04 yz450f wont idle.NEED HELP!!!

[mxrider37303]

ok iv been trying to get this thing to idle for weeks now and im haveing no luck i checked the vavles and jetted the carb and and moved the needle clip to 4 and checked the leak down and cant figure out y it wont idle.it runs for just a few seconds and then dies.it sounds like its still lean but when u adjust the fuel screw it doesnt seem to effect ne thing.it seems to be ok 1/4 throttle and up.ne opinions and ideas thanks oo yea and it has a new hot start cable on it and a drd pipe..




THANKS

 

[IndyMX]

err.. did you try adjusting the idle screw?

 

[helio lucas]

or cleaning the carb?

 

[Ol'89r]

or cleaning the carb?

Make sure your pilot jet is clean. Remove it and make sure you can see daylight through the hole. Also, clean the pilot air circuit and all related orifices.

 

[mxrider37303]

the carb and pilot jet has been cleaned and if i adjust the idle screw high then the bike will idle ok but it sounds like its around 3500 rpms or so

 

[mxrider37303]

stock idle is between 1900-2100 rpms rite

 

[mxrider37303]

dam this yamaha lol

 

[Ol'89r]

If you are sure your carb is clean, then do a compression test.

De-activate the auto compression release and check your compression. A leaky valve will cause an erratic idle.

 

[Porkchop]

hey 37303, You have just been given good advice from one the best guys around, free of charge, courtesy of this great site! good luck & happy 4th! P.C. :ohmy:

 

[mxrider37303]

If you are sure your carb is clean, then do a compression test.

De-activate the auto compression release and check your compression. A leaky valve will cause an erratic idle.

how do you de-activate the vavle?

 

[Ol'89r]

how do you de-activate the vavle?

On the '04 you will have either a lever activated decompression release or a centrifugal unit on the exhaust cam itself. If you have a decompression lever on your handlebar then, just don't pull it when you check your compression.

If you have a centrifugal decompression unit on the cam, remove the top cover on the head to expose the cam and lift the little counterweight next to the camwheel to the open position and lock it in place using a piece of wire or metal clip. Then, check your compression.

If you are unsure about how the centrifugal unit works, refer to your manual.

 

[mxrider37303]

k thanks

 

[Matt90GT]

03 is the first year on the dirt bikes of the autodecomp cams in the yamaha

So you said you did a leak down test. What were the results????

 

[mxrider37303]

k new prob the pilot jet fixed the idleing now somewhere around half throttle the bike sputters and when u open it up runs like a champ not if u move the needle clip up on the 2 notch(witch it was on the 4 notch down)it runs way better parshall throttle and full but it wont idle...

the bike has a drd slip on and a mooseracing jet kit with a .45 pilot jet and a 155 main jet

 

[BSWIFT]

I agree with '89r. The jetting numbers look good but the bike still runs bad, suggests the jetting is still not right. 2 identical bikes could require different jetting so the numbers just give you a baseline indication.
Biggest mistake in jetting for novices like me is making more than 1 change to a the carb at one time. It's tough to be patient and get 1 circuit right before moving to the next. It is extremely important to start with the pilot circuit AND get it right before moving to the other circuits. A valve that is not seating properly will give you inconsistant results in jetting and make it appear properly set 1 second and then off just a few seconds later. At higher RPM's, a slight leak in a valve reduces power but on a 450F an average Joe won't notice it. From what you've posted, you seem to be chasing a jetting issue that is really a valve issue.
If indeed you have a valve not seating properly, resolving that will allow proper jetting to be acheived fairly quickly. Adjusting the needle clip and the accelerator pump timing will then allow you to maximize your throttle response.

 

[mxrider37303]

well finally fixed it.it dont make much sense to me but o well i guess. i put a 52 pilot jet and a 140 (dyno jet) main jet and used the stock needle clip on 2.i just dont understand y such a lean main jet,but thanks for all the help