It seems the longer my boats gas sits the more performance goes down, atleast it seems that way or maybe its in my head, or maybe its just my old ass engine haha (1985)... 

Do you close your vent cap when your storing your boat? I'm thinking that maybe condensation or something like dust is getting in the vent on my tank so I'm gonna try closing it after fishing from now on and see if it makes a difference.

 

I've never had to vent one I've had. Are you sure it's the tank or could you have a gummy line, filter or carb? 

The engine runs fine, it just has alittle hiccup every now and again, and it kinda seems like it happens less when fresh fuel is in it.... That might just be in my head though, the carb should be fine, I soaked it not too long ago.

The fuel lines are less than a year old, probably more around 6 months old.

The fuel filter is old as crap, that could possibly be the problem too.

Are you treating your gas? Gas can go bad quick... I would imagine if you add seafoam to your tank at the reccomended dosage you will notice an improvement.

my tank auto vents out the fill cap on the side of the boat.

1 hour ago, Kevin22 said:

Are you treating your gas? Gas can go bad quick... I would imagine if you add seafoam to your tank at the reccomended dosage you will notice an improvement.

my tank auto vents out the fill cap on the side of the boat.

I use startron when I am not using ethanol free gasoline.

On May 5, 2016 at 8:45 PM, Catch and Grease said:

I use startron when I am not using ethanol free gasoline.

All gas goes bad, not just ethanol blended gas. Not sure about Startron but Seafoam and Stabil treat all types of gas. Ethanol free gas just starts losing octane after a couple of weeks and we all know about ethanol mixed gas. After a few months even ethanol free gas is so low in octane it will run very bad and possibly damage your outboard.

9 hours ago, Al Wolbach said:

All gas goes bad, not just ethanol blended gas. Not sure about Startron but Seafoam and Stabil treat all types of gas. Ethanol free gas just starts losing octane after a couple of weeks and we all know about ethanol mixed gas. After a few months even ethanol free gas is so low in octane it will run very bad and possibly damage your outboard.

Yeah I started looking into that, I didn't know that gasoline went bad honestly... 

How long is it usually good for before it starts to go downhill?

 

Edit: Sorry, missed that you mentioned how long it last.

If you close the vent water condensation forms inside the tank, not a good.

85' OB is probably gas-oil mix and can be a problem with a fuel stabilizer not designed for mixed gasoline. Stabil makes a product for your engine.

I have always used the highest octane gasoline availble, nothing under 90.

Tom

Fill your tank all the way up with ethanol free gas before storage and you will be fine.  The less head space in the tank, the less the tank breathes each day as the temps fluctuate, thus the less moisture laden air that gets in the tank.  Stored mine for years this way never had an issue.  However my boat is really only not used less than three months :  part of December, January, and February.

The old discussion of leaving tanks full or empty for long storage comes to mind.  I live in Michigan.  Boat in garage.  Sometimes sees 22F during winter.  I change oil, fill engine with propylene glycol, fog cylinders, and leave gas tank almost full with Stabil and leave vent open on gas tank with fuel line disconnected.  Starts right up in spring.  No issues. 1991 2 stroke 4 cylinder oil inject Mercury. 

What do you mean when you say  "fill engine with propylene glycol"?  Just curious?  I have heard of inboard boat doing this in the engine block but Outboards are designed to self drain so I am wondering what you are filling.  Thanks

Outboard - filling cooling intake till i see pink come out discharge.  Theres always potential for residual water to sit in the engine.  

Always leave vents open while in storage, especially with drastic temp changes.  Best advice is to fill up with ethanol free gas and use Startron or one of the other products mentioned.  I once left the vent closed on an expensive metal gas can (not on a boat) and it crushed itself from the pressure with a temp change.  This was in a garage, so no direct sun or anything.  

Forgotten to say leave vent open.  Always.