yz400f to supermoto and

as the title says, i have made my yz400f into a street legal supermotard. i am having small issues with it though, probably because of its age.

my first issues is with my rear brake, not only do i have drag to it but the rear pressure switch is staying lit after several minutes worth of riding. now that i think of it i think thats pretty much my only problem!

i would like to get a little more power out of this bike if possible and was wondering what you guys think would be the best bang for buck. i have a white brothers pipe on it already and a light weight piston from what i am gathering but that would be it. this winter i am pulling the engine out and getting everything powder coated and prettied and want to go through the engine. nothing is out of range for me so let me know guys. big bore? cam? high compression?

oh it also has a 03 yz450 carb on it that i have been fine tuning lately.

anyone? looking for a little insight here guys so i can start buying parts, to get prepared

Leave it more stock than not if you want it to last on the street. Play with the gearing more than anything. Maybe even consider a WR bottom end while you have the motor out this winter.

what about bumping up the compression a little, maybe going with a small cam. leaving the bore alone? and what would the wr bottom end do for me? whats the difference

what about bumping up the compression a little, maybe going with a small cam. leaving the bore alone? and what would the wr bottom end do for me? whats the difference

before you spend that money, spend money on getting a slipper clutch and a cush drive.

Both will save you lots of $$$ in bottom end wear

At that age, the rear caliper probably needs a rebuild - new piston and seals, and clean up the pin. Might make a world of difference. Maybe $40 for the parts, tops?

I'd also try to get aftermarket radiators and perhaps a fan assembly somehow. I dont think these bikes like to be standing still.... (traffic)

the bike is insanely smooth to begin with and yes slippers are fun but they make it difficult to pick up the front end when you would like to. i mean it already can't be picked up in third which i think is because of the weight of the bike. my buddy's 450 husqvarna has a slipper on it and its fun for a little while.

I'm planning on disassembling the rear caliper soon. is there anyway to get more air to this bike? I'm quessing the only way would be to cut some big ol' holes in the air box.

in 2 weeks i have already but 550 miles on this beast and i am loving every minute of it. bike starts every time. has plenty of power and its taking me a little while to get comfortable to and use to leaning with the bike through corners as opposed to weighting the outer peg in the dirt lol but i love it!


this is the bike without the black front fender. will put better pics later

i have really been thinking about the radiators guys. who makes a radiator for the 1998 yamaha yz400f? as far as i know fluidyne makes badass radiators but cannot seem to find a radiator to fit my bike. if anyone knows of them please let me know because i cannot find a set of aluminum radiaors.

As far as I know, YZ426 radiators will bolt on. See if they have those.

any one have any ideas?

Check ebay there are Chinese made ones for about $100/set.

just wondering but my yz400f with the 450 carb is running with yz450f's and husqvarna 450's right along side them. so what would the 426 head and higher compression with a aftermarket crank that could handle the extra power due for me?

i know you all are going to say that i would be better off getting a new bike because i will end up dumping a ton of money into a dinosaur but my family has had this bike since it was brand new and has never ever ever had any problems. my dad rode the shit out of this thing for 10 plus years until recently and he rides at a 1a endure pace. or whatever level the big dogs are in enduro.

could i go 426 and still keep my manual decompression? could i cam the 426 and keep my manual decompression?

Using a 426 head will not affect the engine size. That's a function of the cylinder bore.

You can use 426 radiators, but then need 426 shrouds...the lower front attachemnt is at a different angle...

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