|TTR 125 needed Info
Written by Donkeyjyna
from PA_Kevin TT Moderator
this is used without permission, I am seeking permission, but it was so good I
had to post it.
For any "TTR Old Timers": During the format change (05/16/04) I copied this
posting by Donkey and saved it on my PC. During the format change, this ENTIRE
posting disappeared. Hence a very slight change in this post: my name appears as
the poster vice Donkey who gets ABSOLUTE 100% credit for this!!!!
1. Stock carb jetting
110-120 main, (depending on mods)
The needle works best in the stock position, or middle clip.
Jets can be found here: http://www.sudco.com/ The mains are the N100.604 Large
Round Type, and pilots are the VM28/486 Type.
You can order the correct TTR125 jets right from the Thumpertalk marketplace.
Large round type Mikuni main jets (N100.604)
107.5 TT part #MK-183
110.0 TT part #MK-184
112.5 TT part #MK-185
115.0 TT part #MK-186
117.5 TT part #MK-187
120.0 TT part #MK-188
VM28/486 Pilot Jets
17.5 TT part #MK-031
20.0 TT part #MK-032
They're $1.93 each
Here's a link to a detail drawing of the pilot and main jets in the carb of a
2002 TT-R125L. Bear in mind this bike is a California model:
TT-R125L Pilot & Main Jets
2. Airbox Mod
Consists of removing the snorkle/plug from the top of the airbox and removing
the screen from behind the filter. Every TTR should have this performed
immediately upon delivery. Even more air flow can be achieved by cutting out the
entire top section of the box and adding a high flow aftermarket air filter.
This will require a richer pilot and main jet and tuning of the fuel screw to
get the best response and power. However, it should be taken into consideration
that the more extensive airbox mods may not be a good idea for someone who rides
in extreme conditions often. With the top completely removed water or sand could
easily get into the box and cause the bike to run poorly.
3. Flywheel mod
Basically, the flywheel creates rotating mass in your engine, keeping it
spinning when you let off the gas. The "flywheel mod" involves machining
material (up to 18oz.) from the flywheel, making it lighter, and in effect,
allowing your engine to rev faster, or "spin up" quicker. The drawback is that
the engine is easier to stall. Some internet companies charge over $100 for this
service, but most local machine shops will usually do it for as little as $25.
Overall opinion is that this is a very worthwhile mod for the money, but is
better left to the more experienced riders.
4. BBR frame cradle compliancy
The BBR frame cradle is an essential item for the TTR. It adds much needed
rigidity to the frame and also protects the engine, while at the same time,
being very light weight.
These pipes have been proven to fit well with the BBR frame cradle:
BBR (of course)
Pipes that have been proven not to fit:
Stock pipe (oddly enough)
5. Handlebars and Handguards
The stockers are weak, but there are many aftermarket bars to choose from in all
shapes and sizes. However, most every rider prefers a slightly different setup,
so you need to put some thought into how you like to feel and position yourself
on the bike beforehand. The best thing to do is measure the stockers up, and
compare those #'s to what's listed on the Renthal/TAG/ProTaper web sites. That
way you can get a good idea of what you want, and what to expect. Oversized,
1-1/8" bars are great, but will require adapters or a new triple clamp. They
damp out most of the vibration and resist bending like you wouldn't believe. Not
to mention the fact that they look cool. But the extra thick 7/8" bars aren't
bad either, and will bolt right up with no extra parts to purchase. You can buy
your handlebars from a million different places, but look around for the best
deals. TAG, Pro Taper, and Renthal all make oversized billet adapters for around
$75, but remember, they raise the bar height 3/4 of an inch themselves, so keep
that in mind when figuring out which bend you want. Triple clamps with oversized
mounts can be found here: http://www.rswracing.com/ here: http://www.precision-racing-components.com/
and here: http://www.bbrmotorsports.com/Home.htm At prices from $100-200. I
suggest the RSW triple clamp. Ron also makes a very nice and highly effective
billet fork brace, which at $70, is probably the best deal on a performance
accessory that you'll find anywhere.
