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YZF_MXracer71

08 yzf 450 carb questions

5 posts in this topic

I have a 08 yzf 450 that starts hard only when it sits for a day or 2. if i twist the throttle once or twice is likes to

fire up much faster. one other issue is from a steady 3/8 throttle and down to an idle it will purr then have a

quick skip or hiccup. at half to full it has no skip. my valves are adjusted correctly and the carb is clean. im

assuming that it needs to be richened on the bottom end? what do i change to give it more fuel to help start and

give more fuel on the bottom. thanks for any advice

i also have an 06 250f and it fires up in 1-3 kicks no matter how long it sits.

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The part about priming a cold engine with the throttle is normal. If you richen the idle circuit to cover that, you'll end up with a bike that's a PITA to start when it's hot, and may be more prone to flaming out when you chop the throttle quickly.

Not entirely understanding your complaint about 0-3/8 throttle performance. Be sure your pilot circuit is correctly trimmed:

http://www.thumperfaq.com/jetting.htm#PJ

If you end up with less than 1 1/2 turns out, the pilot is too big. More than 2 1/4 - 2 1/2 or so and it's too small.

You might find that you like the NFPP needle better also. (PN 5TA-14916-PP)

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From zero to 3/8 and anywhere inbetween if i hold the throttle steady on a straight away about every 3-4 seconds it will almost act like it skips. and thanks for the info gray.

P.S what does NFPP mean. thanks again

Edited by YZF_MXracer71

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The 4 letters are a coded designation of the needle dimensions. If you learn what the codes indicate about the shape and how the shape affects the way it works, you can compare one to another and decide how you want to change what you have more accurately. All the info is in section 7 of the manual.

Got one?

http://www.yamahaownershandbook.com.au/?r=0

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