Thinking of picking up a '98 YZ400 -- Should I?

OK, so I haven't gone and seen the bike yet; probably will do so tomorrow night. It's a 1998 YZ400, and the guy is asking $950. It's not running. According to him, "It needs new fenders, and I think the carb needs to be rebuilt." He said he bought it from a buddy, rode it a few times, and now it's been sitting for a while (hence his guess at the carb being the problem). He also said his buddy rebuilt the motor before he bought it.

What do you think? Should I pick up this bike? I'm kind of trying to get a mini-project bike -- but I really don't want a disaster bike. :bonk:

Appreciate any/all input.


Zeke :foul:

PS: Comes with triangle stand and paddle tire(s?). Crappy quality images below.

PPS: Does this bike really require 92 octane as I've read online? 92 octane isn't available in CA. We only have 91 AFAIK.





Edited by ezekielvictor
Added some images.

I have been riding a '98 YZ400 for about 3 years now. Mine was also brought not running and with a 'claimed' recent rebuild. The owner did however have the rebuild receipts and they had been done by a reputable shop.

I got the bike running and it has been sweet ever since. If you scroll through this forum you will see these are good reliable bikes.

It will most likely take some effort to get going, especially if the fuel has been left in the carburettor. You will have to strip the carb and take good care with cleaning out all the passageways, some are very small and may be blocked even though they may look clean. ALso take note of the sticky's at the top of this forum, there is a thread there with video's about how best to start the bike. The golden rule is don't roll the throttle when kicking. If you do it will never start.

When you look at the bike take a look in the airbox - the condition of the box and the filter will tell you whether or not regular maintenance has been carried out.

Lay the bike on its right hand side and take off the timing cover (on the left and assuming the owner is OK with this of course). You will be able to feel if there is any movement in the crank bearing or not. If you cannot do this, drain the oil and see how clean it is and if there is any metal in it (you can simply refill the bike again once this is done so no harm done if you don't take it).

Check the radiator fluid level and if the fluid is clean (not milky which indicates a potential head gasket problem). You can also check this by removing the small screw on the right hand crankcase down by the oil filter cover.

Another check is to lay the bike over on the left hand side and remove the oil filter cover - check the colour of the oil and the cleanliness of the filter - again an indication of how regular the maintenance has been.

Generally however, you will just have to go by gut feel, the general condition of the bike, and how genuine you believe the owner is.

Good luck

any bike for that kind of money is gonna be a risk. if your mechanically minded you could chance it.

The bike requires 92 Research Octane. CA pump premium is typically 91 AKI, which is equal to about 96 RO, so there's no problem.

The bike requires 92 Research Octane. CA pump premium is typically 91 AKI, which is equal to about 96 RO, so there's no problem.

Beautiful, thanks. Obviously that would've been a huge issue if it were required/not available.

Thanks for the replies and especially for the detailed pointers, DeeCee. Made notes and I'm planning on checking out the bike tonight. Updates to follow soon. :bonk:


The bike requires 92 Research Octane. CA pump premium is typically 91 AKI, which is equal to about 96 RO, so there's no problem.

I hate when the manual only refers to RON octane ratings, and when your new you think that you need race fuel to run a stock bike!

Reading some of the newer service manuals they now mention the AKI standard first and the RON equivalent second under fuel.

OK, so I checked out the bike tonight. Although I wasn't really given the opportunity to inspect the top end rebuild + carb cleaning (naturally), I did see that there is a new air filter, new brake pads front and back, and new throttle cables, and everything else appears to be clean and in good shape -- good signs to me. The only thing visibly worn out were the faded/crusty fenders.

He started the bike correctly according to the procedure, and it fired right up. He showed me how he had to keep the throttle up in order for it to run (it won't idle). It backfires quite a bit when letting off the throttle, flames included. I called my dad and he suggested that it might be a timing issue. I have no problem working with that.

I'm going to take it from the guy for $900 and go through the motions checking the valves, timing, plug, crank bearing per DeeCee's suggestion, and float height. The guy admittedly had 87 octane in it, too (a mistake on his part, he acknowledged), so that'll be fixed. Additionally, it looks like the new air filter he put in doesn't appear to be oiled. I think when I dial all that stuff in and get it idling/running right, I'll put a new plug in and rejet if necessary.

Otherwise, I'm super excited to get another bike, especially one actually built for racing. So far I've only owned/ridden street-legal dual sports -- not knocking those, but hey, you know how long those street parts last in a race. :bonk:

Thanks again,


So it's coming home or will you think about it a day or so more?

Hey bud, unplug your throttle position sensor and see if it runs without the popping and what not... Same exact thing that mine did and after 2 days of kicking I decided to unplug the sensor and try it. started right up and purred like a kitten. okok, like a mean ass kitten on juice, but a kitten nonetheless :bonk: The tps controls the ignition timing and if its off the whole thing runs like crap or not at all. I've been told you can run without it as it only controls a small piece of the ignition map. You wont notice a difference at full throttle and only a small difference at part throttle.

anywho, good luck, its a fun/hard to handle bike :foul:

So it's coming home or will you think about it a day or so more?

Why? Sounds like you're concerned. :bonk: I actually wanted a cheaper little project bike (little as in not necessarily requiring a huge amount of work), which is why I was browsing < $1000.

I just saw another '98 YZ400 on CL for $1000, running, and with many extras. It's pretty far away from me, though, and maybe has been ridden more seriously than this YZ. I can probably use this other bike as leverage to get a lower price on the not-running YZ.

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