Can Any one tell me the standard Tire size for XR250R (1999) JDM,Front and Rear
Plus im thinking of putting a new Chain Sprocket set so i also want to know the standard stock sprocket sizes
If i go for a O-Ring Chain will i be not able to take out 9shorten0 the chain?
With the WISECO piston and ring set dose it need any other parts to be replaced...?9since its liter than the normal piston)
and i need the input on these...specially the part "GRINDING THE WELDED HEADER INLET"
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MY MODIFICATIONS TO A 2000 MODEL HONDA XR400R
(Revised: Nov 25, 2000)
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Stock Carb Specs
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Main 142, Pilot #52, Needle Clip in 3rd groove. Right off the
showroom floor, mine ran fine, but definitely on the rich side.
Removing the airbox snorkel without re-jetting, however, made
it run lean and overheat.
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RELIEVING THE 2000 HONDA XR400R MUFFLER BAFFLE
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(This is a very simple procedure, and one that can be almost
as easily reversed. Best of all, though... it works.)
After carefully examining the stock baffle/spark arrestor,
and running some flow numbers for the different areas
involved with the numerous plates and baffles (both in the
muffler and on the baffle insert), I've come to the
conclusion that the primary restriction to exhaust flow is
the small final outlet, which has an i.d. (inner diameter)
of only 20mm. Without removing the baffle insert from the
muffler, examine the exhaust tip. Notice the actual outlet,
which measures 20mm i.d. (approx. 0.787"). Around this is
a larger 'bright finish' ring which appears to have no real
function, but may be to help prevent the rider from coming
into contact with the actual outlet, which probably runs
hotter. Down in between the 20mm outlet and the bright-finish
outer ring, there is room to drill 1/4" holes into the baffle
to provide additional exhaust flow area. Holes drilled in
this area will be 'inside' the spark arrestor screen, by the
way, so the spark arrestor function is maintained.
On my baffle insert, the area to be drilled is large enough
to accept a 1/4" drill, but there's a benefit to using a #2
drill bit (0.21") (or maybe a 7/32" bit) which I'll explain
a little later on.
Since the stock 20mm (0.787") outlet provides a flow area
of only 0.4862 sq.in., and a 0.21" hole has a flow area of
0.0346 sq. in., each 0.21' hole adds 7.1% more flow area.
Just three such holes will increase the exhaust flow area
by over 21%, and four will increase it by over 28%.
First I ran the engine with the undrilled baffle, to get an
up-close feel for the sound level at idle, and while revving
the engine. After drilling one hole, I could barely hear any
difference. After drilling a second hole, I could hear the
difference, but it was slight. The third hole made a bigger
difference, but still not objectionaably loud. The fourth
hole made it just a little louder than I was willing to accept,
adding a definite bark to the exhaust note. Since I had use a
#2 drill bit, which is approx 0.21" in diameter (it's supposed
to be 0.221"), I was able to plug the 4th hole very simply by
screwing in a 1/4x28 set screw, which I woudn't be able to do
had I drilled the holes with a 1/4" bit. This effectively
reverted back to having just three holes, and it also indicates
that I can plug them all with 1/4x28 set screws, to return to
the stock sound level if necessary. Come to think of it, I
guess you could say that this modification is "tunable" by
inserting or removing set-screws from numerous holes.
A brief test ride with stock jetting showed that the added three
holes gave the bike a cleaner and stronger throttle response,
probably because it runs rich when totally stock. It was now
running cleaner, so the added 21.3% flow area was beneficial,
and it had cost me nothing but a little time. It's also totally
reversible by plugging the holes with set-screws.
It is NOT necessary to remove the insert when drilling each hole.
The metal chips will fall either outside the muffler, or into the
screened area of the spark arrestor. Once you have drilled the
desired number of holes, you can then remove the insert and shake
out the tiny pieces if you so desire. If you don't, they will
eventually fly out the exhaust outlet anyway, since the spark
arrestor screen prevents them from falling down inside the main
muffler.
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GRINDING THE WELDED HEADER INLET
---------------------------------
I'd read about the header inlets being partially shut off by the
welding that builds up when welding the 1" i.d. header pipes to
the clamping flanges, so I examined mine. Simply loosen the
clamp bolt where the header pipes assembly slides into the
muffler, and then loosen and remove the four nuts (two per pipe)
where the headers are clamped to the head. The muffler bolt and
all four clamp nuts accept a 12mm socket. Then the header pipes
assembly slides forward and into your hands.
