2/3/00
Nearly everyday we get a mower or trimmer or other small engine powered unit, with carb problems come in the shop due to old fuel. It ain't gasoline any more and it needs to be treated for what it is. Designer Motor Fuel. As with any other "Designer" anything, it tends to be short lived.
Todays fuel is formulated for todays automobiles with all sorts of computer controlled, emission reduction devices. One of it's properties is to vaporize quickly which allows an engine to use less fuel more effectively. This rapid vaporization also reduces it's longevity to a useful old age of 30 days. Yes it will operate an engine beyond that but what it starts to leave behind as a result is a sticky varnish that adheres to valves and valve stems, pistons and rings. Eventually it will cause hot spots and damage.
Often, an intake valve recieving this pasteing of goo will freeze up after the engine has been shut off and cooled. The complaint, "it ran fine yesterday and I just can't understand why they build these engines so poorly". Language deleted here. Well friends it isn't the engines fault that you glued the valve shut by using old fuel.
This sort of damage ocurrs from use of slightly old fuel and happens when the fuel hits hot parts of the engine.
When fuel gets a bit older, depending on it's original quality and just how old it really is, it was at the filling station for some time after all, it starts doing things to your carb and fuel system. The same sticky goo is a result and it's simply from chemical aging. Jets and fuel passages are blocked, inlet needles and floats are stuck. Throttle valves can be froze up.
The results of using old fuel;
1. At the very least, a cold engine will be hard to start and keep started until it warms up. That should be your first warning.
2. Valve train damage requiring a valve job. Many mowers and all new ones now being built are OHV. They are more prone to this problem due to smaller components and lighter valve springs. An OHV engine valve job will cost you about 50% more than the older flat heads.
3. Carb shellacing, will be followed with a carb overhaul, perhaps carb replacement.
4. Irreparable internal engine damage.
Still wanna use old fuel? Fine with me, I repair 'em. You can come to my hometown of Vegas and spend all your money also, help our local economy. That's good for me too :-)
Try this. Buy your small engine fuel on the first of every month. Whatever is left at the end of the month, use it up by pouring it in your car. Uhh, make that, your cars fuel tank.
Happy Mowing, Bob............