Bought a 1999 yz400f

Hello TT users!


I have joined the yamaha family! Picked myself up a 1999 yz400f for under a grand. It starts first kick, no choke, and starts within 3 kicks hot (with the hotstart pulled). Did an initial oil change (yamalube 10w40, approx. 1.7 liters) and coolant swap (Peak 50/50 pre-mixed coolant). Old oil looked brand new, no metal flakes. Makes no weird noises from the engine. Clutch pull is heavy, brakes feel very good. Idle is a bit rough, has slight surging/hesitation off idle when accelerating, runs great once you sink into the throttle. Excel rims, new dunlop soft-intermediate terrain tires, new x-ring chain + renthal sprockets. WC frame guards, gripper seat cover, renthal twin walls, moose filter. Has full white brothers exhaust (series 3), muffler pipe is badly dented/folded, around 40% less open where it bolts to the subframe, and it sits partially over the rear wheel so on jumps the muffler contacts the tire. Throttle sticks open, has to be closed with your hand. Has a clean title and tabs.


So, in your opinions, was this a bad buy/deal? It was an impulse buy, I admit it. I currently have only a '98 xr250 for trails and wanted something faster for the desert. Is this a good bike (model). What mods should I do to it to improve power, reliability? Common sense mods? Muffler fixes? Should I just sell it before something goes wrong? Thank you all in advance.


Another thing, the crank breather seems to be routed to the bottom of the frame. My xr had this stock routing until it sucked a liter of water into the engine. Now I routed it up and into a filter. Will the yz400f do this? Thanks!


Edited by Peter S.

Sounds like a pretty good deal to me.....but I am addicted to motorcycles!

From what you describe it just sounds like it needs a little bit of TLC to be back in fighting form too.

Fix that throttle first as these bikes NEED to return to idle when the throttle is released...probably just needs dirt/sand cleaned out and a little

bit of lube, or at most a new throttle cable.

I bet the hesitation and surging are just due to a slightly dirty carb.

The pipe will probably be a little more of a challenge but they can be bent and forced back into shape given enough work.

Congratulations and welcome to the "club"!

Not sure what you paid but the bike looks and sounds like it's fine. Some minor stuff to fix but nothing serious. You may want to throw new primary and main jets in it if it was sitting for a while. It's a cheap fix and made a difference on the starting/idle of my YZ426.

I think my mid pipe is squished a bit around the sub frame too...I'll have to check but this could be by desing. Rear wheel rub happens on the older 4 strokes with the big mufflers on them. You could try bending it a bit back out of the way. The bike might have been dropped on its side and the muffler got pushed over the tire a bit.

Check the valves it takes 10-20 minutes and is worth the piece of mind even if it's running great.

Tons of info here on mods and swaps For the 400/426 bikes. Enjoy the bike. Its the grand daddy of the modern 450 thumpers.

Makes no weird noises from the engine.

Must be something wrong. :smirk:


Kidding aside, YZF's have a rep for sounding like a pipe fitters' convention.  They aren't quiet, but that's OK.   Improvements on reliability? Maintain it well and it's on a par with things like man hole covers and driveways as far as that goes.  Power? forget it.  There isn't enough aftermarket stuff made for the engine anymore, and it already has plenty.  The two biggest raps against it are it's weight and the old suspension.  For the money, hard to beat.

Thank you all for the info! Good stuff to know. I'll definitely get on that throttle cable. And I believe that the pipe is reasonable bent back, although I'm still getting a little muffler rub. Anyway thanks again!

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