On mine, a 2000 model, the built-up welded area in each pipe was
terrible! The remaining opening measured a rough 0.75", leaving
a flow area of only 0.44 sq.in. A 1" i.d. pipe has a flow area
of 0.78 sq.in, so the welding left only 58% of that! I started
grinding down the built-up welds using small grinding stones in
my Dremel Moto-tool, but that was too slow. I went to the hardware
store and bought some inexpensive coarse grinding stones to fit my
3/8" drill, and one 1" ball stone for finishing. I spent over two
hours grinding away. As a "size guide", I chose an 18mm socket that
has an outer diameter of 0.944" (different brands will vary in size,
of course). Once the 18mm socket would slide into the header pipe,
I quit, not wanting to remove too much of the weld, and weaken the
joint. I then used the 1" ball grinding stone to finish up. Since
the stone itself wears away faster than the weld material, I ground
a little on each pipe, going back and forth between the two, until
enough of the stone wore away to fit into the opening. This final
touch didn't really make either opening larger, but it did make
them both about the same size and shape.
Since I started with a 0.75" opening, which had a flow area of
only 0.44 sq.in., and finished with a 0.944" opening, which has
a flow area of 0.670 sq.in., I achieved a gain of more than 52.5%.
In one afternoon I significantly improved the flow characteristics
of the stock exhaust system, and my total investment was under $10
(for some cheap grinding stones and one 1/4x28 set screw). I
already had the 3/8" electric drill and #2 drill bit.
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AIR INTAKE SYSTEM
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I removed the air box snorkel, and then used a scrap of aluminum
window screen to cover the opening to keep out trash and clumps
of mud. I then removed the stock air filter and support, the latter
of which includes the backfire screen. Noting that the backfire
screen consists of two layers of screen, between which are trapped
two more layers (actually a flattened screen 'tube'), I carefully
cut away only the outer layer of screen, and removed the trapped
inner piece, leaving only one, the inner layer, of the original
four-layers of screen. I happen to like foam air filters, so I'm
sticking with the stock filter for now. (I later bought a TwinAir
filter, but with the backfire screen modified, I see no performance
difference between the TwinAir and the stock air filter. If I
were using a louder and more free-flowing exhaust, perhaps the
TwinAir filter would make a difference.)
NOTE: Cutting the metal screen is a chore, and it's difficult to
get rid of every tiny little piece of wire (from the screen) you
cut, so I no longer recommend cutting the stock backfire screen.
Intsead, buy a UniFilter air filter for the XR400R. It comes
with a screenless air filter support, and a less restrictive air
filter.
Despite what I read elsewhere, it is NOT necessary to move or
remove the subframe to remove the carburetor! After removing the
seat and gas tank, I simply loosened the two clamps holding the
carb to the airbox duct and intake manifold, then loosened and
removed the three bolts holding the intake manifold to the head.
By turning the intake manifold a little CCW first, the carb and
intake manifold then slide easily out the left side. After
removing the carb from the intake manifold, I examined the
composite rubber & plastic intake manifold. I do not think it
was necessary, nor do I think I gained anything from it, but
I used my Dremel Moto-tool with a medium size sanding drum to
clean up the few ridges found inside. Just couldn't resist!
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JETTING CHANGES REQUIRED
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After two days of trial and error jetting (and a few hours more
since then), I came to find that the exact same jetting recommended
by CYCLE NEWS (several years ago) worked best. I'm using a 160 main
jet, a #60 pilot jet, and the triple-tapered carb needle that comes
standard in the 1998 and later XR400R's, with the needle clip in the
stock (3rd groove) position. My altitude is approx 700' above sea
level, and I ride regularly up to 3200', where it still seems to
work just fine. I've also replaced the 15t drive sprocket with a 14t.
For the terrain where I ride, the stock gearing is a bit too high.
Depending on your particular machine, you might prefer a 158 main
jet is using a stock or modified stock exhaust. If using a louder
and nmore free flowing exhaust pipe, or the 1996-97 spark arrestor
without the muffler insert, you'll want to use either a 160 or 162
main jet.
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RESULTS
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How my XR400R might compare to a differently modified version, I
don't know. All I do know is that it easily pulls away from an
unmodified 1999 model, and that I am able to pull up the front
wheel at will in any of the first 3 gears. It is a little louder
than stock, but not as loud as a KLX300 with its muffler tip
removed, and it is nowhere near as loud as an XR or WR 400 with
the muffler insert removed altogether. It's more than I need for
woods riding, but without being 'difficult' to ride.
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XR400R Spark Arrestor/Muffler Note
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The 1996/97 XR400R has a two-piece exhaust pipe insert. The
removable spark arrestor has a removable muffler insert. With the
muffler insert in place, the exhaust is very quiet and very
restricted. With the muffler insert removed, the spark arrestor
alone has an open outlet nearly 1.5" in diameter, so it makes
really good power, but is also pretty loud. The 1998/01 spark
arrestor insert has the small 0.787" outlet which serves as the
combined spark arrestor and muffler, all in one piece. It has more
restriction than the 1996/97 spark arrestor alone, but more
restriction than the 1996/97 spark arrestor with the muffler insert.
Both of the two different spark arrestors fit all years of the
XR400R's exhaust pipe (three small bolts).
Gordon Banks
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