1 reply to this topic
  • downin

Posted November 21, 2010 - 05:22 PM


I have an 09 450f with an fmf powercore 4 slipon with a twinair air filter. The next mod on my list is a fmf megabomb. I know i will have to jet the bike since I luckily slipped by with the stock jetting with the slipon and air filter. What would be you guys best guess on what i should do with the jetting after I get the megabomb. I live in central Pa and ride from spring till late fall in temperatures ranging from 55 to 90 degrees F? Also I am around one thousand feet above sea level. Any help is appreciated.

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

Posted November 21, 2010 - 08:55 PM


I ride from 2700 to almost 6000 feet.

Last fall, I installed a PMB endcap/spark arrestor which helps the stock can a lot, and also installed the Ti Megabomb header. I raised the needle (lowered the clip) one position and was pretty happy. When it got cold out, like around 40 degrees, it was lean at idle, like almost 4 turns out on the fuel screw to get rid of the hanging idle. It was great in the spring and probably a little rich at low RPM in 90 degree weather in the summer. This fall I finally installed a 48 pilot and it is almost too rich at idle, at least until it got below 50 degrees. I am going to put the needle back to stock before my next ride.

Summary: I will put the 45 pilot back in in the spring with the needle in the stock position, and next fall, install the 48 with the needle in the stock position. At your elevation, I would put in the 48 pilot and try dropping the needle for best throttle response, maybe go with the bigger main also. I'm planning to put the bigger main in for a desert race I'm doing in Febuary and see what happens--100 miles of sand wash:bonk:.

Related Content


YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Need help by Goforaride

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  68 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

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.