Top ten upgrades YZ400F

Just got a 98 YZ400F and want to make sure it's up to speed (pun intended). Any suggestions on what the top 5 or 10 "must have" upgrades should be for this bike? (75% trail, 25% track). 450 Exhaust cam is the only one on my list so far.

It has quite a bit already, that's why I bought it. Looked over this site the past week since I've gotten it and most of you have things I've never even heard of...Any direction would be greatly appreciated.

So far it has:

WB eSeries pipe

Magura hydraulic clutch

Excel/Talon wheel sets

BBR Kickstarter

Applied Racing triples

ProTaper bar and mounts

BBR Aluminum subframe

Handful of other cosmetics (carbon fiber covers, etc.)

Zero done to the engine and carb as far as I can tell.

Well ride it first and get an idea of what you like/don't like. On my 450F I didn't like the bottom end (none compared to my 525) and how easy it stalls. I rode a 2001 426, and it seemed better for off-road use.

First things I got were:

o Kick-it stand (for trail riding, CC racing (lemans starts)

o 16oz Steahly FWW

o FMF Q exhust (actually had a PMB first, but was 99db, so I couldn't ride it at the local OHV, or races.)

o Suspension work

But on a used bike I'd save $$ for repairing worn out stuffs.

Good luck,

Scott's Stering Stabilizer (SP) :cry:!!

after the exhaust cam definitely do the suspension

sounds like you have the bolt on bases covered if you have any carb probs and need to rejet go with a james dean kit. then set up your suspension. then if you feel you need even more power a 420 would help in that department.

I would get the handy "ZipTy" Fuel adj. screw for easy tuning on your fuel screw

and then DO THE SUSPENSION The greatest thing you can will take it from being someone elses bike to being your bike.

Dont pump another nickel into it until that is done.


Ditto on the flywheel weight. I put a WR flywheel (and stator for 130 watts worth of lighting power) in my '99 400 and it really did help in the tight sections. I agree, suspension should be number one though. Also, if you're really into offroad, an 3.4 gallon IMS tank would be a good addition.

Top things to do to a six year old 1998 YZ400F:

- replace the carb accelerator pump diaphragm and clean the accelerator pump passages.

- replace the front wheel bearings, they are junk.

- rebuild the rear brake master cylinder and replace the caliper piston. They are made from a phenolic material and tend to crack.

- check the steering head bearings. The hot oil in the frame tends to make the grease run out and the steering head bearings run dry.

- replace the swingarm thrust bearings and washers. 99% chance they are worn out. Check the linkage bearings while you are down there.

- replace the water pump seal and shaft with the updated 1999 parts.

- install a fresh counter balancer key if it hasn't been done already.

- If the bike has been ridden consistently since 98 without engine work it's due for a new cam chain, a new piston, a crank rebuild, and new valve springs.

If you decide to go to a big bore use the 426 rod and an OEM 426 cylinder and piston. The 420 big bore kits use a 94mm piston that is much heavier than the stocker. Running the heavier piston on a six year old original rod is a recipe for a disaster.

They are great engines, probably one of the best ever, but they still need some maintenance to stay alive.

Take care of this stuff and you'll love this bike. Even when I bought my CRF450 I kept my 98 YZF. It's too good a bike to part with. :cry:

Thanks everyone for your input. Most things I can tackle myself over the next several months I hope. Rich, that's some good info on the kind of things that get overlooked and can ruin a weekend ride. :cry:

If I get that deep into the engine i'll probably do the exhast cam upgrade too.

Big upgrade from my XR650L anyway!

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