FMF PowerBomb SX header and jetting?

9 replies to this topic
  • kirkw

Posted January 05, 2004 - 02:57 PM


Already have a Q pipe, which replaced stock, and have it jetted appropriately. Installing a Powerbomb SX model header to replace stock. I did the recommended changes for the pipe, but are there any required because of the new header? Thanks in advance for anyone that has done this before. Happy New Year to all!

  • kirkw

Posted January 07, 2004 - 09:45 AM


I installed the header and now when full throttle after some acceleration it has this weird hestitation and misfiring feel. Is that the rev limiter kicking in? I have a 180 main, 2 3/4 fuel screw setting. Bottom and mid seem OK. Any ideas what the problem is???

  • LiquidSilver

Posted January 07, 2004 - 08:12 PM


In previous bikes, whenever a larger volume header was installed... I had to go WAY up on the main jet.

I did a lot of power-up work on an XR650L... cam & pipes... and I had to go off-the-charts 'up' on the main jet.

Others here have tons more knowledge about this bike than I do so far, but unless they have other ideas... try a 200 main or slightly higher. The rev limiter wouldn't be in a different range than before.

Didn't FMF promise a jet kit to be included with that pipe?

  • kirkw

Posted January 08, 2004 - 10:15 AM


Liquid, I think that the jetting kit only comes with the complete one piece header&pipe system for the Titanium 4, not the two piece Powerbomb and Q. In any event, I had gone from a main 168 to 180 when I did the pipe, do you think the header would lean it that much more???

  • kirkw

Posted January 08, 2004 - 05:34 PM



Tried the mainjet. Went from the 180 to 190 and then 195 and up to 3 screws out on fuel screw. Sounds and pulls better low, but still an odd hiccuping or hesitation under acceleration from about 1/2 to full throttle, especially noticable at full throttle. No real popping or backfiring. The gas is about 75 days old. Think that could be it???

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  • The_Blue_One

Posted January 08, 2004 - 07:43 PM



I'm by no means a jetting expert but you may be to rich on the main causing the hesitation.

I just got the mx power bomb and went up 1 on the main. and 1/2 a turn on the fuel screw.

Try posting in the jetting forum and JD will lead you in the right direction :)

  • TonyDeCoster

Posted January 08, 2004 - 08:37 PM


You shouldn't have to rejet for the header. FMF's website recommends the stock 45 pilot, a 180 MJ and 2 3/4 turns out on the fuel screw

  • R_Little

Posted January 09, 2004 - 07:23 AM


I think yoi are rich. My 200 WR was doing the same thing lately.I leaned the main jet from a 168 to a 162 and raised my DRQ needle from 4 to 3. Runs great now.

That 180 main seems very rich to me, header or no header.


  • Bill

Posted January 10, 2004 - 03:03 PM



Change to YZ timing and try the jetting in my signature. Or order the JD kit. Someone correct me if I'm wrong but, the JD kit will provide a speadsheet for making changes at every throttle setting ie if you chage the main you should try ___ pilot at ___ needle.


  • kirkw

Posted January 12, 2004 - 01:14 PM


Thanks for all of the input and help. In a nut shell, the problem turned out to be bad gas and a bone head at the throttle :). Since I do not usually test on a long enough paved straight away and prefer short shifting, I never hit the rev limiter before. So the final was as suggested on FMF's site, 180 Main, 3rd position on the stock clip and 2 3/4 turns out. Throttle wheelies in 2nd and 3rd no problem. Will find out what happens in 4th and 5th when I get enough space :D


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