YFZ450 Jetting .

[yfzrider690]

Originally posted by SDRIDER15
MY GIRLFRIEND HAS A 2006 YFZ450 QUAD. AND IM HAVING PROBLEMS WITH GETTING IT RUNNING RIGHT. IT BACK FIRES A LOT AND WILL DIE OUT WHEN YOU PUNCH THE GAS FROM IDLE. IM GOING TO CHANGE THE JETTING TODAY AND WAS WONDERING IF I COULD GET SOME POINTERS.

*ENGINE IS STOCK
*K&N AIR FILTER WITH AIR BOX LID OFF
*STOCK PIPE WITH SPARK ARRESTER REMOVED.

I WAS GOING TO CHANGE THE JETTING TO 165 or 168 MAIN, 45 PILOT AND THE REST STOCK. WHAT DO YOU THINK THE JETTING SPECS SHOULD BE FOR THIS SET UP?

THANK YOU FOR YOUR HELP.

The jetting that you suggested should be real close. I would put the 165 in since you don't really have anything done except the K&N.

[SDRIDER15]

yeah i put the 168 and 45 pilot on last night and it was too much for it. still backfired and cut out.

ill put the 165 in and see how she runs!

thanks for the input!

[SebYfz450]

Hello everyone i got a 07 YFZ 450 Everything stock on it soon i'm going to buy a Full System HMF Competition serie exhaust and a Competition kit (Basic Jet Kit, K&N Air Filter, Outerwears) The website Recommended Jetting is 175 Keihin Hex, 48 pilot Should i stick to that? I mostly ride in trail and like 1-2 times per weeks on the track i'd like to Know what would be the best jetting for my bikes.

[cmradn213]

i have a 2008 yfz450 with a fmf powercore 4 and stainless steel mega bomb header. my air filter is a K&N with outerwears pre filter and air box lid is ON im not sure on my elevation but temperatures when i ride range from 60 to 90 degrees prolly an average of 72-75 degrees i had the dealer jet my quad before i had the k&n and mega bomb and im not sure what the jet settings are its cold here right now so its tough to tell if i need to adjust things if anyone could help it would be appreciated thanks

[trent zimmerman]

I have two yfz450's,one'04,one'05,both have HMF sport slip on's,old style,with quiet cores,velocity air filters with outerwears,EHS lid,and boyeseen quickshot 2's,HMF recomended 165 main and 48 pilot,but no needle clip position or how many turns out on air/fuel mixture screw,live in Thurmont Maryland,elevation 518',but my son races in the East Coast XC series in West Virginia,where the track elevations range from 960' in Morgantown Wv to 1930' feet in Elkins Wv.Any help,recomendations,guidence etc.would be greatly appreciated,thanks in advance.

[minerva]

Hey guys i need some help, i have a 2005 yfz stock engine with dynojet main 128 pilotjet 48 4th clip on the needle, quickshot, prodesign, kn filter and kn power lid, pro-circuit slip on, 2/15 on the air fuel screw but my bike still bogs, could it be the leak jet? What is the stock size and what size should i buy? Thanks

[ApexJoey]

New to this site and this is the best yfz450 jetting thread I found. Need some serious help with mine. It's back firing a lot on deceleration, even when letting go of the throttle after revving a little in neutral, and bogging out at 3/4 to WOT when riding. It doesn't fall flat on its face but it bogs down a bit before it catches. Cold starts with it aren't the best either, it takes awhile and gets to the point where it drains my battery out after 4 or 5 cold starts. I'm hoping its a jetting issue and any help would be much appreciated.

Sparks Racing full Exhaust
K&N air filter with lid off
Im in Long Island Ny and its around 30-40 degrees right now

i haven't opened up the carbeurator yet so I don't know what sizes are in there.