carb problems


7 replies to this topic
  • bigdaub

Posted August 26, 2007 - 03:42 PM

#1

Just put a new fmf powercore 4 on my 07 yz450 + now the bike runs a little rough, and backfires like crazy on decel - what do i have to do to fix this? and does anyone know what the stock setting is for the air screw?

thanks!

  • WB450

Posted August 26, 2007 - 04:12 PM

#2

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  • Ga426owner

Posted August 26, 2007 - 04:14 PM

#3

Just put a new fmf powercore 4 on my 07 yz450 + now the bike runs a little rough, and backfires like crazy on decel - what do i have to do to fix this? and does anyone know what the stock setting is for the air screw?

thanks!


it needs to be rejetted for the pipe and fuel screw adj correctly.....
stock FS adj is pre set from factory.....in order to get your preset you must count the # of turns to full in and record this......usually ranges 1.5-2.2 turns out, before any adj is made:thumbsup:

  • Jekel

Posted August 26, 2007 - 07:46 PM

#4

Also re-check your instal for any leaks. FMF should provide you with recommended jetting changes.

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  • bigdaub

Posted August 27, 2007 - 05:09 PM

#5

well i pulled apart the carb today, got my 48 pilot jet in, and then noticed that my pilot screw was GONE nowhere to be found! has anyone else had theirs fall out? Im very surprised the bike ran at all without it.

  • WB450

Posted August 27, 2007 - 06:16 PM

#6

well i pulled apart the carb today, got my 48 pilot jet in, and then noticed that my pilot screw was GONE nowhere to be found! has anyone else had theirs fall out? Im very surprised the bike ran at all without it.



Yes, it sure runs like s$%#, follow the #3 I think with the new one and you should be good.

  • maddogyz250f

Posted September 25, 2007 - 12:34 PM

#7

well i pulled apart the carb today, got my 48 pilot jet in, and then noticed that my pilot screw was GONE nowhere to be found! has anyone else had theirs fall out? Im very surprised the bike ran at all without it.


I have had an aftermarket screw fall out on a CRF450R but never the stock one.

  • grayracer513

Posted September 25, 2007 - 02:42 PM

#8

People back out the screw too far to compensate for an undersized pilot (or to devote too much energy to eliminating decel popping) and end up with too little spring tension to hold the screw in.





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