Check out my spark plug

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


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! :)

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.

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

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?

here's my really lean pilot. PICTURE

since YZ timing, I've had jettin issues.

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

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.

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...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now