Strange Noise: 06 YZ450F

i've never posted here (at least i don't remember doing so), but since this is "thumper talk", thought i'd ask my question here.

my bike is not stock, and unfortunately, i've done all the maintenance on it myself. it was not running right stock (lots of back firing when i'd chop the throttle) so i changed some things. however, every time i fix one problem, it seems a new one arises. that's why i'm looking for some advice on here.


twin air filter cage (with no screen)

twin air filter

boyesen quickshot

zip ty racing pilot screw

VP 110 race fuel (straight): is this bad?


pilot jet: went from stock (42) to 45.

pilot screw: went from stock (2 1/2 turns out) to about 2 1/4.

idle: had to turn it way up to get the bike to start after all the changes.


as previously stated, the original problem was excessive backfiring when i'd chop the throttle. the air filter and filter cage did not change anything performance wise.

then, i did the quick shot and the pilot screw. being able to adjust the pilot screw with the bike running (thanks to the zip ty racing pilot screw) i was able to get the bike to quit backfiring, but i had to go all the way to about 3 1/2 turns out. a reliable source said that if you go past 3 turns out, you have to go up one size (at least) on the pilot jet.

so that's what i did. i went up one size on the pilot and then adjusted the pilot screw to about 2 1/4 turns out. however, then the bike wouldn't start very easily when cold. i finally realized that it NEVER seems to need the choke anymore. if i use the choke, it simply won't start. but without it, it fires right up. also, once it's warmed up, it usually starts pretty consistently (unless i fall over or stall it).

well, i can live with the new starting procedure (i don't care about using the choke), but the last time i rode the bike, i entered a TT Race. i usually ride/race motocross so the bike rarely gets much past 1/2 throttle (but i may be being a little hard on myself here). however, on the TT track, i was basically full-throttle most of the time. that's when it happened. my worst nightmare..... i started to notice this really annoying sound coming from the engine whenever i had the throttle off.

every time i'd turn the throttle off, i'd hear this whining or whistling coming from what sounded like the head area. the bike was running great and making great power, but after each race, on the way to the pits it wanted to gallop. oh yeah, that reminds me. one other thing i had to do to get the bike to sart was to turn the idle way way up (at least i think it was "way" up). without the idle being a little fast, the bike just won't start.

once the bike would be stopped, it sounds normal at idle.

the things i am worried about include:

air leak (carb not on completely/correctly)?

jetting all jacked up (needs more changes or did i do something wrong)?

fuel octane too high?

that's all i can think of right now. i hope i didn't leave out something crucial, but i'll bet i did. i'm scared to even start my bike again until i get this figured out.

oh, one more thing. i also changed the oil just before this race and accidently put a tiny amount too much. i started it, let it warm up, and when i checked my oil, it actually started oozing out of the engine a little bit. i drained the oil until it read the correct amount, but i am also afraid that maybe by putting too much oil in the engine and running it, it screwed up something related to the oil system internally. the oil pump (does that even exist)? i don't know, i'm just going out on a limb here. :ride:

the other option, and i hope this is the case, is that the sound i heard is actually normal for the bike when ridden that hard (which i never do in mx).

any info would be much appreciated. thanks.


start with your fuel. cut it 50/50.

Change pilot out to #48 as well.

start with your fuel. cut it 50/50.

will do.

you can read my story on jetting my new 06 YZF on the jetting forum, I love the way this bike handles and the suspension, great power, but screwing around with the carb has been a nightmare... I'm almost ready to give it back...


this is almost as embarrassing as the time i mistook my tear-offs for a YZ400! my first race ever was in 98 and i was on a yz250 (2 stroke). i had never used tearoffs before so i wasn't used to the noise they make flapping in the wind. i got about a 3rd place start in my first moto at carlsbad (250 beginner) and every time i'd be off the gas going into a turn, i'd hear some dude on a four stroke RIGHT on my azz!!! i never got a glimpse of him ("never look back" rule) but i swear he was there! then, on the way to the line for the second moto, i heard that four stroke right behind. well, that's when i figured out that it was coming from my stupid tearoffs!!! hahahhahahahha. unforgettable.

