YZ400 Jetting?
DSinz
seems to run pretty well. Is the stock jetting set up for a wide range of
altitudes? My elevation is approx. 100ft . I have only ridden one other 98 and
it had stock jetting as well.(same altitude) I am new to four strokes and don't
know what the signs and symptoms of improper jetting are. Any input or
opinions would be greatly appreciated.
Dave
99 YZ400
Rowdy
As you are mentioning it, i am facing the following feature / bug at
my WR400F:
1. perfect idle, responds fine to idle mixture adjustment screw, bike
starts easily and doesn't stall often.
2. throttle opened VERY slightly: gives me a bit higher idle, but no
as smooth sound as before.
3. throttle opened for a very little bit more: even higher idle (2000
rpms?) that eventually bursts off to app. 4000 rpms ???
4. from there on the relationship between throttle position and rpms
is linear again, throttle response is crisp.
5. closing the throttle just below the amount of point (3) makes the
rpms drop back down to high, rough idle again.
this happens with the engine warmed up well, gearbox in neutral, air
filter cleaned, and the stock #45 pilot jet as well as the #40 that i
installed (because i assumed the effect at (2.) being caused by a rich
pilot jet).
this effect is not noticeably in racing condition in a special stage
<VBG>, but sometimes when trying to very slowly drive away from a full
stop.
I'd say, that behavior is similar to a two stoke engine's transition
into the 'meaty' part of it's power band (as seen & felt on a KTM360
:)
is that normal for the YAMAHA 400 strokers ?
is my jetting off ?
can the throttle position sensor be the cause ?
am i chasing a ghost ?
do i abuse my WR's power band :-) ?
do i have to live with that effect ?
mind you, the bike doesn't stall or bog due to that effect, it only
makes me pace off more than i intend. (it's o.k. for showing off at
the ice cream café, though :-D)
any experiences ?
Rowdy
WrrRRRRRRR400F
Nitrous Oxide
thus:
>I am pretty much ignorant as far as jetting is concerned. I have a 99 and it
>seems to run pretty well. Is the stock jetting set up for a wide range of
>altitudes?
A feel test by riding from sea level to 3,000 ft and checking temp
will probably give you a sense of what is going on.
> My elevation is approx. 100ft . I have only ridden one other 98 and
>it had stock jetting as well.(same altitude) I am new to four strokes and don't
>know what the signs and symptoms of improper jetting are.
Try a full bore plug chop. ie flat out for a 1/2 mile or so (not
necessarily in top) and hit the kill switch and dip the clutch. This
will show you the plug colour for the main jet which should be a
tan/light grey colour. Make sure your plug is not brand new and
already has some miles/colour on it first.
Symptoms of too rich will be a black insulator and too lean a white
although plug heat range comes into play too.
Try www.dynojet.com too. A dyno test also gives some insight as does
the CO meter they use.
> Any input or
>opinions would be greatly appreciated.
Dave I'd post my info here but it's all in tables and will wrap if
posted here so please extract the relevant parts from my XR4FAQ, on
jetting.
http://www.motorcycle.co.uk/XR4FAQ/
There's indications of what parts do what in the carb and the order of
adjustment plus a spreadsheet for altitude and temp along with
variations in jetting for mud, rain etc. Ericc Gorr has some good
stuff on carbs/jetting also but can't remeber URL.
http://www.motorcycle.co.uk
Brevis esse laboro, obscurus fio
Remove^nospam^. to reply
HBGJockey
wrote:
>As you are mentioning it, i am facing the following feature / bug at
>my WR400F:
>1. perfect idle, responds fine to idle mixture adjustment screw, bike
>starts easily and doesn't stall often.
>2. throttle opened VERY slightly: gives me a bit higher idle, but no
>as smooth sound as before.
Take the carb off, move the throttle the same way you did and look at
the amount of fuel the pump injects - this should explain everything!
After you have been enligthed, write down 1.000 times: I shall not
operate my WR's throttle like a whimp!
BTW, I'll be at the Reitwagen Cafe Thursday at 19:30.
Michael
************************
* mpe...@ibm.net
*
* 98 Yamaha WR400
************************
Cam Mitchell
(Nitrous Oxide) wrote:
>Try a full bore plug chop. ie flat out for a 1/2 mile or so (not
>necessarily in top) and hit the kill switch and dip the clutch. This
>will show you the plug colour for the main jet which should be a
>tan/light grey colour. Make sure your plug is not brand new and
>already has some miles/colour on it first.
Doesn't that only work for the main jet?
--
ICQ #15223254
94 KX500
Barry D. Klein
Cam Mitchell wrote:
I've just been through this on my DR350 after changing airbox and
pipe. I had trouble with plug readings and better luck with seat of the
pants feel. Mine was too rich in the main jet, giving a "missing" or
"coughing" sensation at full throttle. It almost seemed like an ignition
problem. This was solved by going leaner until it revved all the was up
smoothly.
Mine was also too lean in the needle position. The symptoms were an
"out of gas" hesitation when rolling throttle quickly from 1/2 to full.
Raising the needle fixed this.
