WARNING!!!
Any or all of the modifications listed below may cause permanent
and irreversible damage to you or your motorcycle, and/or may
result in a motorcycle that is unsafe and dangerous to ride.
Neither my self, my heirs, nor my associates are responsible for
any damages or injuries that occur as a result of the following
modifications and suggestions.
MAKE THESE CHANGES
AT YOUR OWN RISK!!!
Carburetor
Bob Burkart recommended the carburetor modification. He says that
it helps with the transition from idle to higher throttle
settings and helps with the Pinging problem that 350s seem to
have when you shut the throttle down. It involves increasing the
throttle slide cutaway, and changing to a larger pilot jet, or
drilling the present pilot jet. The larger pilot jet enriches the
mixture across the entire range of throttle operation. But it
makes the mixture far to rich at idle. Increasing the throttle
slider cutaway leans the mixture at idle only and so compensates
for the richer pilot jet. This is for the stock carburetor only.
Be sure you check to see if this modification hasn't already been
done before you change anything or spend any money. To check
remove the slider and look at the bottom of the slider and the
bottom edge of the cutaway. If the bottom of the slider has a 25
stamped on it and the bottom edge of the cutaway still has chrome
on it then the mod hasn't been done yet. If the slider is a 35 or
the bottom edge of the cutaway is brass colored then it's likely
that this modification has already been done.
You will need a couple of sheets each of WetOrDry sandpaper in
the following weights; 180, 400, 600, a FLAT surface for
grinding. The best thing that I've found for a Flat surface is a
piece of glass. A piece of thick Mirror, about 12" x
12" would be ideal. It seems that mirror glass has fewer
defects than window glass.
Remove the carburetor slider. Looking at the slide with the
cutaway facing you make a mark that 1mm up from the bottom front
edge of the cutaway on the center line of the slider. After you
make that mark then measure down from the top of the slider to
the mark and record that distance. If you lose the mark during
the grinding process you will use that distance to figure out
when to stop grinding.
Make some soapy water using dish detergent. Take a piece of 180
grit WetOrDry wet it down real good with the soapy water and
place it, cutting face up, on the glass, which should also be on
a solid flat surface. If you wet the glass it will tend to stick
to whatever flat clean surface you put it on and make the
grinding easier. Being extremely careful not to alter the point
where the cutaway arc intersects the side of the slider, sand the
slider down to your 1mm mark. Keeping the sandpaper soaked with
soapy water will ease the cutting and speed the process. As you
get closer to your mark go to progressively finer grits of sand
paper finishing with the 600. When finished you should have a
cutaway that matches the factory in finish and sharpness at the
edges. Clean, dry and reinstall the slider. Test the motorcycle.
It should run but not Idle.
If you can get it to Idle with Air Jet Screw between 1 and 2 1/2
turns then stop. You're finished. If the airscrew adjusts greater
than 2 1/2 turns then you need the next smaller pilot jet. If the
adjustment of the airscrew is less than 1 turn you need the next
larger pilot jet or you need to drill the one you have.
If you want to drill out the Pilot jet I would recommend going to
a Good Welding supply store and get a Tip Drill set. This should
include a set of small drills including a .015(#?),
.018"(#77) and .020"(#77) and a drill vice. This size
of drill bits are very fragile and may be too small to fit in a
regular drill, so the drill vice included in the tip drill set
makes the whole process easier and you get a lot of other really
small drills. The drills will be used to drill out the pilot jet.
DO NOT use these drills to drill Main jets!! The sizing of the
holes in the main jets is far more precise that can be achieved
with these drills.
Remove the pilot jet. Starting with the smallest drill in the set
try to fit it into the jet. If it fits then move up a size until
you find the size that won't fit. Using that one to drill out the
jet. Reinstall the Pilot Jet and do the Idle adjustment again.
Again if you can get it to Idle with Air Jet Screw between 1 and
2 1/2 turns then stop. You're finished. If the adjustment of the
airscrew is less than 1 turn remove the pilot jet and drill it
out with the next larger drill and repeat the test. If the air
screw adjusts greater than 2 1/2 turns then you have over drilled
this jet and now to buy a new pilot jet.
