YZ450 clutch and engine problems?

hey guys, i just bought a damn near new yz450 the other day with approx. 30 hrs on it. I just got back from a little ride and it didnt seem to be running right. First of all, the engine sputters or misses at around 7000 rpm. When revved up in neutral, itll cut in and out at 3/4 throttle. I think its runnin a litle rich cuz it pumps out a little black smoke when revved up.

Second, when im goin down the road in 3rd or 4th gear, it feels like the clutch slips. It'll feel like the clutch lever is pulled in for a second. This will happen about 10 times per minute. Tends to happen more under acceleration. Anyone know how to fix these problems? thanks

I think the first thing you need to do is get the jetting / fuel screw right. Are you sure the bike is "slipping" in 3 or 4th gear or is it cutting out/ bogging??

ya, im pretty sure its slippin. Just outa nowhere when drivin down the road it jerks when goin constant speed. i just took it out for another test to see wat was wrong and its also grabby when taking off, and makes a weird growling


go to the jetting forum and learn all you need to know about tuning that carb.There is lots of good info there

the 03' had a gabby clutch. Do a search here in this forum and you will find the fix for that. Basically it involves using the 02' parts.

I dont believe can get a true reading on how your bike is running by reving it in neutral.Iam not sure exactly how it works,but that little neutral saftey is to stop you from reving the bike to the hilt while in neutral.It does something to the spark or timing to prevent this.Black smoke is to much fuel,could be jetting or maybe just a little dirt in the carb.As far as the clutch goes my 03 is grabby but does not slip or anything under acceleration.Just because your bike has low hours does not means your clutch is not toast.The clutch can be fried very quickly if you slip it or basically ride it like a 2 stroke.

i did the reversal clutch plates mod and it still slips when goin down the road, but no more growling. Is there some kind of adjustment for the clutch that might solve this? ive still gotta do some work to the carb and ill change the spark plug and hopefully that solves something.

Regarding the clutch, make sure that there is play in the lever, approximately .125" there are three possible areas to adjust the play on the cable.

Is it possible you are hitting the rev limiter? If not we had a 450 that was using Ultimate 4 fuel that ate up the float and clogged the jets with the float material I had to order new jets and a float and clean the crap out of the carb it was a mess and that bike barely ran.

I know this sounds silly but have you checked your chain tension or rear sproket for missing or severely rounded teeth.

sprockets and chain are good

Could be a tranny problem too.... :)

i did some more looking up and found something interesting. Quoted from a previous forum " My 426 would jerk a little too when held at the same throttle settings in any gear. The reason was that I was lean. Why would it jerk at low speeds and not high speed or do you mean low rpm and high rpm. If it was rpm then maybe pilot? If you mean speed, eee I'm not sure. " does this sound right?

A transmission problem will occur only in the affected gear or gears under a load. You'll get a very pronounced "jerking" sensation like the gear is kicking in and out. The "in any gear" quote would indicate a lean jetting condition. A slipping clutch will occur in all upper gears at a progressively worse rate as engine speed or load increases.

Your problem is jetting 100%. Some 2003's enetered Canada with a 165 main. They were all supposed to have 172 main. They bikes that came with the US jetting als had smaller pilots (40) instead of the proper 42. If it feels like it's missing but only when it's using the most fuel (on the main circuit) go bigger on the jets. My suggestion would be a 172-175 main...step it up from 165-168,172...move your pilot up as well...go to 42, then 45. Buy a Zip Ty fuel screw adjuster right away ($U 20)...get that set as good as you can and then conquer jets & clip position. Don't get bogged down listening to guys talk about trans problems. You have a jetting issue plain & simple.

Good Luck, :thumbsup:

i have the same problem with my 02 426. it feels like the clutch slips but it is in 4th and 5th. i still have no idea what it is. it was doing it before i changed the clutch and still does it after the new one is installed. i don't think it is the jets because it runs fine. and not the sprocket or the chain. it does it on acceleration, but only in those two gears. good luck

Here's the golden rule I follow when troubleshooting:

Start with the easiest fixes first.

a. new plug

b. clean the carb and jet it properly

c. Get the extended fuel screw

d. make sure the clutch is adjusted properly at the lever

e. make sure you have the correct kind of oil in the bike. NOT energy conserving!

If the problem persists then move on to the clutch components..... I bet it's a dirty carb problem :ride:

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