I see this often regarding 2T bikes. I wonder how 2T outboards react to different ratios? My Yamanha says 100:1, my Mariner 30 says 50:1.
Will they produce more power at say 30:1?
The Mariner is 26.3 cu in (430cc) and wot at like 5000 rpm.
(?)
The Mariner run "dry" and quite well with 90:1 Amsoil, good throttle response, fells snappy, as said. But maybe it will have more pull with more oil?
Originally Posted By: mlatour
Originally Posted By: used_0il
I notice on 2-stroke dirt bikes that use pre-mixed gasoline, a line of
engine oil dripping from the exhaust pipe.
With better oil, the line becomes thicker and the blue smoke less.
Also with better 2-stroke engine oils, it seems that I could use
28:1 instead of 40:1 without an increase in blue smoke, but the line
of oil from the exhaust pipe increases.
I'm guessing that somehow the oil is separated from the gasoline
during operation. The higher the RPM, the better.
Would this indicate that high RPM 2-stroke engines can
tolerate a higher oil ratio than low RPM 2-stroke engines?
In the 2-stroke dirtbike world, excess unburnt oil leaking from the silencer or exhaust flange area is commonly known as 'spooge'.
You never ever cure this by changing the premix ratio, you have to re-jet the carburation for the ambiant conditions: temperature, elevation and humidity.
The choice of oil also affects this, 'racing' type oils with very high flash points used in non-racing condition never get hot enough to completely burn properly.
A 'perfect' carburation setting on a dirtbike can tolerate at most a 10°F to 15°F temperature swing before it requires re-adjustement to keep it in tune meaning
a change in one or more of the carburator's metering circuits: air screw, pilot jet, needle, needle clip position, main jet.
Mix ratios,
it's been dyno tested that more oil makes more power (at the expense of throttle response) due to better piston ring sealing.
High-revving 125cc and smaller (12500rpms) motocross engines run in the 28:1 to 32:1 range,
while lower revving 250cc and larger or, enduro / off-road type bikes can safely run in the 40:1 to 60:1 range.
On my YZ125 dirtbike, it can mean starting off the day in cooler weather and having to
re-jet the carburator by lunchtime to keep it in ideal tune, due to temperature rising.