Modern Fuel Formulations

It is always such a pain to get the lawn mower running after it sits for the winter. The gas seems to age very quickly and the carburetor ports and jets get all plugged up with a jelly like film.

Without being a chemical engineer, I am guessing that modern fuel formulations make gasoline less stable. I am under the assumption that this fuel is hygroscopic meaning that is sucks up water. When a lawn mower or an old car with carburetors sit in a building that does not have a stable temperature, there is a lot of condensation on cold engine parts in warming air which gets into the fuel and the gas absorbs water from the air.

The reason I am mentioning this specifically with carburettor engines is because the fuel system is totally exposed to the atmosphere. Modern car have an evaporative emissions system and a non-vented fuel system. There is less chance for atmosphere to come in contact with gasoline. Gasoline is not only spoiled by water getting into it but the atmosphere breaks it down and evaporates it out leaving behind a residue that is sure to make a mess of all the small orifices inside a carburetor.

This photo is of a Weber IDA carburetor from a Porsche 911T. The amount of sludge in the float bowl was so thick that the float could not fully open. In trying to diagnose the problem with these carburetors, I kept pulling the idle jets and cleaning them only to make the car run worse! All of the ports were packed and the carburetors soaked for days to free up the sludge.