Does changing the size of the main jet make any difference in power? Which size would be the best for woods riding where I need lowend?

 

Change jets only if needed if you bike is stock then you might be able to go down 1-2 jet sizes on the main jet, But you will need to do a plug check to make sure you are ok and not too lean. You might notice a small gain in performance but nothing huge.

 

with stock carb and pipe,there anymore thing to check beside,i guess the stock main jet is 240,
in the middle of summer like that when temp is pretty hot,you can go down 1 or 2,i would put a k&n air filter
in that thing then starting to drop the main,cauze you won't see any power gains,but i do see you have already the wiseco in it,give it some more air and you'll notice maybe a few mph.