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i have a 2004 yfz, its running way to rich there is currently a 172 main in there with a 42 pilot, im running a biggun slip on with the air box lid on but with vents instaled. i am getting a lot of back firing and when the throttle is tapped and let out it is throwing a flame about 8 inches. im at 853ft above sea level. what should i change my jetting to?
Just from personal experience with mine- if you can remove the airbox lid. You have an aftermarket fuel screw
 

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i have a 2004 yfz, its running way to rich there is currently a 172 main in there with a 42 pilot, im running a biggun slip on with the air box lid on but with vents instaled. i am getting a lot of back firing and when the throttle is tapped and let out it is throwing a flame about 8 inches. im at 853ft above sea level. what should i change my jetting to?
Just from personal experience with mine- if you can remove the airbox lid. You have an aftermarket fuel screw
i did remove the lid and it made a huge difference, i turned the air fuel screw out a turn and a half from where it was and it seems to be a alot better, but still have a little back firing
 

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I have 2005 yfz and quite recently I moved from a Louisiana with the elevation being of 82 ft above sea level to Michigan where its 615 ft above sea level. If its possible I would like the specs with and without the breather lid and also with and without the cam mod for rejetting. I have a RS-2 yoshi slip on pipe and I`m also wondering if the GYTR re jetting kit is worth the money or should I buy something else that better matches the yoshi pipe. Sorry if there's so many questions all in one post but I have been doing lots of research and these all seem to tie together.
 

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Just rebuilt my friends motor after he broke 3 valves and Im having trouble getting the jetting right. He has a fmf slip on on it ( i believe its the titanium 4) and the specs that fmf told me over the phone are: 165M 42P 2 Turns out on the fm screw, and 3rd clip down. I just cleaned the whole carb for the 3rd time and set it all to the above specs and the bike runs only with choke on. Im guessing this is because w/o the choke its not getting enough fuel. Do you guys think that if I go with these settings "YFZ wpipe and lid on: 168m 45p #5 or #6 clip should be very close" from the first post I should be good? I wanna get this right because I think the motor blew due to incorrect jetting. He had it running very lean which would cause the valves to heat up way too much and over time break. I dont want this to happen again and so far I had no luck with jetting on this thing so I need some help. Im gonna try the new set up tomorrow and see if it helps but if anyone knows of better setting please let me know. Also I got rid of the carburetor switch and still need to readjust tps after I tore it all down to soak overnight but the yamaha manual specifies to do that last after everything has been tuned so Im not sure if i should set it to any base settings before doing more tuning. Also one more thing that I'm unsure about, when talking about the clip position on the needle do you count the grooves from the top or bottom? Thanks a lot in advance

this is on a 07 running at sea level
 

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Try 170m, 48p, 3rd and 1.5 turns out, also check for vac leaks, sounds like it might be sucking air.
 

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Hey y'all, new to this site and was hoping for a bit of jetting insight. I picked up an 08 yfz and it's had carb issues. I'm currently running a 168m, 45p, needle in 3rd clip from the top, a/f screw 2 turns out and I'm at sea level.

I have the ziptie mod done,
cam mod
k&n filter, no lid
and a... black slip on, no name on it but it's not stock.

It seems to run well when cold, but once its warmed up it stumbles a little at first then runs pretty well up to WOT. I was thinking lowering the P jet to a 42 because it runs better when it's cold. Any ideas? Thanks!
 

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2006 yfz 450

I have a 2006 yfz 450 with the cam mod, air box lid off and a big gun pipe. I bought the JD jet kit and put the 45 pilot and 175 main with the blue needle on the 3rd clip. im at about 650ft above sea level. It was back firing and shooting out flames when i would let off of half throttle so i moved the clip all the way to the bottom and it didnt stall from idle to 1/4 throttle and didnt back fire after letting off wot but would back fire when letting off half throttle so i was thinking about using the 170 main and adjusting the clip but broke the jet by over tightening it when installing it. Im just wondering if using the 170 jet will fix my problem and if i should try to buy just a 170 jet from JD without buying the whole kit or if I have other problems. Thanks for any help.
 

