Thread: Yamaha WR400F
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Old 11-12-2012, 04:43 AM   #161
wannabe bike builder
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Joined: Jul 2010
Location: melbourne Australia
Oddometer: 223
Laugh bike mods and experiance

Originally Posted by MingRidesBikes View Post
Thanks for all the info! I'm gonna be reading into the carb and ignition mods. Didn't think these would be substantial area's of opportunity. I do need to check the throttle stop screw for sure. I know it has the yz pipe I believe off an 2001? they are different between 01 and 02 if I'm not mistaken. And when doing the hotcams from the 426f, The exhaust is for auto decomp, the intake is where the power comes from correct? Jetting I'll have my shop dial down, is there an airbox mod that actually helps this bike breathe and get more power, or keep it stock?
These have heaps of power stock most of the mods are for rideability.

Carb mods make the bike pull throughout the whole throttle action, this model was renowned for an awful bog when the throttle was cracked open hard.

yz pipe increases responsivness Not much difference just an end cap and length I belive

Exhaust cam is 100% for the auto decomp this helps the bike because with out the cam they used to stall all the time in the woods when you would rear brake slide into corners the auto decomp cam totally eliminated this problem, However i did notice a small power increase down lower but could be mistaken

Keep the airbox stock.

You can get lots of power out of these,at one stage, I had a head that was fully ported with Kibblewhite diamond coated ti valves with a prox high comp piston and had a lightened yz flywheel vortex ignition with a raised rev limiter and the bike was an absolute weapon to ride, too much to handle then I dropped the high comp piston and put the wiseco 450 kit in it and then it was worse. All this pursuit for horsepower just ended up costing a bomb because I destroyed two complete heads. I have put nearly everything back to stock, kept the vortex ignition because it has two settings max tourqe (slippery conditions) and max power and it never comes off the max tourqe setting.

I was at an enduro and an old racer said dont spend money on motors spend it on brakes, tyres and suspension then go learn to ride. So I heeded this guys wisdom went to some riding schools and now brake much later and carry more corner speed and still round up most on the track and trail. Guys with the new bikes (especially the 16yo's) hate it when they get passed by a fat guy on a ten year old bike bike with a bad rep for being too hard to ride.

Try this carb setting (may not work real well in US)
standard yz needle (3rd from top clip)
38 pilot jet
165 main
1 3/4 - 2 turns out on the air screw

Bear in mind I have my bike running quite lean and I have tried the jd jetting kits and there recomended settings are way too rich for our fuel quality (quite a lot of setting on american forums dont work real well in Australia dont know why)

Build it and you will ride

My crazy bike build
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