Hard starting (sometimes) 426

My '01 YZ 426 has gone through nearly this entire year without skipping a beat. Several races, poker runs, fun rides with the family, etc. Normally starts on the first or second kick.

Washed it last week after a ride, started it up, let it warm up, and put it away. Then tried to restart and it won't pop. It has done this on a couple of occasions, and I have had good luck simply replacing the plug, and it starts again. This plug is only about 2 weeks ( and 2 rides ) old, but it won't start.

Yesterday cleaned out the carb (not like I found anything in it really) and cleaned up the contact points where the coil mounts to the frame, fresh gas, and still nothing.

So the question is - Does this happen to anybody else? Is there a better plug to use? Once before I replaced the plug and it still wouldn't fire. Got another new one and - bam - started right up.

Thanks guys.


Are you using a #8 or #9 plug (the latter will foul easier, both are listed in the manual)?

My long experience w/ my '00 and '01 YZs was that they would never foul a plug or refuse to start unless someone unfamiliar w/ the bike rode it, then there was about a 50% chance of either or both occurring.

On very rare occasions a CDI glitch can really eat up plugs, this happened on a KX250 I had and to a friends '01 WR.

Washed it last week after a ride, started it up, let it warm up...

How long did you let it warm up?

It warmed up for maybe 5 minutes or so - just long enough to vaporize any water that may have ended up in the exhaust.

The plug is an 8.

I haven't had this happen to me but I have been hearing about it for many years now...

water,moisture, chemical from car wash, or just the stuff you clean your bike with gets

into the electrical connectors. Corroids and won't let the elecrics work like they were designed.....The fix is to un-plug and plug wiring connectors several times to get the

circuit back the way it should be before the corrosion......this fixes your problem alot of times. hope this helps.


Thats why I seal my connectors with rtv.

Thats why I seal my connectors with rtv.

That's why I don't pressure wash my bike... :cry:

I read your post a second time and it doesn't sound like the bike has restarted this time even w/ a new plug.

I agree about checking the harness connections for signs of corrosion. Lots of plug changes may have also damaged the connection in the spark plug boot, but I'm not sure if you can reconnect or check this w/out damaging the part...

Provided the bike will still not start, have you checked for spark?

Have not put a new plug in it yet again.. Went riding a week ago or so with a new plug, and it has not started since the last warm up after the wash job.

I'll check the electricals.

Check to see if you have a good spark.

BTW: I don't pressure wash my bike. The PNW is very muddy and nasty and wet.

Your plug fouling problem has absolutely nothing to do with with washing your bike (I have been using a 3100 psi pressure washer on my 400's and 426 since day one) Your fouling problem has everything to do with the bike not being properly jetted and balanced. PM me offline and I will give you a complete jetting setup that will resolve your issues.

Bonzai :cry:

I've sometimes had a similar problem. I used to start my bike before driving to the track just to make sure everything was good before heading out. It would start fine at home, but when I got to the track I would wear my leg out kicking it :cry: . After installing a new plug, it would finally start. Now I just go to the track and ride. No more problem :cry: . For what ever reason, I've noticed these bikes don't like to be started and "warmed up" for a short time and then shut down. Others have posted on this problem also. Maybe it can be fixed with a jetting or sparkplug change. I don't know, I never tried.

Another thing to consider is your valve clearances. As your valves tighten over time you will start to have trouble starting it. If this is a new problem and nothing in your routine has changed, you may want to check your valves. It's easy to do and a good idea to check them periodically.

Fox your jetting and you wont have that problem.

When you start the bike after you wash it, ride it a little around the yard. Seems that when this happens to me most is when I start it, not ride it, then shut it off. Good rule of thumb is if you start the bike, ride the bike. Riding it must help clear out the plug from excess gas/oil from stitting idiling with the choke on warming up.

I have been using the #9 plug (at the recommendation of my local Yamaha shop's ace mechanic) since the bike we about 6 months old. No problems with fouling.

Like mentioned...if the bike is not jetted properly you really have a very small margin for error when it comes to the starting routine.

I'll try a 9 this time.. maybe between that and the jetting setup I'm hoping to get yet from the yamakaze dude that will take care of it..

Thanks everybody.


Well the 9 is a colder plug so in theory would make fouling easier. However the mechanic (who also races) said that for longevity reasons he uses 9's in his 426 and now 450's. Not sure if there is anything to it....but he sold me when he said longevity! LOL

I have the same problem with my 02 426. I can go for a two hour ride and then the plug is fouled. It absolutely will not start until I change the plug then it will start the first or second kick. I dropped my main jet down to a 158 but that didn't seem to fix it. I'm going to put in a 152 main jet and drop my needle down a few clicks. It runs great when it has a new plug but I'm getting way tired of changing plugs. :cry: Man I've gone thru alot of plugs!

I believe jetting is key. I raced a '98 400 hard for 3 years and only fouled one plug the entire time I had it. My '04 450 has never fouled a plug(yet! Knoock on wood!) YZF's are very finicky with air screw adjustments. I run a Zip-Ty air screw and adjust it all the time. If it's off only an 1/8th of a turn YZF's can be a bear to start. A new plug is just a band-aid.

I dropped my main jet down to a 158 but that didn't seem to fix it. I'm going to put in a 152 main jet and drop my needle down a few clicks.

If indeed your jetting is fouling the plugs, it ain't on the main circuit. Maybe on the clip, but most likely the pilot and/or idle mixture is the culprit. Mebbe a bad acclerator pump.

What is your elevation BTW?

Being at 4,500 ft. I've put several hours on a few 426s that I knew were too rich, everywhere, and didn't foul any plugs, so I hesitate to buy into this explanation. I also had a friend w/ a plug fouling '01 WR, and no amount of jetting would cure the intermittent, inexplicable fouling. It always happened during starting, also. :cry:

The only plug I ever fouled in my YZF(s) was a BR9, while trying to start it. It makes sense that an 8 will be less prone to fouling.

As long as I've been on this website there have been a few folks w/ problems fouling plugs in their YZFs, a lot of that may be operator error but... :cry:

I'm in Albuquerque - elevation is somewhere around 5000 feet ASL. I've heard several people talk about fouling the plug during startup, but thats not the case for my bike. I put in a plug it starts right up....I ride for an hour or two (without stopping or restarting bike) and then the plug is fouled and the bike absolutely will not start until I put in a new plug. I know its not from riding to slow, cuz I'm balls to the wall most of the time! I use NGK CR8E and have not tried the CR8EIX yet.

Bottom line is, I have finally got a new plug in the thing, and it started just fine.

I did notice though that when I blew air into the hole where the plug goes (before removing the plug) a little water came out of the drain hole in the cylinder. When I removed the plug, there was still a little water surrounding the threads as I looked closely at it. Would water surrounding the base of the plug after the wash cause the starting issue?

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