I had a 36 pilot jet as an original and then went to a 32, which
was too small. So I drilled it out with a .015 tip drill and it
works perfect
Cylinder Head
The TY-350 often pings when it's warm. Part of the reason is that
the Squish Band is poorly designed. A cheap remedy, is to remove
the head gasket. Remove the head, and the studs that hold the
head to the cylinder. Put some valve-grinding compound on the
gasket mating surfaces, then lap the head to the cylinder. Remove
all of the valve-grinding compound, and clean the surfaces with
brake cleaner, acetone, etc. You need a clean dry surface where
the cylinder and head meet. Reinstall the studs, and put a thin
layer of high temperature silicone gasket sealer on the mating
surfaces and reinstall the head. This will reduce the squish band
clearance from about 0.080 to 0.040 inch. Which works a lot
better, and will reduce pinging. To find out why, you will have
to study two-stroke theory.
FLYWHEEL
If you remove the flywheel weight from the flywheel the
motorcycle will hit harder, quicker and will wind down from high
rpm quicker. It will be more responsive and have less run on
(same thing different words). It makes the 350 feel frisker. The
downsides are that it's an all or nothing procedure, it removes
all of the extra weight and is irreversible, and also the motor
is less forgiving of improper clutch technique at low rpm.
A considerable amount of the flywheel effect comes from a metal
band that is apparently heat shrunk on the flywheel. There are
two ways to remove the weight. They both require you to cut
across the wide part of the weight down to the flywheel whereupon
the weight will separate from the flywheel. The difference
between the methods described, is that one I've tried and the
other I haven't HO HO!
In accordance with the maintenance manual, remove the skidpan,
and the flywheel cover. Find the timing mark stamped on the
flywheel weight and transfer that mark to the flywheel. Make the
new mark permanent but DO NOT HIT THE FLYWHEEL WITH A HAMMER
TRYING TO MAKE THE NEW MARK. Impact will tend to dislodge the
flywheel on the crankshaft, bend the crankshaft, dislodge the
crankshaft bearings, break the crankcase seal and demagnetize the
Ignition and lighting magnets in the flywheel. So, it might not
be a good idea to use a hammer and a chisel to make a new mark.
Try scratching a mark with a sharp tool; just don't make the
scratch to deep for reasons that will be explained below.
Then, if you can, fit a SHARP hacksaw blade between the outer
edge of the flywheel weight and the case, then start sawing.
REMEMBER, take your time and try to stay square with the wide
part of the band. DO NOT CUT INTO THE FLYWHEEL!!! If you nick the
flywheel it will provide a place for a stress crack to start
(same thing for a deep scratch). I put about a .003 in nick in
mine and I don't anticipate any problems but you do want to be
careful not to let the hacksaw cut into the flywheel.
Also try to control the metal chips that come from the sawing.
Temporally wrap the flywheel in Saran wrap to prevent chips from
entering the flywheel. Since the Yamaha has no moving parts in
the flywheel section, a few chips may not cause any problems, but
good practice dictates that ANY metal shavings are a no no. The
magnets, that are a part of the flywheel, will attract the chips,
so try placing the hacksaw blade so the cut takes place on the
pull stroke, that way the chips will tend to fall out of the
flywheel area.
The above method will require more time to cut the band than the
one that I used but it doesn't require any special tools, just
lots of care and patience
The method that I used was pretty much the same except I removed
the flywheel and used a metal cutting band saw to cut the band.
If you remove the flywheel and put it in a vise, it will take
less time to cut the weight off, it will be easier to remove the
metal filings, and easier to transfer the timing mark from the
weight to the flywheel. You'll need a flywheel puller, a flywheel
holding tool, a 19mm (3/4" will work) thin wall socket, and
a torque wrench.
The flywheel puller is a special tool that you should be able to
get at almost any Motorcycle Shop, or the Trials Shop.
