

Chief Petty Officer
Joined
Jul 19, 2007
Messages
410
Re: Can someone explain old gas?

I feel your pain, buddy. My mechanic brother in law says "Remember, gas starts breaking down after 30 days." To which I reply, "Good deal... Bring me all your old gas and I'll stick it in my 1945 Farmall H."

Get this -- this tractor sat for 4 YEARS. No Stabil, no draining the tank, carb, etc... charged the battery, and hit the starter button. Turned over half a dozen times, and fired right up. Crazy.

Yet, my boats that I've had over the years needs to be drained to ensure smooth operation. If not, I will most likely end up having the carbs cleaned out, and dink around with it to get the engine to run properly again.

My thought for keeping the boat clean is this - if the tractor dies, I'll use another tractor to get it home. If the boat dies... it's much less handy to get a tow. :)
 

kmarine

Chief Petty Officer
Joined
Nov 5, 2010
Messages
591
Re: Can someone explain old gas?

I would suggest taking a fuel sample. Pour into clear container look for bubbles in the bottom, like water droplets. what color is the gas. I work on some boats that have sat with old gas for 5 years wothout major problembs and a weel later have a boat come in with a fuel problem that has been used 10 times previously that year. I sometimes use seafoam or lucas fuel conditioner, I have good luck with them. I also have a fuel seporator filter with a water drain valve on the bottom for water removal. I dispose of bad fuel after removing it from old boats by mixing it with new fuel 5 parts new to 1 part old. I then use it in my tow vheicle which gobbles about 50 gallons a week.
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,678
Re: Can someone explain old gas?

Two stroke motors are high precision beings and hate bad gas. If you want to keep your fuel fresh use Stabil Marine religiously. It will also help to avoid damage from the alcohol in the fuel. We are all experiencing water in the fuel and this is also a result of alcohol in the fuel. A water trap filter on your motor is a must. You will need a big one. All this alcohol ***#@ is thanks to our smart government of course.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: Can someone explain old gas?

Fuel does NOT go bad in a couple of weeks and it is still perfectly fine after six months. Our boats up here in the tundra are layed up for six months every winter, as are our collector cars, lawn mowers, tractors, and yard equipment. They all run fine in the spring. Use a fuel system treatment and go boating.
 

Bamaman1

Lieutenant Commander
Joined
May 15, 2011
Messages
1,895
Re: Can someone explain old gas?

One problem is that Stabil actually has a shorter lifespan than the 90/10 gasoline. Another is that as gas degrades, an acid is produced that affects rubber parts in your fuel system. This can include gas lines unless they're special gas line tubing. Needle valves in carb. bowls also have rubber on the "points", and stumbling engines are often caused by sticky needle valves.

I run a pontoon boat, and I have a 6 gallon steel and a 12 gallon plastic tanks. (I have no use big permanent mounted fuel tanks.) I run the fuel out of my motor while winterizing the engine. Then, I'll empty remaining gasoline into my automobiles. I'll start the Spring with fresh fuel. Locate a gas station selling 100% gasoline--even if the fuel is more expensive.

Good luck to you with your rough running problem. Hopefully it's just a minor issue.
 
Joined
Oct 28, 2010
Messages
923
Re: Can someone explain old gas?

Fuel does NOT go bad in a couple of weeks and it is still perfectly fine after six months. Our boats up here in the tundra are layed up for six months every winter, as are our collector cars, lawn mowers, tractors, and yard equipment. They all run fine in the spring. Use a fuel system treatment and go boating.

Uh...no
degrading_gas.png


fuel_decay.png
 

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Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: Can someone explain old gas?

How long has OMC been gone? And even Mercury has backtracked on their findings and recommendations about ethanol blended fuel. If you want to be critical about fue shelf life, any fuel, diesel, regular gas and ethanol blended fuel ALL begin to degrade the minute they leave the refinery and they are all subject to water issues. If you are old enough to remember the Yellow bottles of gas line antifreeze, and lived in the northern tier of states, you got used to using this stuff during the winter. Why? Because water in the fuel froze your gas line. When was the last time you saw a vehicle with a frozen gas line that has ethanol fuel in it? It doesn't happen. This topic has been discussed to death, older literature is not accurate, and it is simply not worth discussing any longer. We have used ethanol blended fuel here since 1997. It is simply not a problem. If you happen to own an older engine that doesn't have ethanol tolerant components, it is about time they were changed them as the fuel system is likely gunked up from lack of maintenance anyway. Adapt or suffer the consequences. You don't have to buy a new motor to adapt.
 
Joined
Oct 28, 2010
Messages
923
Re: Can someone explain old gas?

I know that ethanol is not the problem, that is not the argument. The argument is the shelf life of gas. This is from BRP 2006-06, I don't know how much clearer I can make it for you...

brp_fuel_requirements.png
 

giericd

Petty Officer 2nd Class
Joined
Oct 1, 2011
Messages
102
Re: Can someone explain old gas?

it cracks me up, out of all that could go wrong with an engine to cause poor performance such as carb adjustments, linkage adjustments, CDI issues, stator issues, bad plugs, wrong gap of plugs, voltage issues the combination is endless but fuel issues are some of the easiest to trouble shoot. If you suspect it to be a fuel issue do a white bucket test, pour about 1 gal of suspected fuel in to a clean white bucket. Any water in the fuel will sink to the bottom and look like a bead, you will be able to tell if there is water in the fuel! If the fuel does not have water and is clean and clear it is most likely good gas. if it is cloudy there is a lot of free water in the fuel and you dont want to use that fuel. if it is off color like an orange tint then there is microbial contamination and you dont want to use that fuel. And one of the quickest ways to tell is get a removable tank with fresh fuel and run the motor, if it works fine with the removable tank and fresh fuel but runs like crap with the built in tank and old gas, well there you go! assuming your anti syphen valve is working correctly.
 

bell47

Cadet
Joined
Sep 6, 2008
Messages
14
Re: Can someone explain old gas?

That was done about the first day I started having these issues. The gas looks and smells like normal gas, but I keep being told how it goes bad so quickly I thought I'd ask. Thanks.
 
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