FMF Full Exhaust /Jetting help 2008 yz 450


6 replies to this topic
  • cacimx622

Posted December 09, 2007 - 01:28 PM

#1

Hi folks, I just traded the yellow bike No fuel Injection for me yet!!!! in for Big Blue 08 yz 4 fitty and am super happy.

I just put a FM Mega Bomb Header and a Power Core I could'nt swing the other 70 buck's bad time of the year if ya no what Im saying anyway's,


My questions is I took it for a spin the other night for about 15 min and she was really popping on Deceleration however it was only 32 or 33 degrees out could this have had something to do with it?:busted:

I have the stock jet's in it not even sure what they are.Can someone tell me what is the best jetting set up for this application.

I also went up 1 tooth on the rear much better IMIO.


Sorry have'nt had time to change my Avatar.

Happy Hollidays thanx.:banghead:

  • JakeSchmutz108

Posted December 09, 2007 - 01:49 PM

#2

when its that cold out its a little hard to jet it. it will run rich when its cold. so you need to lean the main out i ran a 185 main in my 250f in the summer and about 2 jet sizes smaller in the winter. that should help with your backfireing in decel.

  • todds924

Posted December 09, 2007 - 01:58 PM

#3

Hi folks, I just traded the yellow bike No fuel Injection for me yet!!!! in for Big Blue 08 yz 4 fitty and am super happy.

I just put a FM Mega Bomb Header and a Power Core I could'nt swing the other 70 buck's bad time of the year if ya no what Im saying anyway's,


My questions is I took it for a spin the other night for about 15 min and she was really popping on Deceleration however it was only 32 or 33 degrees out could this have had something to do with it?:busted:

I have the stock jet's in it not even sure what they are.Can someone tell me what is the best jetting set up for this application.

I also went up 1 tooth on the rear much better IMIO.


Sorry have'nt had time to change my Avatar.

Happy Hollidays thanx.:banghead:


Stock jetting is not going to be that far off for your setup. Try turning your fuel screw out to 2 1/2 turns. That should take care of the excessive popping. If you need to go any more than that you need a 48 pilot. I would think that because of the temperature, the stock jetting is going to be really really close. Try the fuel screw first.

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  • grayracer513

Posted December 09, 2007 - 02:34 PM

#4

when its that cold out its a little hard to jet it. it will run rich when its cold. so you need to lean the main out i ran a 185 main in my 250f in the summer and about 2 jet sizes smaller in the winter. that should help with your backfireing in decel.

Totally backwards.

Colder weather requires richer jetting, not leaner.

  • kiwiinsd

Posted December 09, 2007 - 03:07 PM

#5

My opinion / DRD , Doug Dubach exhaust best match for Yamaha
Make sure all connections etc tight , a leaking head pipe can cause popping,
do you recall REED's bike at Milleville a couple of years ago ?
Of course , if all is well here then re - jetting will help .

  • adamdf

Posted December 09, 2007 - 03:41 PM

#6

Totally backwards.

Colder weather requires richer jetting, not leaner.


You said it! That one had me scrathing my head too.

  • cacimx622

Posted December 09, 2007 - 04:00 PM

#7

Love the way the bike turns it just as good as my 06 RMZ I just sold.

The shorty it came with did rob it of a few ponies I agree.

The 49 tooth had to go as well. Go team Yamaha!!!!! Go Broc Helper it's your year this year.:banghead:





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