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okay okay another jetting question

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Out on the track today for the first few laps I had been making pretty good times. Really muddy out and pretty crappy over all. Like I said though, first few lap times were okay, then when I started to open it up whenever I'd come up to the big doubles my bike would almost "studder". Just about midrange through the throttle. In 3rd that is. When I'd run up to them in 2nd wot, I'd clear the shit out of them and half the time over shoot them, but anything midrange and it wasn't smooth at all. Itd studder and skip and I'd loose momentum. I have a 140 main jet in it right now and the carb is clean as a whistle. The valves are good and overall, the bike is in great condition. Just curious as to maybe what I should do. Obviously a jet issue but my shop is closed for a couple days for the holiday. So, suggestions as to a jet size to go to would be nice. Thanks in advance!

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140 is not the number of a jet that is suitable for the KXF. I guess you meant 170 or 180. It should run pretty well with either of those.

Also, I think you are confusing the "midrange" and "midrange throttle" thing.

The jetting does not correspond to different revs of the engine. It does not matter at what RPM you have a problem. It´s at what degree of throttle opening.

If it runs good at wide open throttle the main jet size is OK.

If it is at half steady throttle I would try moving the needle one clip position.

If you suspect it to "blubber" from being too rich, move the clip one step upwards. This will lower the needle and make it a bit leaner at half throttle. If the problem gets worse, move it in the other direction.

In general, when it´s muddy and raining, you should jet it a bit richer for 3 reasons; 1.colder air has more oxygen in it. 2.the bike will be heavier from mud and is under a greater load. 3.oftentimes you go slower and rev a lot + the radiators can be clogged from mud which increases the engine temp. There is some safety for the engine to be had to be on the rich side in these conditions.

If on the other hand, it blubbers just at the moment when you wick it on, it could be the accelerator pump circuit that is clogged, or the maybe the timing screw has backed out.

Here is a chart that shows at what opening the different jets come into play:

mikuni_throttle_opening.gif

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Midrange by half throttle. Anytime its half throttle it does it. What exactly do you mean by lower/raise it by a clip? Screw in screw out the jet?

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Midrange by half throttle. Anytime its half throttle it does it. What exactly do you mean by lower/raise it by a clip? Screw in screw out the jet?

At half throttle the needle clip position is mostly responsible. This is quite obvious if you study the picture for a minute.

The needle hangs under the throttle itself.

It is adjusted by moving a c-clip into different grooves, or by changing to a differently tapered needle.

Move the clip one position down from where it is now. Ride the bike and see if it gets better.

2zgc6sy.jpg

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I'm on my lunch break, just moved it down and I'm going to ride it when I get home. It all makes sense. Definetly appreciate the help. I somewhat understand jetting but not to the extent that I should. Ill let you know the results this afternoon.

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Dk not to interrupt but hos definitipn has changed. He claimed in his first post that he can clear the bike wot on 2nd in upper rpm but im asuming he gets a bog studder in mid range rpms with wot in 3rd. Or are you unable to keep the bike in mid range in any gear? Reason im asking is if wot is fine in 2nd can get you to the rev limiter can you achieve it peak rpms in third? If you cant can it be done in 4th. If you to run the bike in 2nd will it studder also if trying to maintain mid rpms. Allthough mid rpm in 2nd is hard just because its so torqy. Reason im asking is to figure out if which side of the jetting its in.

I mean in third from low rpm with wot will it wind out fine. Or does it stutter in the middle no matter what?

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Dk not to interrupt but hos definitipn has changed. He claimed in his first post that he can clear the bike wot on 2nd in upper rpm but im asuming he gets a bog studder in mid range rpms with wot in 3rd. Or are you unable to keep the bike in mid range in any gear? Reason im asking is if wot is fine in 2nd can get you to the rev limiter can you achieve it peak rpms in third? If you cant can it be done in 4th. If you to run the bike in 2nd will it studder also if trying to maintain mid rpms. Allthough mid rpm in 2nd is hard just because its so torqy. Reason im asking is to figure out if which side of the jetting its in.

I mean in third from low rpm with wot will it wind out fine. Or does it stutter in the middle no matter what?

Midrange through every gear it stutters. I adjusted the clip down one so when i get home I'm going to put the bike back together and hopefully I'll be good to go. Let me know what you think. Really though, every gear, as soon as I get from 1/4 to 1/2 the throttle it starts to stutter. When I open it anything past 1/2 it rolls on beautifully. And just before 1/4 it's smooth as well. Note, I'm talking throttle here. RPMs are what's stuttering. It's the throttle that's from 1/4 to 1/2 when it happens. Hopefully that clears things up a bit. JUST to make sure too, my c-clip WAS at the second to top clip. IE, starting from the top, skip the first one it was on the second one. Bad place?

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Well it depends on. The needle but that would

Be a lean condition. It could be the issue. Stock needle should be middle or 4th clip down. Ncys needle is can be from 2nd to 4th depending on altitude.

Did this just start or allways been like this?

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Well it depends on. The needle but that would

Be a lean condition. It could be the issue. Stock needle should be middle or 4th clip down. Ncys needle is can be from 2nd to 4th depending on altitude.

Did this just start or allways been like this?

Always been like this, I just started opening it up cause I just bought it last week. I don't know what type of needle it is though. So basically my bikes running lean through the midrange? it's at the 3rd down now so I'll try that and see where it is. I want an iPhone, i hate my blackberry.

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Ive got a dingleberry for work i like the keyboard but its slow. The iphone is great but the touch screne keyboard sucks and no scroll ball is a pain.

Is this an 08 or 09 and is it used or brand new? If new i would asume its just the needle. If you are in southwest mi by indiana you can bring it out and i can help you. Good luck

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Ive got a dingleberry for work i like the keyboard but its slow. The iphone is great but the touch screne keyboard sucks and no scroll ball is a pain.

Is this an 08 or 09 and is it used or brand new? If new i would asume its just the needle. If you are in southwest mi by indiana you can bring it out and i can help you. Good luck

I'm up in the PNW haha. But its actually an 04.

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