ORIGINAL: earlwb
Some of the noxious additives in pump gasoline are as shown here. The blends change with the seasons too. These substances tend to evaporate at different rates thus leading to a short shelf life for the fuel. Even if it is in a decent sealed container too. But in the engine carb it tends to evaporate and leave behind a varnish like sludge that gums up the carb.
Contains Benzene, CAS # 71-43-2. Contains Toluene, CAS #
108-88-3. Contains Ethylbenzene, CAS # 100-41-4. Contains
n-Hexane, CAS # 110-54-3. Contains Xylene (Mixed Isomers),
CAS # 1330-20-7. Contains Naphthalene, CAS # 91-20-3.
Contains Cyclo-hexane, CAS# 110-82-7.
Contains Tri-methyl-benzene (all isomers), CAS# 25551-13-7.
Dyes and marker
someone else uses this
Gasoline 86290-81-5 100 %volume
Benzene 71-43-2 0.1 - 4.9 %volume
Ethyl benzene 100-41-4 0.1 - 3 %volume
Naphthalene 91-20-3 0.1 - 2 %volume
Ethanol 64-17-5 0 - 10 %volume
Methyl tert-butyl ether (MTBE) 1634-04-4 0 - 15 %volume
Tertiary amyl methyl ether (TAME) 994-05-8 0 - 17 %volume
Ethyl tert-butyl ether (ETBE) 637-92-3 0 - 18 %volume
Sometimes they throw in some butane or propane too.
save for the last few ethers the rest are not "additives" but rather blending components and in some cases constituents of what is collectlively known as naphtha. Depending on where its cut they could part of either light or heavy naptha.
Butane and propane are added depending on the spread of other hydrocarbons and the volatility needed for the market and season. In winter, more butane or propane is needed to ensure the cars engine can start. Using a heavy, non volatile fuel will leave most vehicles standing by the saide of the road.
In terms of volatility, and the nature of how carburetors work, its seldom a good idea to leave fuel in a 2 stroke for very long periods so I'm not sure where the actual problem lies other than user behaviour. Direct injection and multi point injection engines work off very high pressure pumps so the volatility is not as big an issue for those engines as it is for a carburetored engine.
Cutting a long stroy short, truckracer nailed it in his closing line. gasoline blending is a complex issue that the end user has little control over because they don't participate in the forums that drives specifications or addresses marker related problems. What is certain is that the fuel you buy at a reputable service station under the banner of a recognised brands will conform to your local specifications and that is in itself a stamp of quality.
Wishing Ethanol away is not going to happen and eventually its going to be in the avgas too as Brasil is showing the world what can be achieved with E25 and E85. For now its a flavour that has to be lived with