Been thinking on doing some modifications to this atv and I wonder where is a good place to start as I do not have all the money to do it at once so I need to do it in a order.. so a pipe and rejet kit to start? Then possibly a new cdi box and coil? Then a big bore 330 kit? What would be the best route to take?

How hard is it to double this engine power from 20 to 40 hp?

Thanks

 

you are right on track with the exhaust, the stock head pipe is very small,aftermarket headpipe and muffler makes a lot of difference. Be sure to put heat blocking reflective tape under fender where pipe runs under your right leg, or it will melt a hole in the plastic. Seen a lot of piped 300exs with a burnt spot or hole there, put tape on my sons 300ex when we piped it,no problem in years. Next free mod is drilling holes in the stock air box lid,it only takes in air through 2 frame tubes, so that chokes it off. Then you can bump up the pilot jet one size, and go up 1 or 2 on the main jet to get you close. The only problem you will have is the pitiful rev limit on the stock cdi, when you open up the intake and exhaust,it revs so much nicer, you are constantly hitting the limit,making you short shift,and you cant hold it wide open on top or it will miss and sputter. Put in a +1000 rpm cdi, and you are set,or you can regear with a bigger front sprocket to keep the rpms down a little. After that,then you are looking at engine mods for any real hp gains, doubling hp is going to take a bit of cash,better off putting a good suspension under it so you can drive it faster safely.
a pair of 400ex a arms and shocks up front with a top mount adaptor for the shocks will make it ride and handle much better,and spacers in the back will help cornering a lot.