The Acerbis Rally Pro's are the best thing goin' at $75. But reguardless of
brand, the key is the sturdy reinforcing aluminum backbone. The plastic
brushguards do little to protect your hands or the levers during a get off. If
you are using oversized bars, you'll also need adapters for the handguards. Of
course, all the major players can supply you with their version, and all seem to
work well. With good bars and handguards your bike becomes almost indestructable.
No more bent or broken levers. And no more fingers smashed between the bar and
6. Other Basic Mods
Sprocket changes are sometimes necessary. For more top speed go with a larger
front sprocket or smaller rear. For more low end power do the opposite, smaller
front or larger rear. The 14 and 15 tooth front sprockets work well and are
readily available from Sprocket Specialists here: http://www.motorcyclesprockets.com/html/main.shtml
They also have a wide selection of much lighter aluminum rear sprockets.
An actual chain guide is another well advised security mearsure for the TTR.
There are many on the market, more popular versions being sold by BBR and PRC.
A stainless steel brake line is one of the best $$$ value mods available, and
adds great feel and extra power to the TTR's front disc. I prefer Goodridge
lines and have used them on all my bikes for a long time with great success, but
there are several other brands available. Galfer, Speigler, Russell, ect... Most
any manufacturer can make a custom line in any length you need with all the
hardware in any configuration you want. Prices range from $50-90. Keep in mind,
the stock rubber lines are supposed to be replaced every two to three years.
Stainless lines are good for at least 10.
Brake pads can also be upgraded. The stock pads offer decent feel and power, but
they overheat and fade quickly with the small rotor. Again, there are several
brands on the market to choose from, and many times it comes down to personal
7. YZ carb mod
The last generation of round slide carbs from the YZ80 make great improvements
to the TTR for little $$$ and fit right up with no modification. (2.5mm can be
milled off the engine side for a perfect fit, but is not necessary.) They are
particular about jetting, but make very good power. Look on Ebay and in junk
yards for a clean model from 1982 to 2001. They are all basically the same and
can be had for as little as $20. Strait from a YZ, they will be very rich on top
and bottom, and lean in the middle on the TTR. A good place to start with
rejetting is a 20-22.5 pilot and 140-150 main. The best needle is still
undecided, but any of the richest Mikuni 4 or 5 series needles could work. (The
stock YZ needle seems to fall just on the rich side of the middle of the charts
in the Mikuni catalouges.) Slide sizes could also be changed. The YZ's slide is
a #3. A #2 or even #1.5 could work well? Many folks have opt'ed to replace the
stock O-0 needle jet with a P-4 size and keep the YZ needle. This seems to work
well too. But remember, jetting will be different on nearly everyone's bike, so
what works great for one, may not work as well for another. These are all just
generalized places to start. Getting your bike finely tuned is half the fun. But
overall, the YZ80 carb mod is very much worthwhile for the added power and
response. It also enables the use of a pod filter, which is impossible with the
stock carb. All necessary jet's and needles can be found here: http://www.sudco.com/
and here: http://www.mikunioz.com/
8. Suspension mods
The best money you'll ever spend on any motorcycle is in getting the suspension
dialed in. Not only will it enable you to go much faster, but you'll be doing it
with less effort and more direct control of your bike. There are several routes
that can be taken to upgrade the TTR's stock suspension. The easiest, and most
common thing to do is add heavier aftermarket springs front and rear, thicker
oil to the stock forks (10-15wt.), and purchase stronger billet triple clamps
and a fork brace.
Those mods alone make terrific improvements over stock, but can still fall short
for many larger and/or more aggressive riders. The ultimate suspension upgrade
for the TTR125 is to replace the entire front end with an inverted forked, and
much more rigid, '93-present YZ80/85 or KX80/85 front end. You'll need to change the
springs to match the heavier bike and there's some simple adaptation required,
but a kit for the YZ-TTR swap can be found here:
The YZ forks are much longer than the stock forks and can be shortened to
maintain the stock ride height or a BBR swingarm can be purchased to raise the
rear 1.5". They will also need to be matched up with a shock in the rear that
can equal their performance level. The Works Performance shock seems to be the
popular choice, but the newer generation TTR shocks with the remote reservoir can be
rebuilt with a good deal of success.
