EXC 450, what is this Sound from intake / throttle ???

[Michael Back]

I have an EXC 450 from 2006 and recently I noted that it has a strange sound from the carb / throttle at idle.

Take a look at this video:

http://www.youtube.com/watch?v=YThaKn4MaVg

It's like the throttle is making a ticking sound at idle. The same sound as when you let go of the throttle / handle, just at every rev.

It disappears when the RPM is increased slightly.

Any ideas ????

Thanks in advance.

Michael.

[rufus]

One possibility.
ADC (automatic decompressor) spring is worn out and lettting the ADC rattle back and forth at low rpm. KTM says that the idle should be set at 1800 rpm. 1800 is too high for me though.

OR.........cam chain tensioner is worn out. The notches/auto adjust section can get stripped. It is easy to check, 2 screws and pull it out.

If the tensioner is fine and it is bottomed out ( no adjustment left)then your cam chain could be worn out.

[clapped_r6]

post it at ktmtalk in the rfs section, you will probably get a definitive answer quickly.

[Michael Back]

Thanks for the replies.

I´m quite positive that this sound is from the intake and not the engine casing. Its like the vacuum causes the throttle to close with a quick "click" at every stroke...

Can the throttle somehow be worn ?

[Jacl-Kampuchea]

Idle too low and de-comp making the rattle, I'd say.

But look into the advice offered above also, as I'm only half a mechanic and only half a car mechanic at that.

My 450 is the same year, I increased the idle and the noise went away.

Looking at your video made me think I REALLY need a new air filter too!

[Michael Back]

Originally Posted by Jacl-Kampuchea

Idle too low and de-comp making the rattle, I'd say.

But look into the advice offered above also, as I'm only half a mechanic and only half a car mechanic at that.

My 450 is the same year, I increased the idle and the noise went away.

Looking at your video made me think I REALLY need a new air filter too!

Thanks for the input... I´ll look into this...

By the way, the air filter is brand new and havent run for one singe hour yet...

[Michael Back]

Originally Posted by lesjive

Yes it can. There's a rubber ring(22) between the slide(19) and the backing plate(21) that wears out, causing chatter.
Make sure you put the backing plate right side up when you re-install it.
Also check the wheels(20) for play.
Check inside the carb body for wear. If the slide's been rattling around it can cause grooves.
I replayed your vid, and it does kinda sound like thin metal on metal..

This sounds right !
Thank you very much for the input... ... The rattle sound clearly sounds like a thin metal plate against some other metal... I find it very likely that this is the reson...

I´m looking forward to take take the carb apart and I´ll revert with feed-back soon as possible.

Merry Christmas everyone !!

Michael.

[Steveman]

Originally Posted by lesjive

Yes it can. There's a rubber ring(22) between the slide(19) and the backing plate(21) that wears out, causing chatter.
Make sure you put the backing plate right side up when you re-install it.
Also check the wheels(20) for play.
Check inside the carb body for wear. If the slide's been rattling around it can cause grooves.
I replayed your vid, and it does kinda sound like thin metal on metal..

+1 typical slide rattle sound. I am 100% sure

[AWM]

Originally Posted by Jacl-Kampuchea

Idle too low and de-comp making the rattle, I'd say.

But look into the advice offered above also, as I'm only half a mechanic and only half a car mechanic at that.

My 450 is the same year, I increased the idle and the noise went away.

Looking at your video made me think I REALLY need a new air filter too!

That is common with RFS's.And it scares the shit out of you till you know what it is.But that bike is idle'n to fast for the de-comp to rattle off the cam.In my opinon of course.
Time'n chain adjuster is where id start.
I had a 2001 Husaberg FE400 that rattled the de-comp arm off the cam.I found the de-comp cable was snapped inside the cable,and was just bang'n around under the valve cover.
Pulled the cover and took the de-comp out,yanked the cable and arm and never had a problem again,,,well no noise again.

[laramie LC4]

get that fixed or it will rattle loose and parts will break off. my 640 ate, chewed up, and spit out a corner of mine. left me stranded in the middle of the dez, didn't seem to bother the bike at all. once replaced it fired back up and ran. on later inspection of the cylinder and piston showed no real sign of damage at all. you might not be so lucky though...

laramie

[snarf]

That sure sounds like the throttle slide bouncing around. If you twist and chop the throttle with the bike off, and let the slide bottom out, it makes EXACTLY that sound. Id check throttle cable slack and adjust it a bit tighter if its loose.

In your vid, if you give it some throttle [ie taking the slack out of the cable or suspending the worn slide] the sound goes away.

I'm no RFS expert, but obvious you should check simple things first before you tear into the engine...