Originally Posted by jepho
Does the two stroke engine run on a petrol and oil mixture which is bought ready mixed?
You don't buy it ready mixed. You may see people referring to "pre-mix" That means the oil is added to the fuel tank before going out. Usually at a ration of 50:1 (1litre of oil added to every 50litres of fuel). You can't buy it premixed. Don't think you can buy motorbike 2 stroke premixed anymore - but even if you can the oil is different. Motorbike engines are air cooled and so run hotter than a boat engine which is water cooled. The oils are different (you need an oil that is classed for TC3W).
A litre of TC3W costs about £10, but if you buy 5litres you can reduce the cost to ~£5/litre. You stick 30litres in a red plastic fuel can and then add 600ml of TC3W... Give it a shake to mix - job done.
More modern 2 strokes don't use pre-mixed fuel. So your fuel tank is 'pure' petrol and there is a reservoir on the engine for the TC3W. The engine adds the right amount of oil, either at a fixed rate or some engine management process.
What you need to know about 2 stroke vs 4 stroke:
2 stroke engines are lighter - so you can sometime put more power on the transom because the engine weighs less
(most) 2 stroke engines are simpler (they still break but usually are simpler to fix
2 stroke engines are noisier (if you are underway that *may* be less of an issue. if you are at tick-over or trying to coach/train people it becomes a challenge.
2 stroke engines are smellier
2 stroke engines tend to leave a bit of an oil slick around them at tick over
2 stroke engines can lie of their sides - probably not relevant here but if you have an aux engine etc thats not on a bracket it needs to be 2S or you get a headache.
2 stroke is less fuel efficient
There is a modern variant on 2 stroke that people either love or hate. It uses fancy modern engine management stuff to manage oil use etc... the general rules don't all apply.
There is a lot of marmite in TC3W ;-)