Lemme toss in a few grenades here.....
It is always best to follow the manu recommended mix. I have had older stuff that ran 16:1!!!
The recommended mix is based on the bearing type of the motor, the cooling eficiency of whatever it has, and the speed of operation. Small tiny engines have no torque therefore must run at ridiculous speeds to make any power.
Use a 2 cycle oil that meets the latest TCW rating. Yes, it is a rating primarily made up for boats, but it is the ONLY rating, ie., there was never a quality/grading system in place for other 2cy utility motors so they adopted it. But dont kid yourself about marine motors, they make power in the 6000-6500rpm ranges, not 4000 and since 1) metal to water heat transfer is far more efficient than metal to air and 2) boats at times have a few million acre feet of water below them then the choice to liquid cool was simple. Stick your hand under the relief stream - thats hot water coming out. That 1.5L outboard is making over 200hp, thats a lot of heat.
And keep this in mind, 2 cy oil does not burn. Let me repeat, 2 cy oil does not burn.
did we get that? 2 cy oil does not burn. It does however partially oxidize and what comes out is black gooey 'carbon' that clogs your transfer ports and fouls the plugs. The latest 2cy TCW specs are designed to stay liquid or vaporous longer to exit the motor completely and what compounds do come out, are supposed to more readily decompose in the environment.
If you are carboning up, then some or all of the following is true:
1) incorrect (heavy) mix (either by mixing gas, or bad injectors)
2) clogged air filter
3) too large a main jet or too open of a pilot jet setting at idle
4) prolonged low speed operation or lugging the motor
5) weak spark- you name the cause
2cy motors have a narrow powerband and are designed to last there all day long. as little as 20%rpm less than rated power would be considered lugging. At the proper high rpms the following is true:
1) max efficiency is acheived as the expansion chambers are fixed in size an in the case of utility motors are fixed atthe power peak.
2) extra heat at the the piston(s) rings will cuase further expansion, giving a tighter compression seal. This will not only make better power, it will also avoid over pressurizing the case with hot gasses instead of cool air
3) extra heat at the exhaust xfer port will keep the unburned oil as a vapor/gas longer, so it exits completely
4) at max efficiency, the max amount of cooling air is brought into the case for cooling.
I would recommend as a good baseline, 50:1 for liquid cooled engines, 40:1 for air cooled engines. older 16:1 or 20, 24:1 can be run at modern 32:1 and 32 could goto 40:1.
I dont buy into the 100:1 amsoil claims. Too many scored bearings and burned reeds have resulted.
Besides, the fuel burn rate is a constant, based on what you can get TCW3-4 at vs amsoil, the cost/usage ratio does NOT favor the amsoil.