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I have a 2006 yfz 450 with the cam mod, air box lid off and a big gun pipe. I bought the JD jet kit and put the 45 pilot and 175 main with the blue needle on the 3rd clip. im at about 650ft above sea level. It was back firing and shooting out flames when i would let off of half throttle so i moved the clip all the way to the bottom and it didnt stall from idle to 1/4 throttle and didnt back fire after letting off wot but would back fire when letting off half throttle so i was thinking about using the 170 main and adjusting the clip but broke the jet by over tightening it when installing it. Im just wondering if using the 170 jet will fix my problem and if i should try to buy just a 170 jet from JD without buying the whole kit or if I have other problems. Thanks for any help.
It doesn't seem like too manu pople are still paying attention to this thread, but I'll help you with what I know. it seems like you're pretty rich. Flames are usually due to un burnt fuel in the exhaust. I would recommend starting at 168 main, needle on 3rd or 4th clip from the bottom, and a 45 pilot. fuel screw 2 turns out. have you done the zip tie mod? Also, does it start without the choke on?
 

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I was messing with it yesterday and got it dialed in pretty good. I left the 175 but have the needle clip 5th from the bottom and it needs the choke when cold but starts right up. But starts a little harder when hot. Everywhere I read it says that's a sign of too rich which is fine with me. I'm not sure what the zip tie mod is.
 

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Google zip tie mod, it's pretty easy, and cures some of the low end bog. You're a little rich, but better to be today than too hungry! As long as it still runs good hot. And the needle and main jet cross over. So your needle is super lean an your MJ is pretty fat, so the balance. I haven't gotten around to dropping one on my pilot yet.
 

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I just got an 05 yfz 450 a few weeks ago and I have basically built it from the ground up. It would be perfect if I could just get the carb lined out properly. It will not idle and you have to keep it in higher than normal rpm to get going or else it will cut out and die but it seems to run fine it high rpm and sometimes backfires out the exhaust. I'm thinking it is running too lean. My main jet is a 150 right now and the moose needle is on the 5th clip but I'm not sure what my pilot is. Elevation here is around 350 ft. My bike has a ported and polished head, intake, and Lexx slip on. If anyone can help me out or at least give me something I might be able to start with, I would appreciate it. I'm ready to ride this thing!
 

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OK I have a 2006 yfz in need of some jetting help. It has a 478 big bore kit I did the can mod. Zip tie mod. I have a yoshi slip on and a vortex race filter with the lid off. Any ideas where I should be ?
 

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I just got an 05 yfz 450 a few weeks ago and I have basically built it from the ground up. It would be perfect if I could just get the carb lined out properly. It will not idle and you have to keep it in higher than normal rpm to get going or else it will cut out and die but it seems to run fine it high rpm and sometimes backfires out the exhaust. I'm thinking it is running too lean. My main jet is a 150 right now and the moose needle is on the 5th clip but I'm not sure what my pilot is. Elevation here is around 350 ft. My bike has a ported and polished head, intake, and Lexx slip on. If anyone can help me out or at least give me something I might be able to start with, I would appreciate it. I'm ready to ride this thing!
Try 168-170 main, 45 pilot, needle 3rd clip and screw about 1 1/2 turns.
 

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OK I have a 2006 yfz in need of some jetting help. It has a 478 big bore kit I did the can mod. Zip tie mod. I have a yoshi slip on and a vortex race filter with the lid off. Any ideas where I should be ?
Probably same ballpark as what I posted on his except maybe a little bigger on the main, 172.
 

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Elevation 900-1100ft
weather 0-10 degrees (35-45 fahrenheit)
K&N intake lid on
Slip on GGB exhaust
main 165
pilot 45
NCVQ 4th clip
mixture screw I didn't touch

It's running a little stuttery in the mid-range, do i tweak the mixture screw or change the needle to the 3rd clip?

temps will continue to decrease, i'm in Ontario, Canada.
 

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I have a 05 yfz450 with a drd pipe and cold air intake the quad was in Idaho I trade my quad for this one I live in Michigan,and its like 50-70 degrees here now not sure of elavation difference Idk how to rejet it or what to do I mean I can change the jets don't know to go up or down the jets in it now are a 165 main and 50 pilot it runs only on choke and backfires anyone can u help??
 

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i just had my atv built and need help rejetting my yfz.
it has stage 2 hot cams, 12.5 compression cp piston, Big bore 478cc, Fat boy full exhaust at 2200 feet. any suggestions?
 

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I have a 05 with full exhaust pro flow intake and uni filter no lid head is ported with hot cams i use a oc-emr needle 3 clips from bottom 45 pilot and a 182 main and I love it
 
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