well for one thing its NOT running lean its running way to rich i have tried taking the airbox lid off and with the air screw out more and it doesnt help and i have ordered dyno jet and its totally opposite than fmf dyno jet told me to use a 134MJ when stock wuz 158 and the jet is 2 separate peices the adapter and the jet and doesnt dropping the needle down a clip let more fuel in?

 

Well according to your first post, shooting flames and popping on decelaration is a very good sign that you are lean. Does your header glow red when you are riding? I can almost guarantee you, that you are lean.

Second of all, the yfz450 doesn't have valves to adjust, it uses shims...
third, you are right, the jets that come with the factory 4 use an adapter, and that's why you can get inconsistant results with the jetting.

You could lower the clip on the needle and that would make you more rich but it would kick in until you hit about 3/4 throttle.

Believe me, you are running to lean, I know because I spent many hours working on my jetting on that system.

 

spark plugs dont lie and if i was runnin lean they would be white but they are blacker than hell so it is runnin rich and yes it does glow red at night time. o yea and i said the jets from dyno jet came with an adapter not FMF

 

One more time for those in the cheap seats....45 pilot, 168 main, 5th clip on stock needle. Remove airbox lid. These numbers are for the Keihin jets. So you can go and get these jets and get your bike dialed in or you can continue to argue with people cause you dont have the right jets. Good luck.

 

Ok, go ahead, go leaner then, melt your engine. What do I care....
and FMF's Jet kit that comes with the factory 4, IS a dynojet kit

 

I live in the same elovation range as you and i put dr.d pipe on k&n filter cut the screen and cone out air box lid off.The best jetting results useing dyno jet kit 48pilot 160 main jet 5 groovesdown needle and 1.5turns mixture screw

 

Ok, go ahead, go leaner then, melt your engine. What do I care....
and FMF's Jet kit that comes with the factory 4, IS a dynojet kit

well im just tellin u that it is not runnin lean let me ask u a question is a black spark plug mean its runnin lean????? answer that before u answer my jet question and if the FMF jet wuz dyno jet i think it would be the same as the dyno jets but it aint i have ordered the power kit stage 1 and 2 for my bike ik wut the dyno jet is and wut it isnt, not to mention ur runnin the full system im only runnin a slip on so the jetting shouldnt be the same as yours

 

I don't know how black your spark plug is, but a healthy spark plug is suppose to be tannish/brown. If it is like midnight black, then yes, that is a SIGN that you are running rich.

Maybe you were running rich at one point? The stock yfz450 configuration is one of the most stuffed up setup's ever. Even if you don't have any mods on your quad, and its barebone stock, you can still be rich yah know?

If your elevation is really high, or if where you live is very humid, you can run rich straight off the showroom floor, WITHOUT ANY MODS. But then again, I don't know when you last changed your sparq plug.

However, your description of a glowing pipe, popping on decelaration, backfiring, those are all signs of a lean setup. Like I said, do what you want, but I think you are running lean.

Also, I shouldn't have said that the FMF kit IS a dynojet kit, what I should have said is that, FMF's kit is made by dynojet and is re-labled as a POWER UP kit. Go ahead and call up FMF and find out for yourself, they will say the same thing, I know because when I was jetting my quad that's exactly what they told me. I had to call Dynojet to figure out what the hell is up with their jet kit.

 

Is the 168 main a dynojet? Their numbering system is totally different from stock kehin jets. Also, like someone said...maybe you were rich at one point. They recommend a new plug
when you're doing the plug test. A 162 main sounds way lean to me. If that pipe is glowing red, you're certainly lean. Try daddogs jetting page for some useful information. Also, buy yourself a handful or $3 jets and try different combinations. Write down all the combos and what the bike is doing with them. Also, get the ncvq needle...It's about $13 from the dealer. You have to ask for the needle for the yf450, a dirtbike. My dealer parts guy was an idiot and had no idea what ncvq was. I about had to beat him over the head with a bat to get him to order the needle for my yfz.

 

ok this is ganna be my last post on this subject it is not humid where i live and i do not have a high elevation i got a FMF slip on muffler and i changed my spark plug about 3 times on adjusting the carburator all were black (idk wut is was stock b/c i never changed it after the pipe) but i changed it 2 other times and it wuz midnight black as u would say, so ik im not running lean i cant be, another thing how would u go and say running it to lean would meltdown my motor when its a 4 stroke and there is oil already in the cylinder not like a 2 stroke where the oil and gas are mixed? i was just wondering