2007 power flat, jetting?

6 replies to this topic
  • Family Man

Posted September 27, 2012 - 03:58 PM


I recently rebuilt my 2007 yz450f. Had the head redone with stainless valves, springs and polished up. I also installed a High compression piston 13.6 : 1 and new timing chain. Starts first or second kick but the power feels mushy and flat. Im thinking the power should be crispy and pull super hard. I have a 165 main 48pj and stock needle in the stock position, 3rd. Stock exhaust back on. Im under 0-2500 feet in Northern Cali. Im thinking of trying a 170mj and maybe the needle in the 4th clip?

  • Family Man

Posted September 27, 2012 - 05:24 PM


I tried a 162 main jet and it was worse. The 165 feels better, seems to pull harder. Im going to try a 170mj. May also try a 45pj, I dont notice and decel popping

  • Family Man

Posted September 27, 2012 - 06:08 PM


Needle looks like a pain in the @#s , any tricks to get at it? The Manuel reads like I might need to lower the needle a clip. page 7-10.

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

Posted September 27, 2012 - 08:57 PM


Pro Circuit recommends these jetting specs for stock 160mj 45pj NFLR 4 clip : I'm going to give them a go.

Edited by Family Man, September 27, 2012 - 09:00 PM.

  • grayracer513

Posted September 28, 2012 - 08:52 AM


Pull the top engine mounts to access the needle. Remember that the needle (the taper and height) is most effective between 1/4-3/4 throttle.

The recommendation for a 160 seems wrong given that you said the 162 made it worse. 45 pilot sounds right, though.

One of the effects of higher compression is that the intake signal gets stronger, especially at low speeds, so quite often raising the compression can make low speed jetting richer than normal. On top, it can work the other way 'round since the high RPM intake volume was good in the first place, and the extra compression can make the original jet seem too small.

Check to see if you have anything sitting in front of the main air jet passage at the mouth of the carb that could upset the balance.

  • Family Man

Posted September 28, 2012 - 12:29 PM


stock position of the need is the 4th clip not the 3rd, got my bikes mixed up. Do you think its a good idea to try the 5th position?165 45 NFLR 5? or do you think 170mj 45pj and needle on the 5th?

  • grayracer513

Posted September 28, 2012 - 01:02 PM


You have to get the main and pilot jets at least in the ball park first. The needle is more of a trim adjustment thing, and only affects part throttle operation. The '06 ran an NFPR needle, which is the same major diameter and the same taper, but the taper is higher on the needle by half the difference from one groove to another. That means that NFLR-4 is one half step leaner at half throttle than an NFPR-4. Very small difference, but it validates the idea of trying NFLR-5.

But do the main and pilot first before you confuse the matter by changing too many things at one time.

Related Content


Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

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.