Which is the safest to use ????
If the base fuel was the same, which it usually is not, then the
leaded fuel is by far the worse due to the lead poison emitted.
However to achieve the octane rating in fuel without lead, extra
refining is done, and in some locations/refineries this means more
aromate (thought to cause cancer) are present, and so emitted as
unburnt HC.
If it were me I'd keep as far away from lead fuel as I could! If it
is a low performing 2 stroke, it will probably run well on a low
octane unleaded fuel which should contain less other 'nasties'.
Your conclusion is right, the rest of your post less so. Unleaded
petrol does not generally include more aromatics (in Germany often the
reverse is found) but does contain partly oxidized components. These
besides elevating the knock rating significantly improve burning and
lower HC emissions. Besides two stroke engines always have problems
with plug fouling anyway and thus are far more susceptible to lead
fouling problems than four strokes. Substandard ignition performance is
just about the biggest possible contributor to emissions, so I keep
lead even further away from two strokes than from engines in general.
Tschoe wa
Axel