Here are the Big 3 taken from Jesters post in the mod section
The header pipe on the raptor 350s are good, and I personally, among many others would not change it unless you want to spend the extra money. If you do the following brands of headers are commonly used.
-FMF Power Bomb Header
-Pro Circuit Header
A lot of 350 owners ride with the HMF slip on. Its a highly recommend slip on with a lot of gains. Other well known brands are.
The air filter goes great with a pipe upgrade. You will feel the power increase of a filter more with the add on of a exhaust. Depending on weather you want to go foam or paper or high flow or replacement is up to you. Modquad makes a great High Flow setup for around 100$ in foam and paper.
-Modquad System with Foam Filter
-Modquad System with K&N Filter
LID OR NO LID?
Well personally, I run with no air box lid. With the way the seat sits so close to the air box, it makes for a very good surrounding barrier to keep mud and dirt out of the air box. If your not into completely removing your air box, there is something called the "Pro-Tec Airbox Lid."
**Do not take your air box lid off if you only have a air filter that is a direct replacment of stock. Only take your air box lid off if you have a pro-flow kit which allows you to take the lid of because it doesn't use the lid to holed the filter in place. With Yamaha's design, the air box lid holds down the air filter. With removal of the lid the air filter will come loose and just sit in your air box, doing nothing.**
**By doing any of the above mods, you will be changing the amount of air that goes into your 350, thus requiring you to rejet your carburetor. When adding a pipe,filter and running with no lid most people use the following jets;
125 pilot jet.
155 main jet.
Clip in middle position (stock).
This do vary from place to place because of climate and other factors but the above jet sizes are starting points..**
With the whole filter kit with adapter you have the new adapter you clamp the filter on to. Without the adapter the filter just sits in the air box and you have to have the lid on to hold the filter in place. Hope this helps.
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