XR600 carb- advice needed.
Warren Murray
I'm seeking any advice on how to improve the notorious XR-600 Keihin
carburettor. My bike, despite being only 3 yrs old, has the known traits
like cough stopping (particularly pesky), rough idling, missing at times
etc. The bike has had the exhaust baffle removed, though I'm going to
replace it with a performance baffle, & I'm wondering if this could be a
factor because the first thing any XR owner seems to do is chuck the
baffle out.
Aside from getting a Mikuni carb ($$$) are there any other options for
improving the performance of the original carb? What about air filter
mods, opening up the airbox etc? What about using a bell or "trumpet" on
the intake from the airbox to the carby, similar to a road bike - would
this make it run more smoothly?
Any advice and anecdotes are welcome.
--
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Warren Murray - q885...@mail.connect.usq.edu.au
The University of Southern Queensland
The opinion expressed is that of the writer,
and not necessarily that of the University.
Volker Bartheld
Hi Warren !
Warren Murray <q885...@mail.connect.usq.edu.au> schrieb am Tue, 25 Mar 1997
18:50:41 -0800:
>I'm seeking any advice on how to improve the notorious XR-600 Keihin
>carburettor.
Well, indeed, there's something to be improved as I (painfully) had to
find out...
>My bike, despite being only 3 yrs old, has the known traits
>like cough stopping (particularly pesky), rough idling, missing at times
>etc.
First of all (if not done already), check what jets (idle/main) have
been mounted in your carb. This can be done by simply draining the
carb and removing the float bowl. You can then access both jets from
below with a flat-tipped (idle jet) screwdriver and a size 8 (just
guessing) wrench (main jet). Standard is 62 for idle and 152 for
main. Mine had 62/125 which was *FAR* too lean at mid range up to top
end, resulting in coughing and pinging. A size 152 main is a good
choice if you stay with the standard (Honda Kritzman) exhaust baffle and
stock foam filter. If you tend to squeeze more power (especially the
top end) out of your engine, I would recommend the BajaDesigns
baffle and a TwinAir filter. Other riders experienced good results with
Uni filters (haven't tried yet). Some XRs come with a snorchel (the shop
manual calls it 'duct cap' - it's for the U model only) which is, in some
cases, riveted to the air cleaner case. Drill out the rivets and remove the
snorchel. This will help increasing the bike's response and doesn't add that
much to the breathing noise level.
>The bike has had the exhaust baffle removed, though I'm going to
>replace it with a performance baffle, & I'm wondering if this could be a
>factor because the first thing any XR owner seems to do is chuck the
>baffle out.
The stock Honda baffle is very restrictive. Besides the chance of getting
killed by my neighbour I noticed that taking out the baffle will add notice-
ably to the top end. I've been told, that the BajaDesigns baffle performs
nearly as good as the Supertrapp exhaust with a considerable lower price
*AND* noise level. This saves my neighbours day and my life.
If you perform such modifications, you'll have to adjust your jetting to
the new situation. If you live at (or nearly at) sea level, size 162 up
to 168 main jets are worth a try.
>Aside from getting a Mikuni carb ($$$) are there any other options for
>improving the performance of the original carb? What about air filter
>mods, opening up the airbox etc? What about using a bell or "trumpet" on
>the intake from the airbox to the carby, similar to a road bike - would
>this make it run more smoothly?
I don't have any experience with those modifications. To get rid of my
bike's nasty behaviour such as
- stalling when idling
- when RPMs are up and the throttle is closed, the exhaust makes popping
sounds
- slight hesitation when accelerating from idle RPM
I increased the idle jet size from 162 to 168, then 170 and finally 172.
You can do this if you find that adjusting the idle mixture screw
doesn't help. To find the correct idle mixture, set the screw in the middle
between too lean and too rich to get maximum RPM with a given idle speed screw
setting.
>Any advice and anecdotes are welcome.
You may also check, if the motor breathes 'false air' caused by improper
installation of the carburator insulator bands, the air cleaner connecting
tube or little holes in any rubber parts. Take a look at the 'air cut-off
valve', this is a little rubber membrane, located under a metal plate
at the left side of your carb. Any damage or deposits of fuel can cause poor
idle. Check, if all necessary O-rings are present, especially washer and
O-ring of the pilot screw (idle mixture adjuster). Both of them, O-ring
and washer were missing in my carb (the previous owner may have lost them),
resulting in additional air passing the screw's threads and leaning out
the mixture.
Last, but not least,
check for the correct (consult shop manual) size and position (clip 3rd/middle
notch) of the jet needle and check/adjust the float level to 14.5 mm (0.57 in)
by carefully bending the float tang if necessary.
If you need to clean the carb you can apply cleaning gasoline or use an ultra-
sonic bath cleaner and cleaning alcohol. Blow open all passages and jets with
compressed air before reinstalling, use a new carburator top cover seal and
clean the fuel tank / fuel strainer / fuel valve.
The procedure mentioned above took about one day and made my bike run like
new. Go ahead and try yourself !
Happy biking,
take care !
Volker
P.S.: Other modifications include cutting out the wire mesh of the air cleaner
assembly or totally replacing it. You can also have a look at the motor sided
rubber connector. Sometimes a little increase in diameter is still possible.
The same is true for the exhaust pipe. If the welds are overdone, you can grind
them down a little bit without weakening the material too much. Also available
are some aftermarket pipes with larger diameter which fit to the standard
exhaust. Perhaps the XR600R experts of r.m.d. can tell us more on that topic ?
P.P.S.: Thanks again to Jeremy Hansen. He did a great job teaching me the XRs
little secrets...
P.P.P.S.: Last one: Adjust your valve clearance and decompression system. It
can affect the idling qualities, too. I prefer adjusting the intake valve
clearance to 0.1 mm (0.004 in) and the exhaust valve clearance a little bit
on the loose side to 0.15 mm (0.006 in) to keep them cooler and gain a little
bit more low end torque.
Volker Bartheld <bart...@afmp04.mppmu.mpg.de>
XR600R '94: "One man, one cylinder."
Impulse
Warren Murray wrote:
>
> I'm seeking any advice on how to improve the notorious XR-600 Keihin
> like cough stopping (particularly pesky), rough idling, missing at times
> replace it with a performance baffle, & I'm wondering if this could be a
> factor because the first thing any XR owner seems to do is chuck the
> baffle out.
Is the jetting stock and are you at sea level? If so, then you need to
richen the pilot jet and main jet. What is your jetting right now? Look
at the numbers on the jets when you pull em out.
>
> Aside from getting a Mikuni carb ($$$) are there any other options for
> improving the performance of the original carb?
The Keihen works well enough when you get it jetted right and its easy
to jet (at least for me).
What about air filter
> mods, opening up the airbox etc?
No, don't do that, you will ruin the low end snap and not gain anything
else exept a dirty air filter. Except remove the splash guard if its
still in.
What about using a bell or "trumpet" on
> the intake from the airbox to the carby, similar to a road bike - would
> this make it run more smoothly?
Don't do that unless you like doing topends every weekend. Keep the
airfilter stock or go to a White Power filter (no, has nothing to do
with David Duke). XR motors last forever in this state of tune.
>
> Any advice and anecdotes are welcome.
I have no anecdotes, antidotes, or asymptotes right now. Sorry!
richard...