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before you re-jet again get some 110 octane and mix it about 40/60 with 91 octane.

I dont think that cali 91 octane is enough for a un-corked YFZ. I was having problems like you ... just idling in my driveway if i gave it some throttle it would sputter real bad in the mid range. I tried all kinds of things ... jet up, jet down the red needle etc ... finally i picked up some 110 after Barely Legal said his YFZ was detonating on this chity 91 octane here. it was a night and day difference!!! took care of any sputter and ran like a top :D

Your MJ is a little too fat, especially with the blue needle
 

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id still give it a try ... it cleared up my issues.

110 here costs $4.50/gallon

mine runs great with no sputter

110/91 octane mix 60/40
hmf slip-on
alba k&n
cam-mod

45 pilot
2 turns out
3rd clip on blue needle
170 main
 

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I think your main is a little rich but hey I know nothing.

Try a 170-175
 

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Originally posted by YFZCentral@Dec 14 2003, 07:05 PM
Mods done to bike:

HMF full pipe
CFM airbox with UNI airfilter


Im running  JD blue needle #3 180m 45p 2.5 turns mixture screw and im at sea level.....any ideas? thx! 8)
backfiring is a sign of your quad being lean. sputtering is a sign of being rich. which one is your quad doing?
 

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i copied this from one of my posts at z400central about the fcr40 ... it still applies to the FCR39 though

remember that with the FCR you are controlling the slide with the thottle cable and when you whip it from idle to WOT it will bog. Call James Dean or look for his posts around the net and he will say whatever you do it is not possible to eliminate the bog on a pumper carb.

you can snap the throttle open on the stock CV carb because the slide is actuated by vaccum and wont cause that bog. but it also revs alot slower and doesnt have the same performance of the FCR.

hold it a touch above idle and then pin it WOT and it will be perfect. the bog will never effect while riding or even at launch, just in your driveway ;)
 

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Originally posted by schwendi@Dec 15 2003, 08:12 PM
i copied this from one of my posts at z400central about the fcr40 ... it still applies to the FCR39 though

remember that with the FCR you are controlling the slide with the thottle cable and when you whip it from idle to WOT it will bog. Call James Dean or look for his posts around the net and he will say whatever you do it is not possible to eliminate the bog on a pumper carb.

you can snap the throttle open on the stock CV carb because the slide is actuated by vaccum and wont cause that bog. but it also revs alot slower and doesnt have the same performance of the FCR.

hold it a touch above idle and then pin it WOT and it will be perfect. the bog will never effect while riding or even at launch, just in your driveway  ;)
Exactly right.

This condition is almost unable to be fixed with this kind of carb.

Damn, gotta give up something for all the performance.

If your only problem is when you stab it right off idle then you don't have a problem.

But I still think your main is a little too rich. But like I said I know nothing, I just got through making some 200-300 main jets :O, and getting 60/70/and 80 pilots, wonder what those could be for :uhoh muhahahahahah
 
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