snap the throttle open and engine dies

Well today(tuesday Aug.2) I took my newly bought 03' yz450 out to ride. Hell yeah! This bike is off the chain! First I want to confirm my ignorance to a few of you about my knowledge and the questions I asked in the past week. This bike definitely needs more traction in the rear! Forget about weight savings idea, I want a 120/90-19 Maxx Cross IT rear tire. Will it fit on the stock rim? I hope. Also when I snap the throttle open really quick the engine dies. My 250f was kinda the same way but is there something wrong with it? I noticed the engine itself excluding the exhaust is louder than 250f. I think I hear crank noise. I could hear top end noise on my 250f but even more on the 450. I know that the yzf's have more moving parts than crf's so you will hear more engine parts moving around, but what is considered excessive(engine noise)? Please reply to this list of questions, I know I ask alot but these are more important than the others. :D 2003 YAMAHA YZ450F :D

same problem on my yz426 since the piolet jet combo (3in all) are used in 1/8-?? movement I'm gonna try and lean er out some.....

You can work on it, and you can improve on it, but you'll probably always be able to gag a big 4-stroke single by snapping the throttle from idle to wide open. This is especially true in neutral, where the timing is different. Learn to "roll" the throttle. In this maneuver, you open it more slowly at first, and progressively faster as the engine responds. Once you get it, it will become second nature, and the engine will respond almost instantly. Too anyone watching, it will look like you snapped it open, even though you didn't. Just a part of the 4-stroke skill set.

The 120 will fit. I use one. They're big, and a little heavy, but they bite, and they wear really well.

Compare the noises yours make to another one. That's the easiest guage of what's normal and what's not. One noise you'll certainly hear is gear box rattle. It's a sort of growling at an idle in neutral. Pull in the clutch and/or put it in gear and it will go away. It's normal. It's louder than your 250 because everthing inside is bigger and heavier.

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