How do I tell if I am too hot/lean

8 replies to this topic
  • Anchslayer

Posted August 29, 2006 - 03:53 PM


I have a new US model 06 WR450 with stock jetting, I took out the exhaust baffle, airbox plug/snorkel, disconnected the grey wire and cut the throttle screw down to YZ specs. I followed the break in procedure and now have about 40 miles on it. I ride at sea level average temp 50-60 degrees and the bike runs great. :thumbsup: Throttle response is crisp and the motor pulls strong through the entire RPM range. I pulled the spark plug and noticed the white insulator was still white, not tan like the manual states. After browsing this forum and contacting my local Yamaha dealer it sounds like I am too lean. My dealer told me to lower the clip on the needle but of course it is not adjustable. There are no YZ needles in stock and no jet kits locally so out of desperation to ride this holiday weekend I decided to shim the needle with two .5 mm washers. My questions are: Will 1mm on the needle make any difference? What are the signs of running too lean so I don’t burn it up between plug readings? How long do I have to run to get an accurate plug reading? Thanks

  • clark4131

Posted August 29, 2006 - 04:47 PM


You're on the right track with the washers on the needle, but you likely need to up the main at the very least. The '05 and '06 seem to like the 45 pilot, but with your cooler temps and sea level elevation, a 48 may be the way to go. Check the jetting database for a comprehensive idea regarding where your carb should be set. You're going to want to pick up an adjustable fuel screw at the very least, so you can fine tune things. If you decide to re-jet, go main, pilot, needle and test each change individually to evaluate it. Reading the plug on these 4-strokes is more difficult that on a 2-smoker, as its appearance isn't always and accurate test of your settings...SC

  • Beejay

Posted August 30, 2006 - 05:37 PM


If you're running lean you should be getting some backfiring on decel from the exhaust.

  • Alley Cat

Posted August 31, 2006 - 05:59 AM


Unless you run leaded fuel, plug reading is just about a complete waste of time. I wouldn't even bother.

When lean, your bike will be in asmhatic, breathe hard, won't pick up speed easily, run hot, may backfire.

1mm on needle will make a difference for sure. If it is better now than before, keep on going untill it gets worse. Then you will know where perfect (for that day! :thumbsup: ) is.

Have you set the fuel screw? This is what will tell you if you need to change pilot jet or not...........

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  • Anchslayer

Posted August 31, 2006 - 09:11 AM


Thanks for the reply's.
I run 90 octane unleaded, its the highest I can get. I do not have the fuel screw (yet). I dont get backfire on decel but I do hear a flapping sound that I thought might be the AIS. I have got an occassional backfire when I shut it down. I have a temp gun that I could check my head temp with if I knew what normal temps should be. According to the jetting DB it looks like I should try a 170 main if this needle adjustment isnt enough, is 168 stock?
So it really kind of sounds like I may be chasing a problem that doesnt exist. The bike runs great I only though it was lean because of the white plug reading. I just want to do everything I can to keep from damaging this bike. I hope to ride it for a long time.

  • clark4131

Posted August 31, 2006 - 11:38 AM


Stock jets sizes are 45 Pilot, 165 Main, 65 Starter, 50 Leak...SC

  • Anchslayer

Posted September 08, 2006 - 01:19 PM


Ok, I rode last weekend with the needle shimmed and it did not make any noticeable difference. I am still too lean. I did the plug reading on my bike and my buddies WR250 and his was golden brown and mine was white so it appears the plug test is at least partially valid. I managed to get my hands on a 168 main and a 48 pilot but could not get a Zipty fuel screw or adjustable needle. Anyone know if the stock needle position will be ok with this jetting or should I leave it shimmed. Also what setting should I use on the stock fuel screw while I have the carb out and can adjust it easily? It is currently set to 1 3/4 out. Thanks.

  • OneToGo

Posted September 08, 2006 - 06:45 PM


Try fuel screw at 1.5 out with the bigger main (168) and Pilot (48).
I think the #48 pilot will work best if you have done the airbox mods and deristicted the pipe.

The adjustable screw will help you - a must do...

The needle really needs to be adjustable. I got one with my bike. Some come in the AIS kit or you can go JD as I did, RED works best in warmer conditions.

At the moment your shims should be OK.
OEM is unadjustable and the needle position is the same as clip in the middle or #4 position - I just checked.
I measured it and the distance between #1 and #7 clip position is 5.5mm - i.e. 6 alternate positions = for 5.5mm. That is close to 1mm per clip so your 1mm shim is the same as needle with clip #5 position (from the top)- so when you get your adjustable needle you know where to start....

  • Anchslayer

Posted September 08, 2006 - 07:22 PM


Right on, I will give that a try. Heading out to the garage now. Hope this works cause I have a 2 day riding trip this weekend. Thanks.


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