now, i hear this noise coming from my engine that sound REALLY bad and i'm about to tear the engine apart and rebuild the lower end, rebuild the top end, buy a new carburetor, buy a new exhaust system, and buy new rims, when i realized something. . . . . the only thing i had changed since the last ride before the noise started was a skid plate from Works Connection.

i went riding today to test my new theory. the first moto, the bike was, in fact, making the weird noise just like it did on the TT track. i was really worried. but i had a plan.

i went back to my truck and took the skid plate off.

second moto, the noise was gone! unbelievable!!! the freakin skid plate was either vibrating and/or amplifying the noise from the engine!!! i mean, this noise is extremely annoying and impossible to get used to.

i didn't have it with me, but the next time i go to the track, i'm going to take the foam that comes with the skid plate and try it with the foam installed. i didn't use the foam because i don't care if mud gets packed in there. but maybe the foam deadens the vibration or whatever.

another rider at the track actually came up with a good analogy. it sounds like when someone runs their finger along a wine glass and it makes that annoying whining sound.

so be advised, if you bought a factory connection skid plate, make sure you use the foam. actually, i haven't tested this theory yet, but i'll let you all know what happens the next time i ride.

i'm really relieved i didn't have to do anything to the engine. who would have thought that a stupid skid plate can make the engine make a weird noise. haha. :applause:

The 06 is noisy period - foam will cut it out

get rid of the race gas you using - it is and will cause some jetting nightmares and seal damage, Run VP U4 or pump gas 93 octane..yours sounds very lean

What is your altitude the 48 pj may be too much

If it all fails - remove the quickshot and start over :applause:

thanks for the advice to everyone who helped me out. however, now that the noise is taken care of (stupid skid plate), i'm pretty happy with the jetting. the bike starts right up, has insane throttle response, and revs further than i dare to test.

oh yeah, i forgot to say, the single, most effective mod i've done to my bike (and the same goes for the 99 yz400 i used to have) is to add two teeth to the rear sprocket. i recommend that change to everyone. unless you're racing in the desert or something like that. for moto or play riding, it's the hot ticket. the bike comes out of turns WAAAAAAAAAY better with that change and will pull 3rd gear through even the slowest of turns (and with me at the controls, that's REALLY slow). :applause:

After I installed my W/C skidplate my 450 made some crazy sounds too....especially when you have your head over the triple clamps...sounds like it's knocking. Pretty annoying, but there are some rocks where I ride so I'll just have to get used to it...the stock one doesn't cover the frame rails at all.

Thats something Im going to have to check out I installed a utah aluminum skid plate on mine.I also put a cycra disc guard on at the same time. I was in a hare and hound the first ride after the installation.Halfway through I started getting a noise like my rotor was rubbing the guard. Kinda like zzzzzzzzzzzz. I checked after the race nothing rubbing. ive noticed it almost every ride, I was thinking maybe I was losing a bearing in the transmission. Ill have to check the skid plate. I also bought the Billy who oil jug best 20.00 Ive ever spent no more over fillin.

I installed a Moose Racing skid plate on my WR and could not believe the engine noise.

Ended up using some foam tape and it was gone.

I thought something was wrong...

that sounds like it's your skid plate dude. i hypothesized all the same things. i checked my front wheel/brake, and was starting to consider rebuilding the lower end when i figured it out. weird, but true.

it's about as illogical as putting some new footpegs on your bike and the engine starts making some weird noises. it's like .... &%$#@!? hahahhaa. at least i figured it out. i still haven't tested the skid plate with the foam piece installed. i just hope that takes care of the noise, cause i like the skid plate (the stockers blows), but i can't live with that noise. it's VERY irritating. :applause:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now