My Bike Is A Spark Plug Eater!

My 02' did the same thing since new as well. I used an ega machine and found that it was running way too rich. The exhaust gas analyzer read the bike was way rich on bottom and in the middle, so I dropped the needle one clip and turned my pilot in. I think its at 1 and 1/4 out. Been running killer ever since. I wish I had extra cash to buy an ega machine. Hope this helps. :naughty:

Would loved to get mine checked out - where did you get to check it on the EGA? Anybody offer this as a service?

have you ever tried an iradium plug before, that might help too, just a thought

I work at a local Yamaha dealership as a tech. We luckily have one and it is the best thing to help set up carbs. It takes out all the guess work.

My 05 YZ 250 used to do it too, so don't feel so bad. I would go through at least one plug a day and it got so annoying.

Anyways I finally fixed it by leaning out my jetting and changing my Pre Mix, but you got a fourstroke so all you got to work on is your jetting.

Mine was rich, so Im assuming yours is too, so lean it out some and it should stop fouling plugs.

I was out looking at my spark plug tonight and it looks a little on the black side. Does this mean I need to drop a size on the main or the pilot jet? or would it make any differance if I just raise the clip on the needle one position?

May be too simple, but same thing happend to me when I got mine. I was starting it wrong by twisting the throttle. I don't now and the plug never fouls.

I worked through all the free mods, fuel screw, etc for my '02 426. Still fouled plugs, until, as Sleeman put correctly, Pilot Jet! Haven't fouled a plug since.

Bad gas. Dump it and grab some high octane. Keep a look out for some race fuel at local gas stations.

I've got a statrion that has unleaded 105. Bike doesnt sputter, no pop, just power on demand. Got rid of that popping and bog after I dumped the crappy gas.

I got a lot of suggestions to adjust carb but I figured before I'd tear into it I'd just drain and try some good gas.

I run 110 octane just because it is stable not for performance. Pump gas always varied depending on where I purchased it, fouling did happen on occasion. A combination of things helped. BK/GB mod first, spotless carb, adjustable fuel screw and making sure I turned the fuel off and let it die when it ran out of fuel seemed to help. Never a problem anymore. Smaller pilot might help also, where is your fuel screw usually set?


I have had every year model of the YZ4xxF since '98 and my 02 did the same thing. I have never replaced a plug in any of my other year models but my 02 went through 34 plugs in 34 rides. I was so sick of that bike. If I let it sit over night and tried to start it the plug would be wet fouled. No pumping the throttle. Same starting routine on all my bikes and the 02 had a problem. We tried new ignition CDI box, coil, carb, stator, everything. Yamaha gave up and said they could not find anything wrong. I sold the bike and never looked back.

I just turned my fuel screw out an extra 1/2 turn and that got rid of my popping on the decel, so I figure it may have been lean. I am now thinking that maybe its rich on the pilot?? I dont understand why the bike chews up the plugs because if I put a new spark plug in, the bike usually starts good in the morning for 3-4 rides. After that, it starts wet fouling the plug again. Do you think that I should try a smaller pilot?

If you are 2 or more turns out on your fuel screw, go up one size on the pilot and turn the screw back in. If less than 1 turn out go to the next smaller pilot and turn the fuel screw out. I read you didnt have a clamp between the pipe and can. That is a big cause of popping due to letting oxygen into the exhaust allowing the excess fuel to relight in the exhaust.

If it sits overnight and wont start the next morning, probably too high of a float level.

Yeah, I fixed the connection between the header and the exhaust and that helped. Since turning the fuel screw out 1/2 turn stopped the popping I am thinking maybe it could be the float level. I am going to take the carb off tonight and check everything over....Thanks for all the help guys! :naughty::naughty:

What plug are you using? I have the same problems.


CR8E... My bike dosn't eat up plugs anymore though. After I did the Cam update and put the White Brothers pipe on, the problem fixed itself. Strange, but at least its fixed.

do the BK mod. I had no idea what it was until I went to this URL and checked out the tech articles:

no wonder these bikes foul plugs - wait until you see how much gas is being dumped into the cylinder when you check your squirt duration...

You might also check the float level and float needle valve. A too high level or leaking valve might potentially lead to plug wetting. I generally run my float level about 2mm lower than stock.

Actually go up on the pilot, you said you turned the fule screw out 2 turns and the popping stopped? That would indicate the need to increase the fuel. Go the next size up and turn in the fuel screw. Do you turn off the gas everytime you stop? And let it run some down? If I dont turn off my fuel between rides or sessions it is a mf to start. Havent done it in years since I turn it off religiously. The Bk mod I dont think is applicable to the 02. Try JD (James Dean) on the jetting forum, he might have an answer. Have you thoroughly cleaned your carb? with air also?

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