Its a stock 400ex. I have a UNI filter that will be put on after the exhaust mod is done. I'm looking at a full exhaust system. I want quality and so far I'm looking towards the FMF powerbomb and the FMF Powercore muffler. I hear the powercore is loud but a lot of riding is done on the ice on the lake here and up north on the trails. Stock motor with this exhaust and UNI filter what ball park range jet should work? I'm less than 2000 feet above sea level. I hear its cheaper buying jets single and playing with those. Any info, tips or opinions is appreciated, the more replies the better. Thanks

 

probably best to go up one or two sizes on the jet. Try them out for a good ride and then see what your plug looks like. You might try calling the manufacturer of whatever pipe you buy to see what they recommend, and many times parts dealers will include the jets with full system packages...even if you don't buy the whole setup, just asking them will usually get your answer

As far as your exhaust goes...and all of us here are about performance...it's one of the fun things about ATVs...but for the sake of the future of this wonderful sport, do not contribute to the already prevailing bad attitude of the public towards off-roaders by getting a loud exhaust.

Louder exhausts do not make an appreciable difference in the performance of your ATV over quieter exhausts, but they DO create an appreciable difference in whether your neighbor thinks you are an insensitive dolt making a lot of unneeded racket on your obnoxiously loud ATV, or thinks you are just some outdoorsman out enjoying a ride.

 

I put the FMF Power-core 4 on my 01 Honda 400ex. Its a great pipe. You really don't tell the difference until you start hitting jumps and need the lower end power, then its night and day. It actually isn't that loud, unless you take the spark arrestor out. Then its very loud. I looked into the header for mine, and ordered it. I just got a call today saying its unavailable anymore. Thoughts????

 

the white bros. e series pipes for the exs are nice

 

thats true, the full white bros e series has one of the best flowing headers availible. and there not that loud, my friend has one. he used to have a power bomb, then he blew it up and got a 426. then during a race he wrecked and broke the pipe, and found a white bros on ebay and is more happy with it than the fmf, he said more top end. i will admit it sounds better too.

 

if your not gonna do any big mods, a slip on would be perfectly fine. the stock pipe is decent, plus price vs performance isnt really worth it to me. the popular full systems are like 450 and up. you can grab a slip on for round 200 and spend the other 250 on something else. maybe nerfs, a cam, better tires etc. also the powercore is LOUD. have the full system on a 300ex and its uncalled-for loud. gotta quiet core to install so well see after that.
I got a Lexx slip-on, on my 400ex and it sounds great and is built nicely.