YFZ Central banner

To Anyone With Aftermarket Exhaust...

187700 Views 358 Replies 291 Participants Last post by  GASoline71
Maybe we should start a compilation of jetting specs according to exhaust type, mods. and location...might give other members a place to start when modifying their bikes. Just a thought...I'll list mine soon as I get home from work and figure out what they are, exactly.
  • Like
Reactions: 1
341 - 359 of 359 Posts
Here at sea level (Long Island NY), I have the HMF Comp-Series slip on, Lid off with K&N air filter/Modquad adapter. Jets that worked perfect for me are: 168 main jet, 45 pilot, NCVQ needle clip#2. No backfire or sputter on accel/decel and pulls hard through the gears (Thanks Terse! Man knows his ishhh!)
Big gun slip on only

up one size on the pilot and main, and one quarter turn out on the a/f screw, running perfect

main is 155
pilot is 50
Full gytr exhaust
Stage one hot cam
High compression wiesco 12.1 piston
Uni air filter lid off
700ft above sea level

Mechanic put it back to stock jetting.
I think 170
I do need a new stator. Do you think this might be why the jetting is so low? He said the spark is breaking up in low rpm.
Hmf Comp Slip on, K&N filter. Stock jetting, Runs like a champ. adjusted the carb screw slightly. 1500Ft above sea level. and sometimes sea level at the dunes.
2008 YFZ450 @ sea level and warm atmosphere

HMF slip on
Quickshot 2
Cam Mod
Zip-tie Mod
Stock Intake w/lid off

Took a bit to dial this in right (with the help of you guys!! Thanks!):
48 pilot
165 main
40 leak
NCVQ needle at 3rd clip
air/fuel screw at 2 turns out

The Quickshot and zip mod probably got rid of the bog the most.....I started at 45 pilot but it idled high once it got hot and backfired on decel.....after being told to go up to 48 I did and BINGO! I FREAKING LOVE THIS QUAD NOW!!!

Still has a SMIDGE of backfire.....but don't know how much closer I can get without messing it up
See less See more
My Elevation is 6000. The jets that worked for me with a new stock air filter, lid removed and Lexx Mx slip on pipe was 45 pilot, 155 main and AFR 3.25 out. Stock needle on notch 4. MAKE SURE the plate on the slide is on correctly. The guy who was doing the work for me kept putting it on backwards so it would always be lean no matter how fat we jetted it. the guy at the local shop said he sees that all the time.
05 yfz 450
-stock engine
-a dozen or so holes in the air box llid
-fmf powerbomb header and hmf slip on
-moose foam filter
--carb settings for 30-40 degrees temp, 900ft? elev.:
-jd jet kit
4th clip on needle that came in the kit
36 main
45 pilot
-R&D remote air fuel screw set at 2 1/4 turns

..going to do the spark plug test tomorrow since its gonna be 20+/- degrees untill end of febuary. i expect to go up to a 38 main and 1 3/4 a/f mix... maybe haha
How do the holes in the lid of the air box help, like is it noticeable ?
Im a new member to the forum but have been lurking for a while

2007 yfz450
full curtis sparks exhaust with spark arrestor and fmf 4 stroke packing (header wrapped with DEI heat wrap)
quickshot 2
K&N air filter with lid on (switching to Uni real soon)
165 main
48 pilot
90 (im guessing this is my leak jet?)
elevation is 400 ft here on Long Island

Im having a serious issue, I think the signs are telling me that it's super lean but i don't know how to tackle the issue. Starts right up but then after 5 sec the rpms shoot way up without me touching anything and the idle stays high unless i pull the choke and it shoots back down to just about normal. The header get super cherry red (can see the redness through the header wrap) but i read this is normal. it also backfires here and there letting off the throttle or after shutting her off. Today i noticed blue smoke coming out the exhaust when i rev it and let off the throttle. ANY ADVICE IS APPRECIATED
See less See more
13:1 wiseco
Curtis sparks megaphone
velocity intake set up
stage 3 hotcams
+1mm valves with portwork

162 main jet
45 pilot
1 and 1/2 turns out
NCVQ needle 2nd clip from bottom
No lag in stabbing the throttle from idle
See less See more
Hey Guys
Was on here before and asked about the ecm for a 2016. I put a big gun slip on the Quad and took the lid off air filter. Ordering a K&N filter to let more air in also. Right now it does back fire but not as much as with the lid on. Stock filter still on. Maybe the oil is too thick on filter ? Haven't ridden much(1hr ) and haven't cleaned or re oiled. Will the K&N filter fix this or what is the ecm I can get to fix this back firing ? Thanks
i have a 09 yfz with:
Full dasa exhaust
Fci intake
Ported polished head
Stage 3 hot cams
478 big bore kit
I have no idea where to start with the jetting. Any help will be appreciated. Thanks in advance
Some good information in here I need to check my jetting I just got my bike and it seems to have a lot of bog

Sent from my iPhone using Tapatalk
3 angle valve job, ported head Dr d exhaust oversized modified k&n air filter, cam mod gytr high compression piston Ricky DC high output stator, 110 octane/93 octane 50/50 in Florida I'd assume Sea level 50 pilot 1 and 1/2 turns out 185 main 4th clip runs great pounds through every gear
05 YFZ 450 SE:
K&N filter
Full DASA shorty
Zip tie mod
Cam Mod
192 main
55 pilot
6th needle clip position
Elevation: 3400
Runs flawlessly..
See less See more
QUOTE (ketchupYFZ450 @ Aug 30 2004, 07:20 PM) index.php?act=fi
QUOTE (ketchupYFZ450 @ Aug 30 2004, 07:20 PM) index.php?act=findpost&pid=110909
i need specs for lrd pro 4 jet specs yfz 450
i need specs for lrd pro 4 jet specs yfz 450
06 YFZ450
Sea Level
168 Main
48 Pilot
R & D screw - 3 turns out
ProDesign intake and filter
No lid
NCVQ needle - 4th clip
HMF competition exhaust
Wiseco 12.4:1
Hot Cams stg 1
Mild Port
RM Stator
Clutch mod, zip tie mod
Rocket Ron suspension
Obor advents
93 pump gas
See less See more
New guy here and just got my '08 YFZ450 with an Athena 480 kit on it dialed in. It was a mess from the prior owner.

Sitting at sea level in Puget Sound in Washington State.

Athena 480 Big Bore Kit
Yoshimura RS-2 full exhaust
Air box lid off
K&N air filter with an Outerwears pre-filter
main Jet 180
Pilot jet 48
NCVQ needle on 5th clip
3 turns out on the screw
zip tie mod
Boyesen QS3

This thing runs like a scolded dog! It's taken me a while to get it dialed in, but finally nailed it.

See less See more
341 - 359 of 359 Posts