Check out my spark plug

7 replies to this topic
  • MiniMadMan50

Posted December 07, 2003 - 05:03 PM


So here's the plug out of my '01 WR426.
Posted Image

Yes I know this color is NOT IDEAL. My question is, could my mainjet be the problem? The pilot screw is very rich right now (bike won't even start with the choke on, it's so rich) but once I get the bike started cold, it wants the choke on. I have the stock pilot jet, but a 160 main in it (originally had a 158 main in it for high altitude). when I came back down to my altitude [2200'], a 160 was all I had in my garage.
Let me say right now, that from the START I was always worried that the 160 was too lean for this altitude. The yamaha mechanic that helped me rejet for 11,000' told me the main jet would be fine down here, but I'd need to richen up the pilot screw..
So, do I need to go back up around a 170 main?
I haven't gone on any rides since I brought the bike home from high altitude. Just fired it up and rode around my neighborhood. Any suggestions?
I live at 2200', it's anywhere from 50-60's lately, and humidity is in the teens. Thanks! :)


Posted December 07, 2003 - 05:08 PM


I typically run around a 170 or 172 main in my '01 at sea level. I would guess maybe 1 size down for the addtl 2000'. Of course it is a little colder where you are so on second thought maybe the same size would be ok. A 160 sounds pretty lean to me.

  • blackie

Posted December 07, 2003 - 07:46 PM


Looks lean. Any symptoms at 1/4, 1/4-3/4, or full throttle?

  • MiniMadMan50

Posted December 07, 2003 - 09:14 PM


Looks lean. Any symptoms at 1/4, 1/4-3/4, or full throttle?

I haven't been able to really test out full throttle. Bike is very loud, and I don't want to upset my neighbors.
It revs fairly quckly (slight hesitation if I really crank it open) and there is a little bit of "popping" when I roll off the gas, and/or slow down in gear. Very similar to what a car with a performance exhaust system does.
It runs better with the choke on, at least at 1/4-1/2 throttle. There's a long stretch of road where I would shift into 4th, and just be rumbling along, and I'd pull out the choke, and the bike would respond nicely to that. Not a huge burst of power, but you can tell it was thankful. Temperature is only going to get colder out here, so I'm thinking maybe 168-172 range for the main? Also, do you think I'm going to have to mess with the fuel screw after I change the main jet?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • John_H

Posted December 07, 2003 - 09:53 PM


here's my really lean pilot. PICTURE
since YZ timing, I've had jettin issues.

  • MiniMadMan50

Posted December 07, 2003 - 11:07 PM


Wow that is lean. What do you think about mine?

  • tctrailrider

Posted December 08, 2003 - 06:45 AM


It runs better with the choke on, at least at 1/4-1/2 throttle.

You need to raise your needle to richen up this throttle setting.

  • GrahamO

Posted December 08, 2003 - 08:55 AM


I run a 170MJ at sealevel and I leave it in for loops with max elevations of around 8000'. My plug is so pretty it brings tears to my eyes. (I think my PJ might be on the rich side.) Thats with temps in the 50-80 range and So Cal humidity...


Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.