9. Motard Conversion
The most common modification is to lace wider aftermarket 17 inch rims, such as
Excel or Sun, to the stock hubs with heavy duty spokes. They are available here:
http://www.buchananspokes.com / and here:
All year model TTR's with a stock or YZ/KX front end can run either a 2.5/17" or
2.75/17" front rim. The 2.5" is the preferred and standard 125GP size, but
restricts your tire choices to full blown race tires if you want the proper
profile to be maintained. The 2.75" rim is wider than necessary, but allows the
more common 110/60 size sportbike front tires to be used without distorting
their intended profile. Whether you are able to use the entire tire surface with
that size has yet to be proven, though.
All '02 and older TTR's, and newer standard and "L" models without the aluminum
swingarm, are restricted to a 2.75/17" rear rim with a 110/70 tire. The '03 and
newer "LE" models with the wider aluminum swingarm have the choice between the
2.75/17", or the preferred 125GP sized 3.5/17", rear rims. The 3.5" wide rear rim
allows you to run tires up to a 120/70 without any issues. 120/70 is the most
common size of sportbike front tire, and they work great as rears if turned
backwards. High performance street tires, DOT race tires, and full blown slicks
are all available.
The 125GP setup (2.5"f, 3.5"r) is more restrictive as to front tire choice, but
offers the best performing tires and sizes, and easily available rears in the
most common size of all. Only three manufacturers make tires for the 125GP bikes,
Michelin, Bridgestone and Dunlop, but they are all very good. A set at retail is
expensive though. $200-300 front and rear. You do have the option of slicks or
rains, and Dunlop and Michelin offer two compound choices. Much cheaper
take-offs are out there to be had too. The Dunlops feel great and last a very
long time, but are a harder compound rated for higher temps, so they take a
while to "come on".. They also have a very stiff carcass so they tend to chatter
more than slide sometimes. The Bridgestones and rated for a much lower optimum
operating temp, so they heat up faster and work better at the lower temps that
the TTR is likely to see. However, they are softer and don't last nearly as long
as the Dunlops. They are cheaper though. The Michelin front tire doesn't suit my
riding style, but I do like their rear tire.
The 2.75" setup has it's advantages in the fact that many decent tires are
readily available, and can be had for cheap. However, it doesn't offer the
all-out performance potential of the GP setup with slicks and a fatter rear. The
steering is a little slower, and the response isn't as good with the wider
tires. But there's plenty of grip to be had with good street tires. It also
takes a lot more suspension to deal with the super grip of the slicks. Street
tires may be just as fast, if not faster on some bikes.
10. Extreme Tuning
Of course, there are those that will never be satisfied with the amount of power
their bike makes. Thankfully, I'm one of you.
The sickest power mods for the TTR begin with the camshaft. BBR, Powroll, PRC,
and HotCam all make excellent cams for the TTR. I love my HotCam and Wiseco
makes a drop in 11:1 high compression piston that works great with it.
Next up would be porting, polishing, and head and valve work. In this area it's
really all about who you know and how good they are. I doubt you'll pry any
secrets from the real competitors about the specifics here. Just have to find
out for yourself. But the TTR's do have a good bit of power in there.
Big bore. What else needs to be said? There are several 150 kits on the market,
and Powroll even offers the mac-daddy 170 stroker. And if you can't find enough
juice for your TTR in 170ville then you've got the wrong idea entirely.
BBR - www.bbrmotorsports.com/Home.htm
PRC - www.precision-racing-components.com/
RSW Racing - www.rswracing.com
Sudco - www.sudco.com
|I think this is from Kevin of ThumperTalk.com
I thought it would idle without the choke. But with when the choke was off it
would not idle. But the opposite happened with the choke.
