2005 YZF 450 Problem - need help!!!

My YZF hesitates to get down to idle when I close the throttle. It stays at 2000 for a second or two before it settles down to 1500. Pilot jet is 48, everything else is stock - what can I do to cure this?



I believe that's a sign that your pilot jet is off. My wife's CRF250 did that and I put a leaner pilot jet in it and it squared it away. First things first though is to make sure your throttle, throttle cables and the carb all move freely and aren't hanging up. After that I would tinker with the fuel screw to see if it helps when you screw it in (leans out the fuel mixture). Somebody here can give you some tips on jetting for the 05. What altitude are you at? I don't idle my bike that high but that's a personal setup.

sounds like a problem some have after installing new grips, and like pk says check the throttle cable real good. did you have a recent get off? the upper plastic part on one of the throttle cables broke on my 06 after a get off and the only reason i noticed it was the throttle kept sticking just a little bit when letting off so i finally pulled the little cover back and saw it was broke, looked fine from the out side. cables were cheap too, only like 30 bucks for the set.

Thanks for your suggestions but the bike is 5 hrs old - never fell off. All slide/cable move freely. The reason of my problem is the idle speed - if I set the idle to 1000 revs it works without hesitation but I want the idle nearer 1500 minimum. As it was bad with the 45 pilot jet and playing around with the fuelscrew didn´t help I put in a 48 with a slight improvement. Now I have fitted a 50 and have to close the fuelscrew completely to get an idle of around 12/1300. As soon as I raise the idlespeed to around 1500 the hesitation starts again and lasts for several seconds. Should I go even larger? Seems funny as best results are with screw fully closed....

Thanks for any ideas


The reason it runs better w/the fuel screw closed is due to the pilot being tooo big!! Unless you have piped this bike a #45 pilot will work well. I also have a 05 450. I did put a #48 in mine, but only after a pipe mod. Go back to a #45 and start w/the fuel screw approx. 2 1/4 turns out as a base. This is if you live between sea level and approx 1500 feet elevation. Good luck.

How far out is your fuel screw turned? Hanging idle is genarally caused by an air leak, or a too lean mixture. Be sure your hor start closes completely, that none of your intake valve clearances are too tight, and that there is no other source of an air leak between the carb and engine. Then set the idle mixture. You should end up with the screw roughly 1 3/4 to 2 1/4 turns out.

Thanks for the hints - here is what I have done so far. Checked the valves, two inlets were too tight, one exhaust too lose. Rectified everything and hoped for the best. Checked the hotstart as well - it seats properly with about 3mm play in the cable. I will try the 45 pilot jet and even a 42 tomorrow and report back. The exhaust is the stock euro version (I live in Germany) The altitude I ride most time is around 1000mtrs above sealevel (around 3000 feet)

The bike starts easily hot or cold, it reacts to the hotstart as it should, I can whack the throttle and it doesn´t bog down, it pulls good - everything is fine except that idling problem...

Thanks for your help


Tried the bike in my garden - the valvejob did not cure the problem...

Generally if you have a valve issue, it will make the bike hard to start. If it's 5 hours old, you shouldn't have valves out of adjustment. how far out were they? Blue4ever has the same bike and has been through a similar experience, I would go back to a 45 if you have the stock exhaust on it. What altitude are you at? Gray also brings up some valid points, check all the air boot connections, make sure the carb is seated in the boot and the clamps are snug.

Hello PK

I checked the valves: inlet left and middle were less than 0,10mm, around 0,07 so I corrected to 0,12, right inlet was okay. Exhaust left was over 0,30, corrected to 0,20, right exhaust was okay.

Riding is done at about 1000mtrs altitude (3000 feet), temperature between 15 and 25 degr Celsius. All connections,clamps etc are tight. Airfilter is clean and lightly oiled. I was racing mainly sidecar MX in the last twenty years and qualified for european licence so I know how to check valves or clean a filter etc. What I want to achieve on the YZ carb is to have a bit more fuel when the engine is decelerating and less fuel when it arrives at the set idlespeed. As soon as I get it to decelerate properly it will not hold the set idlespeed and rev to low. As I never had a carb like this before in my hands I don´t know enough of these things to make it work the way I desire. Had plenty of bikes before (3 Husabergs, KTM, Vertemati, Honda CRF) with all sorts of carbs on them and was always able to set them up the way I like it - but not this f***ing Keihin!

I guess I have to take the brand new carb completely apart and check every possible measurement etc - something is not working as it should. On my 04 CRF I was able to set the idlespeed anywhere between 800 and 1800 revs without the need to touch the fuelscrew - almost forgot that there is one! The Honda always decelerated promptly to my set speed without hesitation....

Anyway - thanks for all your suggestions - if I find the fault I report back.

Will try to find another Yam 450 rider with a 05 model to swap carbs and see if I get a difference.


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