The flywheel holder keeps the flywheel from turning when you
remove and install the flywheel nut. It will be harder to find.
If you can't find one, try putting the bike in gear and holding
the rear brake. Try a higher gear first. If that doesn't work try
wrapping a tie down strap around the flywheel and hook it to the
foot peg to hold the flywheel. Wrap it so that as the flywheel
turns it tightens the strap.
A thin wall 19mm socket may also be hard to find but cheap
3/4" sockets are generally thin wall. I used a Sears
Craftsman 3/4", 3/8" drive, #44337 with a 3/8" to
1/2" adapter and it worked real well.
Shock extension
The Stock Yamaha suspension is not very progressive, and the bike
has an awful lot of rake for a trials bike. One cheap and easy
way to fix this is to extend the length of the stock shock. If
you extend the stock length 0.31" then it moves position of
the shock actuation on the arc of the transfer link. This
increases the progressivity of the suspension. It also raises the
rear of the bike, which increases ground clearance, and decreases
the rake. The disadvantage is that it also raises the rear fender
and seat height.
Remove the bottom shock attachment from the shock and Carefully
grind or cut off the U-bracket at the weld. Fabricate another
U-bracket with the holes extended 0.31". Weld it on to the
attachment, reassemble and reinstall. You will notice the
difference.
Shock Preload
I have heard that preload should be set so that the bike sags
1/2" under its own weight. If you extend the shock you might
need to increase the preload past what the maximum stock setting
is. This can be done by cutting a groove be cut in the body of
the shock. Remove the shock and the spring and adjusting hardware
from the shock body. Then take the shock to a machine shop and
cut a groove identical to the one already cut into the shock
body, 12mm closer to the shock rod. This will place the lowest
possible setting, one setting above the highest stock setting.
WARNING THE SHOCK IS PRESSURIZED! INJURY OR DEATH
COULD OCCUR FROM FOLLOWING THE ABOVE PROCEDURE. WARN THE
MACHINIST WHO WILL BE WORKING ON THE SHOCK !!!!!!
Foot Peg Mounts
The foot pegs were lowered 1.75". I took measurements from
the center of the seat mount bracket hole, the center of the
swing arm pivot bolt and the center of the foot peg spring hole.
The drawing included shows the new measurements. Before you cut
the pegs off double check these measurements to see if they will
result in the location that you want. There could be differences
between frames, which may affect the accuracy of the above
distances. . Remember to check the angle of the mount before
removing it and be prepared to be able to duplicate that angle
when you jig it up. The foot peg mount angle is relatively
critical.
Remove the foot pegs and hardware. Remove rear brake lever and
hardware. Cut the triangular foot peg brackets off of the frame.
Make the cut just on the peg side of the welds. I used a die
grinder with a cutoff wheel. WARNING Ensure that you DO NOT CUT
INTO THE FRAME when you remove the Bracket. After you have
removed the brackets grind off the old welds down to the profile
of the frame tube.
You will need to make a spacer to go between the frame and the
old bracket. Jig the old bracket in it's new location and then
using cardboard slightly stiffer than a 3X5 card make a template
that fills the gap between the old bracket and the frame. You
will need 4 templates, inside and outside each peg both sides.
I made my templates so that they were slightly longer than the
distance that the template contacts the frame and bracket. That
way when I made the metal spacer plate I was able to bend the
tops and bottoms of the plate over so that when welding them to
the frame the inners and outers joined at the tops and bottoms.
Fabricating the brackets will require some patience. Take your
time here because a good fit will make the new bracket much
stronger. Weld the spacers on the frame and weld the footpeg
brackets to the spacers. Clean up the welds and paint.
With the Pegs lowered 1.75" the Center of gravity of the
bike is lowered which results in much more controllability, and
gives the rider a more stand up stance. The down side is that
your feet are closer to the bottom of the skidpan and I've caught
my toes on some obstacles. Also the brake cable will rub along
the swing arm. This may affect braking slightly, but I haven't
noticed it.
