fmf 4.1 muffler w/ megabomb jetting questions?

4 replies to this topic
  • bodnar44

Posted November 27, 2010 - 01:28 PM


I have a 09 YZ450F and I just ordered the megabomb header w/ 4.1 muffler. I went to FMF website and looked at the jetting section and they had no jetting chart for my bike. Dose this mean that the stock jetting is correct?

  • Steel Panther

Posted November 27, 2010 - 04:26 PM


check out the sticky on jetting. I have an 09 with the 4.1 and megabomb at 700ft. I went to 165 main, 4th clip on the needle, and fuel screw 2 1/4 out and it runs like a champ

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  • downin

Posted November 27, 2010 - 04:35 PM


I have same bike and system except the 4.1, I have a power core 4 with mega bomb and twin air filter. I didnt get time do jet the bike or run it. Im gonna try what you did. 165 main 4th clip position and 2 3/4 out on fuel screw. Wish me luck.

  • dvn

Posted November 28, 2010 - 04:54 AM


165 main, 48 pilot and 06 needle in the stock position. Fuel screw right around 2 turns. I am running a Megabomb header with the stock muffler completely opened up w/ PMB end cap. Runs great and starts better than my buddy's EFI RMZ450!

  • bodnar44

Posted December 02, 2010 - 01:47 PM


Got my new exhaust and installed it. Thank you! I did what you said to the "T" and it runs great. I'm at 1000ft were I ride so I tweaked the mix screw a little bit different but did the 165/48 jets and needle adjustment.:thumbsup:

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