There is no difference in 4 stroke and 2 stroke oil, except that 2 stroke uses non-detergent oil. 2 stroke oil is actually 30 weight non-detergent (30wt ND) oil. Oil with detergents will leave deposits in 2 stroke cylinders, and is not recommended.
4 stroke
40:1 is the mixture of gas to 2 stroke motor oil (only)
The motor oil to use in a 1982 Yamaha 250 XT 4-stroke dirt bike is a 10-30 or 10-40 weight oil. Castrol GTX Motor Oil that is of this weight is the best oil to use in off road bikes, because it is a cleaner oil. It will not gum up the works of smaller engines like regular motor oil.
buy garden engine oil from Halfords then follow your manual instructions for a mix
No
32:1
Soy
Your bike is a 2 stroke. since you are mixing gas and oil together oil naturally blows out your tail pipe. if this is happening, then there is nothing wrong with your bike, unless it is a 4 stroke.
If your 2 stroke dirt bike starts to smoke really bad that means you have to much oil in the fuel or the wrong kind of oil. Or the pistons, oil rings or cylinders are badly worn.
Best to use two stroke oil. Mix it with the petrol, (I guess you know this)
standard 2 stroke oil snowmobile or dirt bike oil
Depends on the manufacturer as to what type and weight oil to use.