07 YZ450 Jetting

5 replies to this topic
  • Ripp_

Posted April 05, 2007 - 08:33 PM


I am having a hard time jetting this one. Here are the stats:

2007 yz 450
Uni filter & cage
stock exhaust
48 pilot
Fuel screw set at 1 1/2 turns out
Stock jet needle
165 main
2300 ft elevation
80-90 degrees farenheit
Premium pump gas

The motor surges from 1/8-1/4 throttle when not under load. It runs great everywhere else. I have tried richening the jet needle all the way to clip 7 and also tried the nflp & nfln needles top to bottom. I adjusted the plug gap to .030 from .023. That helped a little. Help!:bonk: :naughty:

  • grayracer513

Posted April 06, 2007 - 08:01 AM


Your "air screw" is a fuel screw. In for lean, and out for rich. Low throttle openings such as 1/8-1/4 are influenced more by the pilot circuit than the needle, and your fuel screw setting seems to me to be in too far. Back it out to around 2 turns, and start there. You should review the procedure in the manual for setting it.

Otherwise, the jetting looks like what most people are running.

  • Ripp_

Posted April 06, 2007 - 10:35 AM


Sorry I ment to say fuel screw. It is set correcty. I turned it in untill I had a lean mixture RPM rise, then back out a little bit.

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  • Dizman

Posted April 06, 2007 - 12:19 PM


At your altitude, I think your jetting is a touch on the rich side. At my altitude here in CO at 5280 ft, I have a 150 main jet, 42 pilot, needle at stock setting, fuel screw 1-1/2 turns.

At your altitude in AZ, I would try a 158 main and a 45 pilot.

  • AZcrRider

Posted April 07, 2007 - 07:09 PM


I am in AZ, almost the exact same temps/elevation. Stock exhaust. Running the spark plug gap at 28.

I am at stock jetting:

160 main,45 pilot, NFLR on the 4th, fuel screw is 1.5 out currently. ( adjusted today at Ocotillo, about 82 degrees out)

Seems to run pretty good with no bogs or weak spots in the power. Hopefully, when monsoon season hits and it is 104 with 85% humidity I won't have to rejet ( like the old 2 stoke), but we'll see.

  • kyle450rider

Posted April 07, 2007 - 10:22 PM


From what i've seen this bike is hard to jet.Everyone i've talked to at the track and trail has said that even though they got the sweet spot now doesnt mean that its for good.I think this bike needs constant attention when the temp moves more than 2 degrees.Funny,i didnt think 4 strokes were so finicky on the jetting.

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