Changing Sparkplugs.

I was wondering how you access the sparkplug on a 2000 YZ426? The parts person at my local Yamaha shop told me you have to remove the gas tank, is there an easier way? Also how often should you replace the spark plug?

That is correct, you need to remove the gas tank. It comes off in about 45 seconds once you know where the bolts are. When you get to the spark plug you will see why you must remove the tank.

Also get yourself a long swiveling extension (Sears has them for a few dollars) and a spark plug socket with a small rubber ring inside (the kind that grips and holds the spark plug when you turn it upside down). It's a long tight reach to the spark plug but with these two items changing it is a snap.

A new bike is supposed to come with a spark plug tool, but mine didn't and I use the union as sir said, still a little hard to get to. Be careful so as not to cross thread it when you go back in. I have some fuel line that I slide over the end of the plug to drop it in and get it started, seems easier to feel it getting good threads this way...

I have heard that with the tool that comes with the bike, you don't have to remove the tank. I just pull the seat, take out the two shroud bolts in the radiator, two tank bolts, fuel line and it's off.

Also before you pull the plug blow air through the hole in the side of the barrel to get all the crap out, so it doesn't fall into the combustion chamber when you pull the plug.



99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, EKP #4, 50PJ, 175MJ at 500-1000' Thanks James Dean!

My dealer included the spark plug tool with my bike and it works better than anything I've been able to assemble from my tool box...and I have a ton of tools. Bill gives excellent advice. I might add a little here. That damn cap is hard to get a grip on to remove so I found that by shooting a little compressed air through the side weep hole, the cap pops up about an inch or so. After you get the cap off and blow air through the weep hole, break the plug loose and then blow it out again. More junk comes flying out. A light coat of di-electric grease on the outside of the cap will make removal a bit easier next time.

As for how often,

I've read in here that some guys change once a year. I do it every 6 mos.


I believe the tool that was supposed to come with the bike only costs $10. It us much easier to use than the swivel socket and extension that you would get at your local tool shop.

Thanks for all the replies, it looks like I'm going to Yamaha tommorow to the get that tool. I don't want to damage my motor. At least you only have to change it every six months to a year, unlike a two stroke. Kind of off topic. Last night I took out my Honda CR500 and I just don't like the way 2 strokes make power after riding the 4 stroke, the Yamaha is so smooth and easy to ride.


Once again great info. The air pressure to blow up the spark plug cap is great. I remember Clark saying how much one cost :)

Althought since I have YZ timed my bike and used the EKP jetting configuration that James Dean worked so hard on. I have no reason to change plugs :D


I'd like to add that if I have to change the spark plug in a hurry that I use a socket extention to just prop the tank up near teh can still get to the plug and you don't have to disconnect the gas line.

<font color="Navy">My bike came with the spark plug wrench (two top end and gasket kits too :)). I can change my plug in about 7 minutes, the only thing I remove is the coil from the frame. The plug cap comes off with little effort, then I drop the wrench onto the plug, loosen it with a 14 mm Wratchet Wench(very handy)and pull it up and out through the space between the radiator, gas tank, and frame. VERY EASY!

I have my methods down on how to perform maintenance and starting the beast so I haven't had to change a plug in months. Hope this helps. :D



Toxic, I'm curious, why do you remove the coil to change plugs? I've only done that when I want to tilt the carb to the left and need to have the float bowl not hit the coil. I just don't quite get why you need to remove the coil to change the plug.

You undo the coil to give you slack in the plug wire. Makes it easier to get wire off plug and out of the way.

I think I see now. You need the extra slack to get the plug cap off with the gas tank still semi-on? Is that correct?


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