Right now I have a completely stock 99 400ex. I was thinking of adding a k&n air filter and drilling holes in the air box lid. If I did this would I need to re-jet?
I would probably put in a 14-tooth sprocket too. Are there any other mods I can do to make my 400 perform better? I want a e-series but where I ride I can't have it much louder then stock, and I have heard that any after-market exhaust is a lot louder then stock. PLEASE HELP!
Thanks
Dave

 

Yes, you would have to rejet if you did those mods, and any aftermarket exhaust is going to be much louder than stock. If I were you I would get the K&N filter, jet it, and then do you airbox mods and see how you like the power increase. The next step would be getting into your motor!

 

I was just told that the e-series with the quiet core puts out 90db and stock is 88db. Is this true? If so I think I could get it. What kind of relativly inexpensive mods (under $200) could I do to my motor?
Thanks Dave

 

Alot of guys have gone to a JE 416cc 10.5 to 1 compression. If you can find the piston for like $150 you could probably get it bored and the gaskets for around $200. Assuming you can do the work yourself you could have a pretty sweet setup for around $200.

Pipes on a 400EX are probably not the best mod to do first. They are obviously easy, but they dont deliver the best bang for the buck. To be honest at the Birch Creek Nationals there were several 400EXs with stock headpipes and they were very fast machines.

Adam Smith

99 400EX