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Discussion Starter · #1 ·
when the machine is at idle and i whack the throttle it wants to stall. rejetting does not help. any suggestions? thanks.
 

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Does it do when you have a load on. Like when you are riding?? Remember it has an accelerator pump so if you whack the throttle at idle with no load it will dump a lot of fuel into the intake and cause it to do that, you can't jet a bike by reving it up' you need to ride it. But you could trying idling it up to 1500 rpm, and change the pilot to a bigger one like a 45 and see if that helps.
 

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Discussion Starter · #3 ·
I have a168 main 45 pilot needle on 4th clip, it does not matter if the lid is on or not. as far as being under a load or not it does not matter. thanks
 

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sounds like you need to take the lid off and lean her out a tick all through the range, if that dosent cure what ale's it. try richening, if it gets worse then take it to a shop that can tune it, or take it back to your dealer and tell them to make it right :)
 

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it doesn't matter how you jet it. it will always stumble a little off from idle. it doesn't have a constant velocity carb, and it don't have enough intake manifold pressure like a 2 stroke to give it that instanteous throttle response.
it sounds like your jetting is pretty close to what i would recommend depepnding on what you have done. if you're running without an airbox lid and no baffle in the stock muffler put the 42 pilot back in and turn the fuel screw out about 2 turns. if you have an after market pipe then turn it out 2 1/2 turns out from bottom.
adjust your idle between 1500-1800 rpm. you will get a hesitation if you just mash the throttle off idle, but it won't hesitate when you're riding it.
 

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Originally posted by killerkx327@Sep 22 2003, 06:54 PM
it doesn't matter how you jet it. it will always stumble a little off from idle. it doesn't have a constant velocity carb, and it don't have enough intake manifold pressure like a 2 stroke to give it that instanteous throttle response.
it sounds like your jetting is pretty close to what i would recommend depepnding on what you have done. if you're running without an airbox lid and no baffle in the stock muffler put the 42 pilot back in and turn the fuel screw out about 2 turns. if you have an after market pipe then turn it out 2 1/2 turns out from bottom.
adjust your idle between 1500-1800 rpm. you will get a hesitation if you just mash the throttle off idle, but it won't hesitate when you're riding it.
sounds like you know your jetting. I have a ? for you. I'm at 900FT, lid on, full HMF, 170 main, 45 pilot, blue JD needle on 3rd clip, and 2 1/2 turns on air screw. When my quad is hot it doesn't want to start without giving it gas. Everything else seems to be fine. Does it sound like a jetting problem?
 

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Originally posted by cjpoole1+Sep 23 2003, 03:08 AM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (cjpoole1 @ Sep 23 2003, 03:08 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--killerkx327@Sep 22 2003, 06:54 PM
it doesn't matter how you jet it. it will always stumble a little off from idle. it doesn't have a constant velocity carb, and it don't have enough intake manifold pressure like a 2 stroke to give it that instanteous throttle response.
  it sounds like your jetting is pretty close to what i would recommend depepnding on what you have done. if you're running without an airbox lid and no baffle in the stock muffler put the 42 pilot back in and turn the fuel screw out about 2 turns. if you have an after market pipe then turn it out 2 1/2 turns out from bottom.
adjust your idle between 1500-1800 rpm. you will get a hesitation if you just mash the throttle off idle, but it won't hesitate when you're riding it.
sounds like you know your jetting. I have a ? for you. I'm at 900FT, lid on, full HMF, 170 main, 45 pilot, blue JD needle on 3rd clip, and 2 1/2 turns on air screw. When my quad is hot it doesn't want to start without giving it gas. Everything else seems to be fine. Does it sound like a jetting problem? [/b][/quote]
ditto
 

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I agree with the last two guys. The only thing I have found is going to BLUE #4 and less on the mixture screw. That makes it better but it doesnt fix it.
Isaac
 

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I'm running the JD kit as well with a 170 main and 45 pilot, blue needle w/clip on 4th spot and ~2 to 2 1/2 turns on screw (at sea level). I also have the power valve. It runs great. I hardly had to adjust the idle at all. Very strong mid range and no hesitation. If I slammed the throttle down any harder I'd be lying on my back in the sand all the time. I also run with no lid, K&N filter, full HMF pipe and YZ cam. My only issue is I hit the rev limiter so fast I can't shift fast enough, but I have a 15 tooth on order for this. I can't even imagine the need to go to a 13.
To start my bike all I need is just a very slight constant pressure on the throttle and she fires right up (hot or cold), under load I can't get it to die when slamming in the throttle, If I push it in too fast I'm on my back anyway. But without a load it will die when slamming the throttle fast. Like others have mentioned it's an inherent side effect of a carb with no vacuum.

Hope this helps someone.

-Jason
 

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I have removed the spark arrestor on my yfz and it pops on deceleration. Does this mean I need to re-jet?
 

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Originally posted by cjpoole1+Sep 22 2003, 07:08 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (cjpoole1 @ Sep 22 2003, 07:08 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--killerkx327@Sep 22 2003, 06:54 PM
it doesn't matter how you jet it. it will always stumble a little off from idle. it doesn't have a constant velocity carb, and it don't have enough intake manifold pressure like a 2 stroke to give it that instanteous throttle response.
  it sounds like your jetting is pretty close to what i would recommend depepnding on what you have done. if you're running without an airbox lid and no baffle in the stock muffler put the 42 pilot back in and turn the fuel screw out about 2 turns. if you have an after market pipe then turn it out 2 1/2 turns out from bottom.
adjust your idle between 1500-1800 rpm. you will get a hesitation if you just mash the throttle off idle, but it won't hesitate when you're riding it.
sounds like you know your jetting. I have a ? for you. I'm at 900FT, lid on, full HMF, 170 main, 45 pilot, blue JD needle on 3rd clip, and 2 1/2 turns on air screw. When my quad is hot it doesn't want to start without giving it gas. Everything else seems to be fine. Does it sound like a jetting problem? [/b][/quote]
my yfz and my yz bikes have always needed a little shot of fuel when they are hot to restart.
the only thing i've been able to come up[ with, is the fact that the motor is very hot internally, therefore the intake ytract is dry, since the heat evaporates the fuel so fast, that it will need a little shot to get'er going again.
and i highly recommend taking the airlid off , especially at 900ft. then rejet accordingly.
one more thing, i recommend a yamaha CNVQ needle over the JD needle setup. i've found the yfz runs much more consistent and is easier to jet it right with the yamaha needle.
it is the needle out of the 03 yz 450 bike.you will notice the difference in power delivery. the yamaha needle gives you a more consistent torque curve on the dyno and more midrange and topend power. it's very small difference , but it's worth the $40 dollars for the jet kit.
 
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