Pollution has also played a dominant role recently
for the reduced popularity of small two stroke engines
with crankcase scavenging. This two stroke
engine mixes fuel and engine oil for lubrication and
this further adds to the already higher emissions than
a four stroke engine. The main source of pollution
from two stroke engines with crank case scavenging
comes from the lubrication oil, because with this
simple design they do not have a dedicated lubricating
system and the oil burned in the combustion
chamber causes exhaust pollution.