Is there any particular reason for this?
Your carb meters the fuel to your engine. The carb has three different sub
Pilot Jetting - for up to 1/4 throttle position
Needle Jetting - 1/4 > 3/4 throttle position
Main Jetting - 3/4 > full throttle
These jets allow a fixed amount of fuel, the needle allowing an "operating band"
of fuel metering.
To alter the amount of fuel, you can either increase or decrease the orifice
(the hole in the jet). This applies to your pilot and main jet.
The needle jet is actually a needle. The fuel first passes through the main jet,
then the needle limits the fuel flow (kinda like putting your pinky finger into
a garden hose. Water still comes out, just not as much).
The reason your bike won't idle:
The Fuel Screw is mis-labeled in the Yamaha manual. It is labeled as an "Air
Screw". This is 100% backwards. Air screws are on two stroke carbs. The last I
checked, this carb has been on this 4 stroke engine.
The fuel screw allows more fuel through the pilot circuit. This very definitely
affects low speed operation. To allow more fuel flow or richen up the bottom
end, the fuel screw is turned counter-clockwise (or turned OUT). This IS
richening up the bottom end.
To lean it out, the fuel screw must be turned clockwise (or turned in). The
problem with this low speed/idle jetting is it is too lean. The only time I
think you would turn it in is if you decide to ride your TTR into the Rockie
Mountains, where bikes are starving for air, which ain't there!
First, your pilot jet is absolutely too small. You need to go up in size to a
17.5. The fuel screw on your carb allows a VARIABLE amount of fuel to pass
through the pilot jet. This fuel screw WILL ABSOLUTELY affect your idle. The
fuel screw has a spring behind it that allows you to turn it without it falling
out of your carb. Turning it in REDUCES the amount of fuel (leaning the fuel/air
mixture) and conversely turning it out INCREASES the amount of fuel (richening
the fuel/air mixture). The bike IS starving for fuel at idle because the pilot
jet is too small. Regardless of the fuel screw position, your bike NEEDS MORE
FUEL. If you end up turning your fuel screw out 3 turns or more, your pilot jet
IS TOO SMALL.
The needle jet can be changed as well, or raised or lowered. So far, I have not
seen any recommendations to swap out needles. Needles vary in diameter, AND
taper in size, i.e. the tip of the needle is skinnier than the diameter half way
up the needle. So as the needle is being pulled up, the needle gets skinnier.
This allows MORE fuel as the needle is raised up via the throttle cable.
There is a clip on the needle that allows you to raise or lower the needle,
effectively changing the amount of fuel flowing in this 1/4 > 3/4 throttle
position. So, if you move the clip down, this effectively raises the needle.
Since the needle is now higher in the carb, and we know the needle is skinnier
at the bottom, MORE fuel will pass through in the midrange than before you moved
As for swapping out the needle, the skinnier the needle, the more fuel allowed
into your engine.
At 3/4 throttle and higher, the ONLY thing metering fuel is the main jet. If
your bike has problems at wide open throttle, the main jet is your culprit
(unless it's your ignition...???). A larger main allows more fuel.
When you modify your bike, i.e. cut your airbox lid, install a high air flow
airfilter, you are changing the amount of air into the engine.
When you install an aftermarket exhaust pipe, more air (exhaust) is coming out
of your engine.
In BOTH of these conditions, you MUST increase the fuel going to your engine to
offset the air going into (or out of) your engine.
Moving more air means you have to move more fuel.
Elevation & Weather Changes
When there is a change in the weather or riding elevation, the amount of Oxygen
or moisture will be the culprit. At higher elevations, there is less O2
available. You will need to jet lean to decrease the amount of fuel to
compenstae for the lower O2.
If it is humid, there is MORE water in the air, you MAY have to jet lean.
In the winter, bikes run lean. Because of the lower temps and humidity, there is
more O2 due to density changes. Your bike will run lean, and you will benefit w/
I hope this helps you understand carbs better.