I just bought a 450.  I was told the baffles were taken out of the exhaust, andit is jetted(who knows to what).  Thats all the "engine" mods that are done.  Supposedly.  The problem is, while riding at high rpm if I just drop off the throttle completely the thing backfires between 1 to 3 times.  Also, when coming to a stop it seems to just die almost everytime unless I keep on it.  Then after this happens, it is almost impossible to start.  I dont know if there is another thread like this one somewhere else.  This is my first day with the quad and my first time on this site.  Any help would be greatly appreciated because I would like to try and go riding in the morning.  Oh.  Its an '06 and the dealer cant get to it till monday if you were wondering.  

ok, if it's been jetted and the baffles are out.


with just the baffles out it should have less backpressure causing a little more fuel to enter into the cylinder. less so with a 4 cycle, but still a little more fuel.

if they jetted it then most likely they jetted it larger. (normally the case)

you should have a fuel/air mixture screw on the side of the carb... not the idle adjustment.

if you turn it to the left you get more air, if you turn it to the right you get more fuel into the mixture.

first things first.

remove the air filter, crank it up and ride a few minutes, see if it has the same problem or if it gets worse.
if it gets worse then it's getting too much air
if it gets better then it is getting too much fuel in the mix.

without the air filter in it will draw in a little more air.
if it gets worse or stays the same.

mark where the air/fuel mixture screw is now, then in 1/2 turn increments turn the screw to the right.
(turn it one half turn ride it for 3 minutes see if it gets better, if not then turn another half turn to the right.  keep up with how many half turns to the left or right you took it from where it was already.)


if no change or it gets worse take the screw back to where it was before you started and try it the other way.

you may have to rejet it. especially not knowing what they jetted it to. some people will overjet thinking bigger jets means more horsepower. well it only means more horsepower if you aren't going overboard, and as long as you tune your carb in right.

if it bogs at top end it's too rich if it cuts out at top end it's too lean.  

Now I am not really sure which is the air/fuel mixture screw.  Is it the red screw on the bottom of the carb with the numbers on it?  I have no clue and I cant seem to find any pics or diagrams that say it.  

yes, 450 put em on the bottom.

the 450 used to be basically change the exhaust, rejet the carb and throw the air box cover away and you were race ready, so i think they designed them to do this again only you have alot of problems if you don't do this.

i have had 5 or 6 yzf 450's come through my shop for this problem.
it's always a matter of rejetting and tuning the carb.
while scratching my head and getting frustrated and eventually getting it tuned in.  and none of them tune the same.

overall they are awsome quads and dirt bikes once you get em tuned in.  

i hear if u take the baffle out it loses bottom end and i dont now a bout the back fireing my dads z-400 does that and if u come to a stop it just shuts off and its hell trying to start mayby u should try to change the jet sizes  

Ill tell you what wolf1.  You know your stuff.  I turned the fuel/air screw all the way in and came out about 2.5 turns and the 450 is running 100 times better.  I think a little more tuning and it will be running top notch.  Thank you very much for your time and help.  

yeah sometimes you get it the first time around, other times you have turn it this way, until you get it too far, then come back the other way.  kind of like a combination lock, until you get it just right.

you still may need to fine tune it a bit. just see if it falls flat at top end or cuts out.
if you need more help let me know i'd be glad to help you get it tuned in right.
owning a bike repair shop is the greatest job i have ever had!

Glad to help!!  

Wolf1, can I pick your brains a little?    I am having exactly this same issue.

I have an 05 YFZ that I just purchased.   It has an HMF pipe, with the airbox lid off, and K&N style filter.  I also has and HMF Jet kit.   These are the only mods.

The HMF Jet kit that is in it has a 180 main, and a 45 pilot.   The needle is the stock needle on #4.  Fuel screw is 2 1/2 turns out.

When I ride, it tends to bog down in the corners at low RPM, and then it will die.   It will not restart until the engine is cold again.  It also has some lean pops on deceleration.

My gut feel is that the main is way rich, and the pilot is lean.    I think it should be about a 172 main, and a 48 pilot... also maybe another clip richer on the needle.

I am at 900 feet elevation.  

Any thoughts would be greatly appreciated.  Thanks in advance.  

well it does sound rich at the main.
and if the pilot is lean then the vaccuum from the cylinder will cause the gas to splatter as it comes past the needle trying to draw in the amount of fuel it needs.
causing you to fall out of the powerband.

do you still have your factory jets?
if so install the factory main and leave in the 45 pilot. see if that doesn't straighten it out for ya.

I do have a question though, when you put the jet kit and exhaust on did it idle at all when you first tried to start it?

if it didn't idle and you had to adjust it, then your needle most likely will be fine.
but if it idled high when you first started it after the jet kit install then your needle is probably too small.

if you end up rich at the main and lean at the pilot and your needle is undersized then it becomes pretty impossible to tune it in. you can adjust it to idle but it falls flat while riding.

throw the airbox lid back on and it might help you get it tuned in faster, then you can remove the airbox lid and turn the fuel/air mixture screw in about 1/4 - 1/2 turn. just depending on your machine.  

Thanks Wolf.  

The jet kit and exhaust were actually on the bike when I bought it, so I am not sure about how it ran after the change.   I don't have the airbox lid either, as it was off when I bought it as well.

Do you think there is any advantage to switching to the YZF needle?   I think its the NCVQ?

Where is your shop at?  Maybe I will just drop it off! :-)  

you are in the chattanooga area?

geeze yeah bring it on by.

maybe we can tune it in right for ya without having to change anything.

bring it by, no labor just any parts you may need.
and you probably wont need much. but I certainly wont know until I can look at it.
i'll be out today until late.

but you can drop it off, probably thursday would be the best day for it.  

No, I am not in the Chatanooga area.   I am in Indiana.   Dang.    Thats why I was asking, because I didn't know where you were located.   I would bring it a couple hours, but Chatanooga is a little far.   I will keep screwing with it, and I will hit the right combo eventually.

Thank you for your advice.   I wish you were closer.  I can't find a shop around here that has a clue how to tune.   Everybody is just willing to install a jet kit for you out of the box.  

yeah it sucks at most shops, they want to install a jet kit so they can charge you for it and make more money.
few shops will actually tune one without a jet kit.
or a warranty.

sorry i thought you were in my area. keep the pm's and posts coming eventually we'll get it dialed in.
i'll look around here and see if i have some factory jets for a 450,  if so i'd be happy to send them to you.  

Hi wolf1!  

It seems like you got a few experiences in jetting!  Thats awesome.  Its hard to find someone that will help others out. My hats off to you.

I have never ran into this problem but I have heard of others running into but yet to hear a similar answer.

YZF 450 04' White bro's exaust, K&N, No air box.  
After the machine is warmed up and you come to a stop it idles high (like your holding the throttle a 1/4 way down)
If you let out the clutch just enough to engage it and enough to lower the rpms, and then pull in the clutch it idles fine.

(My idea is it is running lean)  

Got any ideas??  

hey i have a 07....mine never did this put uf u were pinned and puled the clutch in it would stall...or it would hit a dead spot and sputter.....but i asked a dealer and he told me to leave the lights on at all times...this problem went away...btu i think u need to check the jetting and that should solve the problem