WR400F - Changing the spark plug

G'day folks!

As the title states, I need to change the spark plug in my '00 WR400F. Yesterday when I was in the shower my older brother was stuffing around trying to start my bike, and from what I can deduce, he fouled the plug :thumbsup: . Since I've only recently aquired this bike I don't know a whole lot about it. Yet.

Anyway I'd like a hand just to get me started. From what I can see, I'm going to need to remove the side covers, seat and fuel tank to get to it but I'm not 100% sure. What I'm after is a bit of a guide so I don't have to remove more then I have to. Just to be on the safe side, I want to make sure I don't end up dropping any dirt or debris into the plug hole as I'm taking it out, so I'd like a bit of information on removing it aswell. I've done a bit of searching but havn't found quite enough information on the job; I'm assuming because it really is a simple piece of basic maintenance. But hey, we've all got to start somewhere!

Thanks in advance for any help :ride:


Take off side covers

Take off gas line from petcock

Take off seat

Take off gas tank

Take off spark plug wire

Blow air into the hole at the bottom of the head on the right side of the bike, this should blow out any loose debris inside

Remove spark plug using tool provided with bike or a spark plug socket, u-joint adapter and extension should also work.

Teach brother proper procedure for starting bike!

Thanks mate, made things nice and easy :ride: . Anyway I've pulled out the plug, and it was shot. Had quite a thick layer of carbon on it and a slight bit of corrosion around the rim of it; I guess it was definately due for a change. While doing that I noticed that the air filter could definately do with replacing aswell, so I'll buy a new one tomorrow. That aside, any recommendations for a new plug? Cheers, Marc :thumbsup:

Plug Gap is between 0.7 to 0.8mm (3/4 of a mm)

depending on the air filter it may just need cleaning and reoiling, I like UNI filters, the one on my bike is a 2 part - inner and outer foams of different densities - works very well and the inner never seems to see dirt.

Get a second plug and carry it with you, when they die, it's usually the last time they will spark and you'll be stuck without one.

Other things you should do:

Check your sprockets/chain and chain tension.

Check your brake pads.

Change your brake fluid

Check your rad fluid and overflow, mark your overflow level until you become familiar with the bike.

Check your valve tolerances (very important on a "new to you" bike).

Clean the carb unless it's running beautifully.

Check your cables for fraying - throttle can stick if it's worn.

Check your bearings - wheels are pretty easy to test, swingarm takes a bit more - I find the only true way to check the swingarm is to remove the rear wheel and shock and move it by hand see if it binds at all

set your sag

set your suspension back to factory stock and work from there.


Download the manual from here:


Also check for teh mods and do them if you want.

Anything I mentioned above - we can help you with it here.

sorry to butt in the thread, how much static sag should you have on the rear and how do you get rid of excess. thanks Rob.

Check the link to the manuals above - not sure if it changes from bike to bike.

To get rid of excess sag, tighten up the preload ring on the spring

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