NOTE: Some folks claim that the front end of the TY-350 is too
light. If you lower the foot pegs, you might want to consider
moving them forward as well. Moving the pegs forward 1" will
transfer more of your body weight on to the front wheel. The
modification may also be easier because you might not have to
make a spacer, or at least the spacer will be smaller. I rode a
TY250 in Oklahoma where the guy had just cut the peg brackets off
the frame and then slid them down the frame tube to where he
wanted them and rewelded them back on the frame. I don't know how
far forward this places the pegs. When I rode that bike, all I
noticed was how much easier the bike was to balance and how
stable it felt, so I was convinced that lowering the pegs was the
hot ticket. If I was to do it again I might consider moving the
pegs forward.
Throttle Spacer
The Throttle Spacer is a piece of plastic that fits in the cable
groove of the twist grip. Its purpose is to increase
progressively the throttle action. The stock twist grip is an
approximately a 3/8ths grip. This means that that it is about
3/8ths of a turn of the twist grip to go from closed throttle to
wide open. When you place this piece in the grip it changes it to
a progressive 1/4 grip. The first part of the turn is the same
rate as the 3/8ths, but from about 1/4 throttle and up the
throttle opens faster for each degree of twist. The result is a
fine throttle control at low throttle settings combined with the
ability to get to full throttle without having to move your hand
on the grip. Basically it makes the groove increase in diameter
as you turn the grip which pulls more cable quicker as you turn
the grip.
It's a piece of plumbing plastic. I think I made mine out of
5/8ths-inch schedule 40, the white stuff. Take a fine saw and cut
a small slice off the pipe so that it will fit in the cable
groove. Then split it in one place and file at the split
"B" to make a ramp for the throttle cable. The
thickness "C" could be adjusted to increase or decrease
the rate of change. Trim away the excess length to fit,
"A" install and test. I used 5-minute epoxy to glue it
to the twist grip. It made the install a bit more permanent.
Another way to do the same thing would be to tape a waxpaper dam
around the part of the twist grip where the throttle cable goes
and fill that area with J B weld (another epoxy material) and
then shape the semi hardened J B weld with a file to get the
right shape. Test some J B weld first to see how it works and
files.
Handlebars
I've shortened the bars to 31.5" and they work well for me.
When you shop for new ones look for bars that have the bends
close in to center. Then you will have more room to adjust the
location of the clutch and brake perches.
Clutch Arm
The stock clutch feel was too stiff for me to use the clutch with
one finger so I extended the length of the stock arm. The length
of the external clutch arm is 2.5". If you extend the clutch
arm don't just tack a piece on the end of the clutch arm on the
centerline of the existing piece. That will place the hole for
the cable too far away from the end of the cable itself. Instead,
with the clutch and cable adjusted properly, remove the cable end
from the clutch arm and swing the cable end toward the cylinder
until it is 2.5" from the center of the clutch arm pivot.
This will show you where to place the hole on the extension. As
you will see it has to be at an angle to the centerline of the
clutch arm.
Disk Brakes
I installed a disk brake on my TY-350 and one on my son's. They
both work better than the stock drum brake. I got most of my
setup from Bob Ginder of B&J Racing by trading a 1969 Greeves
for a Fantic front wheel, a Grimica master cylinder, a stainless
steel braided brake line, and an mounting bracket. Jesse's was
purchased from Mike McLaughlin. It included a 21" rim laced
to a ?????? hub, a brake hose, a Honda master, and a Honda single
puck slave.
I used the Honda master and hose with the B&J bracket, the
Fantic front wheel and a Honda Rebel slave on my 350. On Jesse's
I used the Grimica master, the stainless steel braided line, the
custom wheel and a Honda MB50 slave.
Here is the data that I gathered while looking for a Disc brake
setup. The information is incomplete because I stopped looking
when I traded the Greeves for the Yamaha Kit. The best
combination that I came up with before I stopped was as follows;
The Honda Master cylinder is the only one that I found that has
an 11mm bore. I don't know what it came from because it came with
the kit from Mike Mc.. The RX-50 master was listed because it is
the only one that I found with a 10mm bore other than a Grimeca.
