excerpt from: http://www.radford.edu/~wkovarik/lead/overview.html



"When you fill your car up at the gas pump, you may notice that you are
using "unleaded" gasoline.

Lead is not something that comes with gasoline that has to be taken out --
it was deliberately added by the oil industry to boost "octane" or
anti-knock ratings for fuel. It had to be phased out by government order,
for public health reasons, starting in 1975, and concluding in 1986. It was
also banned in various European nations in the 1990s. It is still having
serious public health impacts in developing nations, and a complete global
phase-out has long been advocated by the World Health Organization and all
other international health organizations."



excerpt from: http://www.chevron.com/prodserv/fuel...etin/unld-gas/



Marine Engines:

There is concern about older four-stroke cycle engines in marine service,
which were designed prior to the introduction of unleaded gasoline
(pre-1974). Under severe duty, these older engines could have valve
recession problems. If these engines are in severe duty service, owners
should consider installing hard seat inserts or using lead substitute
additives to minimize valve recession. Products like this have been found
effective in minimizing valve recession.

Mercury, who is a major supplier of Stern Drive Engines for marine use,
advises that their engines are automotive based and have hardened exhaust
valve seats. Most of Mercury's outboard engines were developed with unleaded
gasolines, and Mercury's only concern is with octane number.

All of Outboard Marine Corporation's current four-stroke cycle engines were
designed for unleaded gasoline and valve protection additives are not
needed. Additives are also not needed for their two-stroke cycle engines,
however, some of them may have the need for octanes higher than 87(R+M)/2.

The newer Volvo Pinta Stern-Drive four-stroke cycle engines are designed for
use with unleaded gasoline. Some of the older engines are not. We would
suggest owners contact their dealer for advice if they have an older engine
in severe service.

Yamaha outboard engines operate satisfactorily on unleaded gasoline. At
least one model, a high performance Model 225, requires a minimum 89(R+M)/2
gasoline.

Outboard Marine Corporation has issued a Service Letter for General
Information #53, August 1985, subject: Gasoline Lead and Alcohol. This
bulletin is very comprehensive on their position regarding unleaded gasoline
use and has extensive guidelines relating to their minimum octane level
desired. This should be available from Johnson and Evinrude dealers.