If I jetted my 300ex would I feel a difference??

 

yes, the stock jetting sucks.
even if you had no mods (pipe, air box holes, etc.) I would still re-jet.
you can get a k&n atv stage 1 jet kit for about $45. it gives instructions for jetting a stock motor. they claim a big increase in the ads, something like 7% or something. I dont know if its true, but it still would be better than stock.

 

How would you go about rejetting it if it ran perfect and you had no mods? You would screw it up.

 

I dont know, ask K&N.

what I've been told is that the factory jetting is set to be able to run at all altittudes, which I believe is where the problem is. K&N claims to be able to increse horsepower 5% by installing one of their jet kits. like I said, I dont know if K&N is just trying to sell you their product, but the people I've talked to on these forums, and people at the atv shops seem to all agree on this. I dont have any first hand experience jetting a stock bike, so maybe I'm wrong.

so, if you like the way your bike runs, leave it.