Engine life and jets

[John Pennella]

I was just wondering if doing fatter jets and putting a high performance exhaust on a quad, specifically a 400ex, lowers the life on the motor. I think a pipe is good for letting the motor breathe and get that heat out of the top end faster, but if they hurt the valves while doing this. Im asking this because I go to lots of different places in Mass and they re all at different heights from sea level and if i jet the bike i dont want to have to change them to let it run good at different places and have the bike suffer with too lean or fat jets. Thanks for any help.

[400eXr1d3rZ]

As long as you rejet, you won't have any problems. I would get a slip-on instead of a full system, full pipes don't benefit on stock motors. The stock pipe isn't very restrictive (so i've heard) anyway. I'd look at HMF, Yoshimura, LRD, Pro Curcuit etc...

If you get a slip-on I would change the main jet to 155 main, 42 pilot, 2.5 turns out fuel screw. That should put you on the right track.

[John Pennella]

Ya see that kinda scares me with the whole main and pilot jet change cus my ride right now is unbelievably reliable because I left it alone and just put fuel activator in it which works awesome, and I would just hate to have to keep tuning the bike to different places unless if the set up u said is good and not too fat ur anything. Its just a real tuff desision u no. but i could always go bak to stok. glad i just thought of that lol. Thanks for reply too. sorry for the ear full.