That's kinda thick. You would be ok with 10w30, that is stock spec.
Carb cleaning 101? Buy a can or two of spray carb cleaner. Remove the seat so you can see better. Close the petcock and remove the fuel line from the carb. loosen the two clamps, front and rear carb boots. Pull carb out as far as you can. Unscrew the tors box/carb cap and pull out the slidew/ needle. Pay attention to how it comes out, it only goes in one way. Remove the float bowl screws and float bowl. Remove plastic baffle, main jet (brass thing) and pilot jet (inside tube next to main jet). Remove float and needle carefully. Pay attention to how it goes back together. Spray everything with carb cleaner. Spray through all passages and make sure it comes out somewhere to be sure it is clear. Oh, yeah remove the air screw and spray through there too. Reassemble.
It's a good idea to check the float level, but don't adjust it unless you really need to.