Ok so i have finally broken in my new 400ex and done the first oil change. I am now going to spend some money and buy some performance parts for it.I have had a hard time deciding what exhaust to get. I only need the exhaust for trail riding. I am going to just get the slip on. I have narrowed it down to a few choices. The HMF sport seris slip on, FMF powercore, or the FMF Q4. I just dont know which one is better. As for the air filter i think i am going to just get a UNI foam air filter. Because i have heard a lot of bad about K&N. The only thing that i have left is the jet. I have know idea on what size jet i should use. I am slightly above sea level. Any thing that you have to say can help. Thanks

 

SAme here but an 02, I suspect this subject has been discussed a time or two before. Is there different jet to be used in summer and winter riding?

 

HMF makes a good exhaust, I have the Utility series on my Vinson, but I run a "quiet core" insert as well, as it is too loud without it...you may want to consider getting a quiet core as well.

K&N is a good filter, but it is more racing oriented and requires a LOT more regular maintenance. I use a UNI on all my quads.

You can get the correct jet by:

1. Calling the pipe manufacturer to see what they recommend.
2. Calling the part seller...many times they include a larger jet with an exhaust system.
3. Talk to the parts guys at the dealership. If they don't have the answer for you, start taking your business elsewhere as they are obviously incompetent.
4. Roll the dice and buy the next two sizes larger main jets. Install the smaller one first and see how it runs. If it seems to run hot, then go with the next larger size jet. This way is a lot more work and should only be done if you strike out completely with the first 3 suggestions

 

Fmf powercore is what i have and love it buy the fmf power up jet kit it has everything

 

The UNI air filter for this has a plastic cage, that will eventually warp under the stress of the tight band. Get the ProDesign (ProFlow) unit instead (comes with a filter made by UNI filter). It has an aluminum adapter that goes into the boot, and will prevent it ever collapsing!!!

 

On the jet kit you can call dyna jet and they will help you out on what you will need.
Dynojet Jet Kits - Offering Motorcycle Jet Kits & ATV Jet Kits Hear is the link to there web sigh.