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'05 YFZ Jetting

2911 Views 6 Replies 6 Participants Last post by  mx333
Okay so my buddy and i are jetting his yfz and its very unresponsive on the bottom. it bogs very badly when you punch the throttle. We have a 168 main jet, a 45 pilot jet, and the NCVQ needle is on the 2nd notch from the bottom. he bought this used so we havent messed with it much yet, and it runs great in the midrange up so idk what the problem is with the bottom end. Oh and we live at about 3200ft. Help asap! thanks
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Okay so my buddy and i are jetting his yfz and its very unresponsive on the bottom. it bogs very badly when you punch the throttle. We have a 168 main jet, a 45 pilot jet, and the NCVQ needle is on the 2nd notch from the bottom. he bought this used so we havent messed with it much yet, and it runs great in the midrange up so idk what the problem is with the bottom end. Oh and we live at about 3200ft. Help asap! thanks[/b]

dont reall know but a 168 sounds too big for the 39mm fcr that the stock yfz has try maybe a 150 main
168 is what I run in both of my yfz's at sea level, but the bog when you stab the throttle from idle probably isn't related to the main jet. You need to be looking at the leak jet and the accelerator pump circuit. Really that is a problem with ALL FCR carbs. You might check out the forums on www.thumpertalk.com they have some excelent stuff on there about tuning the FCR.
Well first is the bike completely stock?
Are you running the lid on or off.
What is the fuel screw set at?
Baffle in or out?
Need more details.

Also if you bought it used I would recommend checking valve clearance and timing. See if the cammod was done or not.

The bog is common when stabbing the throttle off idle.

What different settings have you tried? Generally I think people run the needle clip in the middle 3rd or 4th from the top. You can try adjusting the fuel screw, or different jets. Also if you search yfzcentral.com for the word bog in the engine section, there is more ideas of what to try with the AP shot. Also you will need richer jetting running the ncvq needle, versus stock needle.

It states in the manual 158m for a stock bike/ not sure about sea level height. You could try calling a local dealer if it is stock and ask them where your jetting should be, and go from there.

I run a 168m at sea level with the mods listed in my sig. Hope this helps.
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sorry it has some mods done to it. hmf full system, boyesen qs2, open airbox, gytr filter w/ outerwear, fuel screw is 1-1/2 to 2 turns out and i think thats it............
sorry it has some mods done to it. hmf full system, boyesen qs2, open airbox, gytr filter w/ outerwear, fuel screw is 1-1/2 to 2 turns out and i think thats it............[/b]
I would leave the 168 main, 45-48 PJ. Needle on 2nd clip from top. 55 leak jet. Adjust fuel screw to the highest smooth idle. (This will need readjusted if a PJ change is made) then set idle to your liking with idle screw. Leak jet is prolly the main cause of the bog.
i would try either a 40 or 45 leak jet
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