i have the t4 slip on, kn power kit, smaller front sprocket. I noticed the differance. Throttle response was way better and pulled stronger.My buddy who has a z400 drove it before the mods and then drove it just tonight. He was impressed. He said it was a differant feel, equal or better than his z400...
The slip on and filtre ;and jet, makes a diff. as far as i am concerned.
chow

 

WEIGHT makes a huge diference in everything.. You wont gain power with a 400 till you open it up and do some work.. Costs alot of $$ but well worth it. My quad can beat cheaply built 440s. Save the money and build the motor. The pipe wont get any one any where. ANOTHER THING TRX465. oh how i would love to ride your bike. Just once.

 

60lb will make a bunch of dif. However a pipe and rejet will only give you about 1 matbe 2 hp on a 400EX. The EX is pretty well optimized as is from stock. The carb has just about all the air going through that it can handel so without a new carb you will not see much but a w/ anew carb the air has no where to go so then you need a valve job and cam.
Even a cam swap will mostly move the power around not add much, I have tried. The only real hop up fix for the EX w/ power that you will see on a stop watch not just the OH man yeah it is faster that comes from it being louder is to go bigger I have ridden the 440 kit with a new carb and it make a real difference w/o the card it had a lot more torque but was not any better on top, the only problem is after about 5 laps you can feel the power drop off due to heat.

 

GRIM REAPER WHAT WAS YOUR STOCK JET WHEN YOU BOUGHT IT??

 

I've said this over and over agian, a pipe on a stock 400ex engine is a waste of money. $250-500 for 1-2 hp, wow!

 

Try the main jet at about 155 and see if the plug reads good. Also, the 22 in rear tires are not helping much in the drag race. What size tires did he have? With the stock engine all that is needed is just the slip on the back. How many discs are you using? The number of discs will also make it run different.