SAE 10w30 Full Synthetic any major brand.
It will probably just foul the plug or wreck the engine because the oil is not designed to mix with the fuel and will not lubricate the motor.
regular gas xr is a 4stroke engine
what type oil to use on 4stroke 2.5mercury outboard
engine oil
5W30 oil.
4 stoke engine oil
yes if it is 4stroke witch i think ttr 90 is! use good type of gas, you have separate place for engine oil, but with 2stroke engines you have to mix gas and oil together.
For stroke engine bikes use the engine oil as gear oil. In case of a two stroke engine you can use regular 80 W / 90 gear oil.
5w30
10w30
If you do not want to use Polaris trans oil ,they recommend 30 w engine oil