Jetting - YFZ450

Hi all,

I know this forum is mostly bikes but gets a lot more action that ATV Talk and the YFZ is very similar to the YZ. I took the quad out for the first time this weekend since doing all the modifications and it seems pretty good down low - mid range. I'm not sure if its rich or lean up top, but the weather was pretty crappy today as well.

I have a 2006 YFZ450 - stock bottom end.

-2007 MMAD ported head - stock valve train

-MMAD stock bore piston - 14:1 or so compression

-Web +5 cams

-FCI intake

-42mm FCR carb

-DASA pipe

My elevation is right around 700 ft. above sea level.

Right now I am running a 195 main, 45 pilot. NCVQ needle on 4th clip. Carb also has R&D Power Bowl with the adjustable leak jet. Think I'm set around a #40 right now.

Any help/suggestions would be greatly appreciated!


what is the running issue you are trying to cure?

My guess is that it has to be with the main jet because it kinda stutters 3/4 throttle and past. I figured this was being very rich but not positive because the brand new stainless pipe has already discolored a lot on the header pipe? I've had stainless exhausts on buggy's and never had them discolor this bad, this fast! Also, not much "soot" on the muffler, so has me questioning myself whether I am very rich or very lean? Thanks in advance!

Had the chance to take it out again Saturday. Acts as if it is hitting the rev limiter at WOT. That would be cause I am too rich, correct?

Anyone? :doh:

sounds too rich to me.

Yep, your are running too rich on the main. it will bog like your running out of gas if it's too lean at WOT.

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