Post by Peter ZCan anyone explain if the recommend mixture set on
the bike applies to any oil we have today, or to the oil the manufacturer was
using back in 1984?
2-stroke oil may or may not be "better" today than it was
in the last century...
Some of the smaller oil suppliers just buy oil from some major refinery in
55-gallon drums and don't actually do anything with the oil they sell except
repackage it in their own container and sell it for a high price.
Generally, oils have been formulated for increasingly harsh service. That's why
you see all the different SE, SF, SG, SH, SJ, etc. ratings on the cans of
*automotive* oils. You might want to read the ratings (if any) on containers of
oil found on the shelves of your local motorcycle emporium and do a web search
for whatever manufacturer's oil interests you.
Selecting a 2-stroke oil and pre-mixing it is sort of like buying insurance.
You don't need the extra protection of an oil-rich mixture until you need it,
and then you really will regret not having enough oil when you have to replace
seized pistons or scored cylinders because you enjoyed the extra power of an
oil-lean mixture for a few miles at high RPM.
Post by Peter ZNever really did understand the whole mixing and ratio thing.
2-stroke oil pre-mixing depends on three things, the *size* of the engine, and
the type of oil, synthetic or petroleum based, and whether the engine is
air-cooled or
water-cooled.
A water-cooled engine will require less oil because it runs at a more stable
temperature. It won't burn oil like an air-cooled engine, so it will throw
excess oil into the exhaust port and upper exhaust pipe where it will turn to
goo, or even harden, blocking the pipe with carbon.
If you have a small bore 125 cc engine that runs at high RPM, you're better off
with a synthetic oil running about 40 to 1 ratio for two reasons. It has less
cylinder wall area that needs to be coated with oil and the small needle
bearings in the rods won't skid on the rod journal when you start the engine
up. Skidding needle bearings wear flat rapidly.
But, if I was riding a 250 cc or larger machine, I'd run petroleum oil at 20:1
or thereabouts, especially if it was air-cooled.
I found that my dirtbikes felt like they had more compression and were
"torquier" with petroleum oil at 20:1 mix. It was probably because the extra
oil sealed the piston rings better. When I experimented with synthetic oils,
the engine would idle at higher RPM and rev freely, but the type of riding that
I was doing didn't require high RPM work.
And, if you're experimenting with 2-stroke oils, be aware that some of the oils
will do strange things when mixed together. Like, one synthetic oil turned a
castor blend that I had been using into a hard varnish-like material when it
slopped over onto my gas tank and I actually had to chip it off...
And, like I said to another poster on this NG, castor oil pre-mix may smell
racy, but you need to tear down a castor-burning two stroke after every race
and clean the goo out of the rings or it won't run right...