Just bought my first 4-stroke and it keeps dying.

I just got a new 2004 yz450f and cant keep it running. It seems to die when i go down a hill and lock up my rear wheel, as well as when i pulled in the clutch to ride the berm at the bottom of the hill, and it died on flat ground when i hit the rear brake hard and yes i did have the clutch pulled in all the way, or it also died when doing a small step up in mid air i just fell over cause it was a steep hill, it will run fine if i come to a slow stop and have the clutch pulled in but after a quick break where the rear wheel locks up or as soon as it locks up it wants to die. Is this just the idle speed that needs to be adjusted????

Also i read the manual but any break in and maintance tips. Today i just putted around mainly in second gear for about an hour, and do the piston rings really need to be replaced every five times out!

Thanks for any help you can give me.

Almost sounds like your clutch may not be fully disengaging when you pull in the lever. Adjust it per the spec in the manual and see if that helps out. With no extra flywheel weight they are more sensitive to stalling but you should not be having that much problem, provided the clutch is working as it should.

Did you adjust your fuel screw?

Maybe it's just barely staying running due to lack of fuel in the pilot circuit and the drag from the clutch is enough to kill it.

Mine wouldn't idle until I put my screw 2.5 turns out...

As for changing the piston rings every 5 times out, who the hell told you that?

Maybe every 500 times out...

I will bet your float level is too high! It makes sense, especially after you say it happens going downhill into a corner or under hard braking. Check the float height. :devil: Before I removed the carb to set the float height, I would turn the idle up a bit and see if it helps. If it keeps dying under deceleration or going downhill it will be the float. Higher idles do make you go faster! We all turned them up in roadracing, you couldnt even coast slowly thru a turn. :awww::thumbsup:

I would do some various riding and pay real close attention if you are disingaging the clutch fully when the rear brake is locking. with the high compression of the bike it dont take much to stall... an 8-10 oz flywheel weight would help lots if that is the case.

I would not go that high for a flywheel weight unless you are woods riding. There has been many good suggestions in this thread. The only thing I would add is more of a question. Why are you locking up your rear wheel so much? While you should be able to without killing the bike, it is a common mistake novice riders do when entering corners. Unless you are qoing to square a corner off, or have to pull the clutch in near the apex of a tight turn, there is no need to pull the clutch in every time you use the brake hard. When braking down a hill (which is most likely going to have braking bumps on it if there is a corner at the bottom) you should not be pulling the clutch in just because you are on the brakes hard.


Just turn up the idle!!!!!


Bonzai :thumbsup:

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