The Honda Rebel Caliper was selected because of the way that it
mounts on the stock motorcycle. It and the MB50 caliper are
located on the rear side of the right slider. The Trials
installation mounts the caliper on the forward side of the left
slider. So you must look for a caliper that mounts on that side,
or on the rear of the right slider. Also the Rebel caliper has 2
pucks and a pad with a larger surface area. Although it is
heavier then the single puck calipers, I thought that the extra
weight would be offset by an anticipated increase in braking
effectiveness. The MB-50 caliper was my 2nd choice because it is
a single puck, and the pads have less surface area. Most
motocrossers have the brake on the rear of the left slider and so
are not desirable for a trials installation where dropping the
front wheel into a crevice might hit a caliper installed on the
back of the slider.
The choice of brackets was made based on ease of installation and
ability to return to stock brakes if necessary. The B&J
Racing Bracket had some fore and aft play, so I put some mold
release on my slider and filled the gap between the brake tab on
the slider and the bracket with epoxy filler. It seems to work
great, no slack or slop. I also had to make an adapter plate
between the bracket and the caliper because the B&J bracket
was made for a Grimeca or Brembo caliper. A Custom made bracket
could be more precise and require no adapter, but it would be
time consuming and probably cost more. Welding to the slider was
the last choice because of the potential problems with distortion
of the fork tube and metal compatibility in the welding process.
I didn't like the looks of the welded brackets that I've seen on
other TY-350s with disk brakes, which led me to believe that
there may be a welding problem with the aluminum of the sliders.
On the plus side, a welded bracket would give a positive and
lightweight attachment point.
After installing Disc brakes on Jesse's and my 350 I've decided
that it was well worth it. Both motorcycles' brakes are easier to
operate over a wider range of engagement. Neither release as well
as a factory disc brakes. There is a slight drag that I attribute
to the difference in precision between the installations.
The Jesse's has a Grimeca 10mm master and a MB-50 30.15mm slave.
10mm dia. = 78.5 sqmm
30.15 dia = 713.6 sqmm
ratio = 9.09/1
The mine has a Honda 11mm master and a Honda 2 puck 25.4mm ea.
slave.
11mm dia = 94.9 sqmm
25.4 dia = 506.5 sqmm
x 2 = 1013 sqmm
ratio = 10.7/1
The mine seems to be more progressive, powerful and precise than
the Jesse's brake. I think that's because mine has a larger pad
area and the fact that it is riding on a solid disc. Jesse's has
a smaller pad area and is riding on a heavily vented but larger
diameter disc.
Before I got the above parts, I did some looking around in an
attempt to put together a disk brake setup for the TY-350. The
list below was made by calling parts people and cross checking
numbers. I did not verify the accuracy of the information because
I was just in the initial stage of the process. It also shows the
KX-80 with 2 sizes of bearings. I believe that the parts man gave
me the bearings for 2 different variations of the KX-80, the one
with the 6300 bearings was the one that I selected because the
bearings from the TY-350 would (should) slip right in and ease
the installation. I never did get my hands on a Kawasaki rim to
verify the sizes. The RM-80 was my 2nd choice because of the
number of spokes would allow me to use the rim from the TY-350,
although it might require some welding and machining to fit the
proper size bearing.
I haven't done much to the front forks, but here it is. I cut the
tightly coiled end off of the spring. The remaining length was 13
inches. With that spring, I use a 6-inch preload spacer, made out
of conduit. I run 300cc of Dexron III transmission fluid in each
leg. Shortening the spring stiffens it, and the Dexron seems to
provide adequate dampening. For additional modifications contact
Chris Johnson <papazit@juno.com>, and/or Jon Stoodley
<stoodley@oknet1.net>, and thanks to both of them for their
help and advice.
All of this stuff is taken from letters I've written to friends,
or they have written me, and so some of it may sound odd. I have
edited parts of it to make it clearer but that's all if you have
any questions, feel free to contact me.