As far as the pilot and fuel screw go: adjust the screw for max idle
rpm. Turn the screw in (leaner, assuming the YZ has a fuel screw rather
than an air screw) until rpm drops. Then turn out to enrichen for max
rpm. Adjust idle speed screw if rpm is too high and repeat. If you are
much more than 1 turn out, go to a richer pilot. The bike should then rev
smoothly from idle to 1/2 throttle without cough or hesitation.
Hope this helps.
Barry
Leon Rawls
Pro-meg pipe and The exhaust cam retarded to YZ specs. So I was thinking I should
set the carb to YZ specs too. So I removed the Thing off the right side of the carb
that hooks up to the intake port and plugged off the carb. And changed the main
jet, needle, and main air jet to YZ specs. The bike ran good but Popped bad when
you let off the throttle it was noticeable big time on the street. I tried to fix
it with moving the needle and fuel screw but it still popped . Then I put back the
vacuum thing back on the carb and then put it back to WR specs with one size bigger
main 172 and the bike Idles better runs better (it rips!) and NO MORE POPPING! That
vacuum thing on the carb works! what ever it is.
Nitrous Oxide
Mitchell) did cut boon whids thus:
>On Tue, 15 Dec 1998 09:56:39 GMT, nitrous@^nospam^.motorcycle.co.uk
>(Nitrous Oxide) wrote:
>
>>Try a full bore plug chop. ie flat out for a 1/2 mile or so (not
>>necessarily in top) and hit the kill switch and dip the clutch. This
>>will show you the plug colour for the main jet which should be a
>>tan/light grey colour. Make sure your plug is not brand new and
>>already has some miles/colour on it first.
>
>Doesn't that only work for the main jet?
Who's not reading his posts Cam ;) 3rd line.
Flash
compare how your bike runs now and when it was stock? I'm considering some
of the same mods. Is the pipe worth it?
Flash, 98WR400F
Leon Rawls <suz...@inetw.net> wrote in article
<36777329...@inetw.net>...
Rowdy
>
> Here a little info I have an 98WR400 ( that's street legal) with a White Bros
> Pro-meg pipe and The exhaust cam retarded to YZ specs. So I was thinking I should
> set the carb to YZ specs too. So I removed the Thing off the right side of the carb
> that hooks up to the intake port and plugged off the carb. And changed the main
> jet, needle, and main air jet to YZ specs. The bike ran good but Popped bad when
> you let off the throttle it was noticeable big time on the street. I tried to fix
> it with moving the needle and fuel screw but it still popped . Then I put back the
> vacuum thing back on the carb and then put it back to WR specs with one size bigger
> main 172 and the bike Idles better runs better (it rips!) and NO MORE POPPING! That
> vacuum thing on the carb works! what ever it is.
Hi Leon!
That vacuum thingy you're talking about is called 'Coasting Enricher'
in
the KLX650R spare parts list!
It looks exactly the same on our WRs.
Having slight troubles winter jetting my KLX650R last year, i blocked
the mechanism to see if it is the source of my troubles.
Instantly the KLX started popping extremely loud, a real cop's head
twister!
What it does:
With the throttle fully closed and the engine at decent rpms (>1600)
the vacuum (sic!) actuating against a small, air tight
membrane, overcomes the spring in the device and closes the
second air canal (KLX) to the pilot jet, resulting in a much richer
mixture
thus preventing the popping.
I never understood why people trying to 'YZ' their WR (exhaust cam,
cylinder base gasket, et.al.) are reporting they were removing the
coasting enricher, too.
I'd say you were right reinstalling the coasting enricher, it doesn't
eat any power and represents only a minimal weight penalty <G>.
At least here in good ol' europe, loud bikes won't help our image.
Rowdy
P.S: what did you do to the air box and air box lid duct ? still
stock ?
Leon Rawls
is a handful on tight trails now. The bike wants to wheelie all the time but I
like it. The great thing is if you don't like it you can always go back. The
pipe is well worth it though made a big difference maybe it would not have made
such a difference on the YZ but the WR has that big heavy EPA muffler on it. I
thing most people would do fine without using the larger headpipe the stock one
would work better. You lose a little bottom end with the WB larger headpipe.
Flash wrote:
> That's what it's there for. It's an anti-backfire device. How would you
> compare how your bike runs now and when it was stock? I'm considering some
> of the same mods. Is the pipe worth it?
>
> Flash, 98WR400F
>
> Leon Rawls <suz...@inetw.net> wrote in article
> <36777329...@inetw.net>...
Cam Mitchell
(Nitrous Oxide) wrote:
>>>Try a full bore plug chop. ie flat out for a 1/2 mile or so (not
>>>necessarily in top) and hit the kill switch and dip the clutch. This
>>>will show you the plug colour for the main jet which should be a
>>>tan/light grey colour. Make sure your plug is not brand new and
>>>already has some miles/colour on it first.
>>Doesn't that only work for the main jet?
>Who's not reading his posts Cam ;) 3rd line.
You're right John, sorry :) Is there a reliable way to check the
pilot jet with your spark plug?
(I can go up and down a few sizes on the 500 and not notice a
difference in power.)
I have it jetted richer than what everyone tells me to (a lot richer),
but I've never fouled a plug. My silencer packing gets soaked fairly
fast but the plug doesn't foul..