| Jetting Suggestions Wanted [message #777850] |
Thu, 13 July 2006 20:12 |
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I have a '97 YZ250 with the following extras:
FMF PowerCore II Silencer
FMF Gold Series Fatty Pipe
Boyesen Dual Stage Reeds
Main Jet 175
Pilot Jet 50
Needle clip is in middle position (3)
50:1
3rd, 4th, and 5th gear are excellent and pulls hard in all throttle
positions. 1st and 2nd gear however are not so good. Power only seems
to kick in at the very top of 2nd gear right before you have to shift.
1st gear, there seems to be nothing at all. In both gears, it seems to
sputter a little. Any suggestions on how I should proceed in regards to
trying to remedy the lack of low end power like jet sizes and such?
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| Re: Jetting Suggestions Wanted [message #777894 ] |
Fri, 14 July 2006 06:43 |
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In article <1152814346.926565.14060 [at] 35g2000cwc.googlegroups.com>,
jpgreenleaf [at] gmail.com wrote:
> I have a '97 YZ250 with the following extras:
>
> FMF PowerCore II Silencer
> FMF Gold Series Fatty Pipe
> Boyesen Dual Stage Reeds
>
> Main Jet 175
> Pilot Jet 50
> Needle clip is in middle position (3)
> 50:1
>
> 3rd, 4th, and 5th gear are excellent and pulls hard in all throttle
> positions. 1st and 2nd gear however are not so good. Power only seems
> to kick in at the very top of 2nd gear right before you have to shift.
> 1st gear, there seems to be nothing at all. In both gears, it seems to
> sputter a little. Any suggestions on how I should proceed in regards to
> trying to remedy the lack of low end power like jet sizes and such?
My '99 has same pipe, reeds and silencer. There are a few differences in the
engine (different bore & stroke) but it looks like it uses a very similar carb.
I've settled on the following baseline jetting for 500' elev. 65 deg. riding in
No. Cal.:
Main Jet 168
Pilot Jet 42
N4DF needle at #2 position
Air screw out 2.5 turns
36:1 Yamalube 2R
I don't know what is the standard settings for your bike, but I'm running leaner
than yours. Ignore the main jet for now, I rarely ride with the throttle where
the main jet makes much difference. Start by leaning the pilot jet one or two
steps at the most and see if it improves. If it does, try a step or two leaner
still, and see if it improves again. If it doesn't, go the other way and see if
that makes a difference.
Once you've got the pilot circuit tuned, do the same with the needle clip/air
screw settings.
Lastly, work on the main.
Make sure you've got a clean open silencer.
Write down each change; if I don't I tend to forget what I did the week (or
month) before. Good luck!
--
Charles
'99 YZ250
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| Re: Jetting Suggestions Wanted [message #777932 ] |
Fri, 14 July 2006 17:50 |
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HardWorkingDog wrote:
> Start by leaning the pilot jet one or two
> steps at the most and see if it improves.
Good advice overall, but I don't recommend starting with the pilot.
The pilot only covers just off idle and costs brass. Changing the
needle clip position is the easiest tweak, covers meat of the throttle
positions, and doesn't cost anything.
I suggest moving the needle clip two positions up (making the needle
sit lower - this leans out the mix primarily in the 1/4-3/4 throttle
range) - you'll know right away if your headed in the right direction.
If everything improves, then attack the brass and start the full
jetting procedure.
Do a search on "Jetting FAQ" - you find some good documents on jetting
theory and procedures.
JMHO - Jay
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