I use Sta-Bil in every can of fuel I buy so I don't have to worry about adding it later. I just put the mower away without regard to the fuel level, including after the last use of the season - no need to do anything with the stabilizer in there. Since starting this practice years ago, I have had no fuel system trouble on my mowers. I have one that is a 2004 model and the other is a 2008. I thought I needed to clean the 'orifice bolt' on my 2004 LB 10684 with Tecumseh 195cc but it looked brand new and even the small hole was clear. It turned out to be a governor adjustment needed - after 13 years. :)

The Sta-Bil I'm using is the 'Marine' 360 for Ethanol Fuels.

When I'm getting ready to use a mower, I just check the fuel level and top off as needed. The fuel can is usually sealed and the mower tank is vented, so it makes more sense to me to not fill the mower tank until it needs gas. IOW, don't fill it up until you are going to use it, so less fuel is exposed to evaporation and possible moisture accumulation.

if your using pure (real) gas you shouldn't have any issue's either way.

(original poster). Thanks to both. I think I will start filling and leaving full for the week (if it makes no bad difference). I have the feeling I am having evaporation from the tank. (it will probably still happen but I won't notice it)

Interesting, same thing can happen with older cars and trucks, pre-emissions. A partially empty vented tank will act sort of like a bellows, expelling volatiles from the fuel during the day and drawing in humid air at night, which will then condense on the walls. After a season or two it can add up to a lot of water in the fuel, causing rust and sediment. A reasonably full tank of fuel helps prevent this.

It is amazing at how much water does get inside a typical 1/2 gallon mower fuel tank. I usually find some floating around in the bottom of the carb bowl if it has been awhile since I got into the fuel system, and I live in West Texas where the humidity is relatively low most of the year.

Many of us do not have the option of 'real' gas since its not sold in our areas. Of course there is the straight gas and 2-cycle mixes available in small amounts from the hardware store but there is no real reason to use it as long as you use a fuel treatment/stabilizer.

I always shut off the gas and let the carb run dry on all my equipment after using it. Just piece of mind and no worrying about a gas flooded crankcase or gas leaking on the ground (darn updraft carb)

yt, i agree, 5.00 part can save alot of headaches.

yea..hard to get real gas...just add the stabil and do whatever all summer...I always run it dry at the end of the season.....especially my 2 cycle stuff.

Just to be clear here, a fuel preservative won't do anything to prevent condensation buildup in a metal tank that isn't topped off.

I always run lawnmowers, snoblowers &c dry at the end of the season, though I have read recommendations by some small engine mechanics that this can cause certain seals or gaskets in modern engines to dry out. They actually recommend _not_ leaving them dry for long periods. Ethanol laced fuel does have the characteristic of absorbing small amounts of water, to be burned. But it doesn't store as well and wreaks havoc with rubber parts. One trick that works slick, at the end of the season, is run a tank of Coleman fuel. It is basically a low octane gasoline with no additives and does not gum or turn to varnish. Too expensive to run on a regular basis, it is perfect for infrequently used equipment like emergency generators or folks too lazy to drain the tank at the end of the season.

hi all, i know you already checked, but for those that haven't.

http://www.pure-gas.org/

One thing I've noticed on the 8hp Wisconsin in my Bolens is when running on 93 pure gas I have to turn the main jet needle in a half a turn (lean) for it to run normal or else it runs too rich and with 87 E10 put back in I have to turn the needle back out half a turn (rich) to get it to run right.

'I always shut off the gas and let the carb run dry on all my equipment after using it. Just piece of mind and no worrying about a gas flooded crankcase or gas leaking on the ground (darn updraft carb)'

Right - I managed to leave out that little detail (can be a big detail if your fuel runs out on the floor in your garage) :)

I meant, just park it and turn the fuel off. I still don't agree with draining the carb or running it dry IF you use a stabilizer.

I fill the metal tank on my snow blower. I dose all my OPE with MMO when I fill them. Plastic tanks are filled as needed, except for the Mantis which get emptied and run dry per the manual.