5 replies to this topic

Posted February 28, 2002 - 02:08 PM


i'm getting a little popping under deceleration,i've sealed the pipe joint , i'm a bit confused over this fuel screw thing, i'm not sure my 400 even has this "fuel screw"?? it's not bad but enough to bug me a bit. what do i need to do??if anything. thanks jimbo

  • rmarion

Posted February 28, 2002 - 03:14 PM



Yes you have a fuel-mixture screw, its on the underside. Check out the new

I know I gonna get ripped a new one here, but its works for me.
On my 99-400 w/ PC exhaust, a factory Yamaha test rider (Not Mr. Dr. D) told me the bikes a set to lean, he had me go richer, main, pilot, needle, which I did. I have instant throttle responce, no sputter, cough, or hic up off bottom.



Posted February 28, 2002 - 03:57 PM


OK I'M FUNFUSED,lol, i've went up on the jetting 180 main,cant remeber pilot, i have instant throttle response and i haul butt, no problems anywhere just the decel popping that's what i want to fix, and mind you its not bad at all i was just wondering if i can eleminate it completely or can i expect some?and i'm totally confused on the fuel screw thing is this the air-screw the manual refers to??nothing in the manual refers to a "fuel screw" unless i'm missing it. jimbo

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  • 98yz

Posted March 01, 2002 - 05:29 AM


Not totally familiar with the 400, but on my 01 426 the screw (air screw, pilot screw,etc) is on the front bottom of the carb. I use a flat head screwdriver bit, you know the ones designed to fit in a 1/4" dirve that you can change out. I adjusted my 426 becuase of the same problem, and did away with most of the pop, I have a 45 pilot jet on the way to erradicate the problem.
Maybe this break down will help

Item 23 is the adjustment screw you need to work with

Posted Image

[ March 01, 2002: Message edited by: 98yz ]

[ March 01, 2002: Message edited by: 98yz ]

  • JBM

Posted March 01, 2002 - 06:27 AM


I have found that I get the best response when there is slight popping on decel. This is a lean condition at closed throttle. This can be adjusted, as mentioned with the fuel screw at the bottom of the carb. If you have to go out to about 2 3/4 turns then you should probably go up on the pilot jet. Fuel screw out to richen, in to lean the mixture. The fuel screw and pilot jet affect the mixture at closed to about 1/4 throttle. Again slight popping on decel should not be much cause for concern.


Posted March 01, 2002 - 06:57 AM


o.k thanks guys, mines so slight i dont think i'll worry about it the last time out it was pretty cold so maybe thats why i noticed it a little more than before, i looked at my notes and my jetting is 180/45 so i'm right on there i believe. thanks again jimbo :)

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