Well, I'll tell ya... If anyone figures out a way to deal with this problem; TELL ME FIRST!!

I just went through a horrible experience with this. I had left fuel sit in my dual quad hot rod boat, and all but ruined 800 dollars worth of carburetors. I think I've got them cleaned now, finally, but what a nightmare!!! The deposits that were left behind after the fuel degraded and evaporated could not be dissolved even with acetone!!

As far as our airplane engines, the biggest problem is with the regulator diaphragm. Every time I talk about this, I get a slew of comments from people saying "Oh bullcrap, I have my fuel sit for a year and my engines fire right up and work perfectly." Well, I don't know about that, but I DO know that is NOT the case here in Tucson, Arizona. I fix hundreds of machines with fuel system malfunctions here, and fight the battle with my airplane engines too. It doesn't seem to matter whether you store them "wet" or "dry" here. Walbro has supposedly invented a better diaphragm, and they announced it in a "news flash", but I have since contacted them several times and no answer on the diaphragm issue. Don't know what's up with that....

There are several things you can do, shown here in no particular order.

1. Set your e-mail to send you an appointment notice every month that says; "CHANGE GAS IN TANK AND RUN ENGINE WITH FRESH FUEL!!"

2. You can use Avgas. It seems to evaporate away cleanly, though it will still leave the oil behind and that can cause its own problem with your felt clunk filter and carb filter. Also, the FAA has gotten tough on selling Avgas only when put directly in an airplane fuel tank. I can't even get the "out in the country" small airports to sell it to me now.

3. I use a mixture of Coleman Fuel mixed at 20:1 with dino oil and a touch of Sta-Bil as a storage fuel. Fill the tank nearly full, run the engine long enough to get the fuel in all the jets, then cap off the vent line and wrap the carb in plastic to prevent evaporation. I DO NOT AND WILL NOT FLY WITH THIS FUEL AND DO NOT RECOMMEND IT. (A bunch of people will jump in here and tell us that it is fine. The bottom line is the engine manufacturers never, ever recommend fuel below 87 octane, and Coleman fuel is around 50 octane more or less. So there you have it.)

4. You can use the special, non alcohol two stroke fuel sold in home improvement stores. This is expensive. Also, any time your fuel evaporates, you are going to have a mess in the carb and in the fuel filter clunk. So preventing evaporation is a good step with ANY fuel.

I use number 3 myself, though I admit number 1 is the best of all options. But getting 10 airplanes out of storage and servicing the fuel system each month would be a PITA!!

The bottom line is, if the engine has sat for very long, pop the two covers off the carb and check things out. On the pump side, the diaphragm should not be distended, and the filter screen should be clean. On the regulator side, the diaphragm must be floppy loose and flexible. If not, replace it. A partially stiff one will drive you nuts trying to tune the engine. Lastly, if all the fuel evaporated away, you should replace the felt filter clunk in your gas tank, and check that the fuel lines are still soft and pliable. If all this makes you think maybe you should change to fresh fuel and run the engine every month.... you would be correct!

AV8TOR