2009 YZ450F Jetting

4 replies to this topic
  • WR450F_No28

Posted October 26, 2010 - 03:35 PM


I have raced a 2006 WR450, for like, forever. All sorts of things, mx (am not too good at), GPs, Idaho City ISDE qualifier, 24hrs (even Ironman), etc...on and on, lots of races, rides, torture...and other than the WEIGHT and I had to replace the starter, I love the bike! Jetted it right from day one (GYTR powerup kit...just flat worked.)

I am a weenie, 175lbs, race 40A and am pretty competitive in this class and on the WR...until the wife got tired of my moaning about its weight and bought me a new leftover 2009 YZ450 that is, in a word, awesome! Racing it is a blast, suspension is unbelievable, and i am smitten big time. I have set it up for off road (armor, tank, etc.)

However..I do a LOT of dead engine start races and am having trouble getting the jetting right. I messed with lower pilots, quite a few "cheap and sensible" things (fooling with needle, pilot, fuel screw.) Right now, am back to stock everything, have Tusk adj fuel screw, but have a 48 pilot in (which HAS helped!) I run a Lexx Rocky Mountain pipe which tested 94.5 at Big Sky XC so am happy with that. I am getting great fuel mileage from it and plug is looking right, nice and tan. Bike runs almost too good...just not what i would call an easy/fast starter.

WR starts hot or cold just flat easy...kick or button.

The YZ "starts" but not "in a hurry"...prefers to be in neutral. Have about 15hrs on it? Mostly fast trail riding and races. Live in Helena, MT elev ranges 3k-8k on riding locations. (Elevation here is 4k)

Have heard awesome things from friends that I race with that run this bike, and all are saying "what took you so long?"

Most are running just stock jetting and their bikes start "fine."

Any directions or suggestions are appreciated! Also, any articles/suggestions on making this bike last and be as reliable as Ms WR450 are appreciated too.
Thanks in advance!

  • grayracer513

Posted October 26, 2010 - 04:02 PM


I run desert races that require dead engine starts, so this is familiar to me. The last thing you want is for your bike to get "stage fright" in the opening scene.

It does prefer to be in neutral, and it will. There's too much clutch drag for it to be kicked through well enough to start reliably in gear. There are a couple of things involved with this, and a couple of things I've wanted to try and haven't got around to yet.

Apart from that, the pilot jet setting and idle speed are key things in making the bike start on the first kick for you. As far as the pilot jet/fuel screw goes, I find this works best:

I set the pilot up by the book as a base line, and follow the general rule regarding verifying the right size ( http://www.thumperta...ad.php?t=327405 ). After that, I lean it out to the point that it will just begin to hang very slightly while idling down with a slightly high idle speed, but only pops on decel some of the time. This, along with the slightly faster idle makes it start easier and also helps keep it from stalling If I suddenly close the throttle and pull the clutch all at once.

The pilot I run in mine is one size larger than the bike came with (45 vs. 42). With the higher altitude, yours might be a bit too big, maybe not.

At my races, everybody warms up their engines as they line up or before, and are told to shut down. The banner goes up for 30-60 seconds, then drops. I find that this works best:
Shut the bike down and wait. When the banner goes up, but not before, I push the starter through to the compression stroke, and reset the crank, ready to kick. This gives it a fresh intake stroke just before starting, and it usually lights right off.

It's mostly a matter of finding the right recipe for yours and sticking to it, really.

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  • WR450F_No28

Posted October 27, 2010 - 06:31 AM


I am pretty sure (dont have my notes in front of me) my 09 came with a 45 pilot. I tried a 42...did not help. A good buddy that runs a shop in Kalispell that has had them on the dyno told me to go UP on the pilot..so i did (to a 48) and it DID help. I have not tried the idle idea yet, but i "should have known". I have a long history of bad dead engine starts (raced a modified CR500(bought it that way..previous owner scared of it) for a long time...THAT bike was hard to start!)...then went to the WR....end of that problem.

Well, it is back in the YZ (see my start at the Big Sky XC AMA western hare scrambles event...second from dead last)...sometimes it goes, sometimes it doesnt. I make up for it (ran 2nd laps 1-3...crapped out lap 4 and finished 8th)...but need to figure this out. THANKS for the notes!!

  • Dick Falcon

Posted October 27, 2010 - 06:45 AM


well i ride a 09 offroad,so heres my set up.fmf q with screen removed,powerbomb header.jetting is 48p stock needle in the 4th clip,165 main.it dead engine starts great,hot starts in 2-3 kicks.I always start in 2nd gear.i do run a rekluse pro,so that might help.Oh i'm at sea level,and temps range from 10-100 deg.lol

  • grayracer513

Posted October 27, 2010 - 07:14 AM


I am pretty sure (dont have my notes in front of me) my 09 came with a 45 pilot.

It did.

You may want to browse through this thread, see what others have done:


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