Starting Problems WR426F, advice needed

27 replies to this topic
  • trick202

Posted October 20, 2004 - 02:35 AM


Just out of interest, would all this advice still be valid on a 99 YZF400?
My old man has one, and it plays similar games to this. Some "expert" has taken most of the electrical system apart and told us that the stator is the only thing that can be at fault.

I had a try at fixing it myself, but I didn't have the special plug tool that comes with the bike, so I couldn't get the plug out. I took the cap off and tried a different plug in against the frame to check for a spark. It was fine.

Sometimes it would start, others, no. I checked it one day, and it cracked up perfectly, so I went to get all my gear on while it was warming up. All of a sudden after about 2-3 mins of ticking over, it stopped dead. Wouldn't restart, not a thing.
I recall when it went to the local bike shop for service and a new plug, it started fine at first and then refused.

Anyhow, I have the plug tool now, the knowledge (thanks to you guys), and some more stuff to try!

Cool! I have a 250 EXC KTM at the moment. I love the ease of the 2 stroke, but I'd switch back to a WR in a shot if I thought I could get the starting sorted.

For my father's sake, is it possible to change the timing back to WR settings from YZ settings? What's involved? WIll it make it more dosile for him?

  • jwriott

Posted October 20, 2004 - 07:02 AM


You can change the timing to WR very easily. Do a search for Motoman393's site and follow the instructions in reverse.

Matt, do a search for LarryCo in the WR forum, he did TONS of jetting work on the 01' WR426 and I benefitted from this a lot. My bike did exactly the same thing yours did. I think with the vast altitude changes we ride in here in Colorado along with the the extreme changes in temperatures, the bikes just seem to flood easily.

FIRST, pull the carb and do the BK mod. Mine was squirting 3+ seconds and I reduced it to 1/3 second. Clean everything very well.

I ended up using this jetting on my 01' WR426 with great results:

Carb Settings (Per LarryCo and Taffy)
- 155mj
- 38pj
- EKP#3 Needle
- 160MAJ
- 65PAJ (Adj), 2 turns out

I used a 152 main for 10,000+ feet and a 160 main for Moab. I rarely fouled a plug with this jetting.

Also, go by Harbor Freight and pick up a pneumatic spark plug cleaner. They are about $10 and will save you a lot of $$ till you get the jetting straightened out. I'd also go back to the dealer and tell them you want some cash back for a problem they did not fix. Most of the Yamaha shops I went to looked at me like I was out of my mind using this jetting and you may have to go to for some jets.


  • jwriott

Posted October 24, 2004 - 03:25 PM


Kranswall, any update on your progress?

  • kranswall

Posted March 30, 2005 - 09:01 PM


Yikes sorry, kinda fell of the face of the earth for a while there. Update is that the bike is running and starting great. With the weather getting tolerable I hope to be doing a lot of riding soon.

Long story short the problem seemed to stem from a number of issues, perhaps all caused by old gas and oil seeping from the filter. After everything was cleaned out, with new gas and plug installed everything is good.

With the starting problem out of the way I had to find something else to tinker with :naughty: so I have installed a skid plate, baja designs exhaust baffle, and did my first oil change.

Thanks for all the tips, very helpfull. :naughty:


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  • Fryboy

Posted April 01, 2005 - 06:47 AM


:naughty: Sweet, another TT happy ending.

  • jbhwr426

Posted December 15, 2008 - 12:05 PM


Just wanted to add a quick note to your thread. I too have a wr426f 2002. i have not had any problems since i bought the bike new in 2002. i am having a very similar problem. I checked my sparkplug it was good but i changed it since i was in there also i cleaned the carb nothing seemed to be wrong but i cleaned it anyway. I still had to bump start it then when i turned it off it restarted 1st kick each time. my problem is that after im off the bike the next day i have to bump start it again. it works like this all the time once it is bump started in the morning it will start easy for the rest of the day until the next day. also once it starts it runs great and idles great too. cant quite figure it out so i will be watching to see the answers you get on your thread. good luck Jeff.

  • tcmII

Posted December 16, 2008 - 05:07 PM


I had a similar problem with a '98 WR400. I bought it in the winter and let is sit until spring. I went through a lot of trouble with bad gas, clogged jets, dirty/stuck accelerator pump shaft and (found later) an improperly adjusted float.

Fixing the first few problems got the bike running, but I went through plugs like crazy. I would put in a new plug, the bike would start and run all day, the next time out the bike would not start until I put in another plug. The plug I took out would be black and wet.

I decided to go back through the carb a found the float to be off (high) by 4mm. Since correcting the float height I have not replaced a plug and (go figure) seem to get better gas mileage. The bike also starts better when cold.

  • Strattos

Posted December 16, 2008 - 07:13 PM


Just wanted to add a quick note to your thread. I too have a wr426f 2002. i have not had any problems since i bought the bike new in 2002. i am having a very similar problem..

I had similar problems with my '02 426, and it ended up being either a dodgy resister in the plug cap or the plug lead.

Kept fouling plugs (rich looking), except in my case, the indication I had that my plug was going was power began breaking down in the mid-upper rev range.

Stuffed around with jetting for six months, including replacing needle, emulsifier and going up and down the jetting scale in terms of needle position, needles and main jets, also bothered 'Burned' from the TT Jetting forum about it for weeks, but to no avail.

Wasn't until I checked the readings between coils and plug cap that I noticed the secondary coil reading was RIGHT off, very low, which meant it wasn't burning properly in the mid-to upper (i'm guessing), and was running stupidly rich and fowling. After replacing plug lead and cap I had no more problems for the life of the bike, which I've now sold and upgraded to an 08 WR. Hope this helps.

Both are absolutely magic bikes.


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