2012 Ktm 50 Sx Mini
KTM 50 Bible
Ok heres a link to the KTM 50 Bible, it has every thing you need to know http://ktmtalk.com/index.php?showtopic=235643
Plug you need is NGK LR8B, apparently the air screw settings for these run from 1-4, more than 4 turns out need smaller pilot less than 1 bigger seems extreme but the mini's are different heres a right up that has all you need to know for jetting em, since I already told ya on the phone do ya self a favour and READ IT!
Have also included the pdf as there is references to images that I cant load in the right spot, cheers roddy..
Carburetor Jetting according to GrantsDad#25
For all of you who lift the rear of the bike and rev it to the moon to ?clear it out? on the
line, inspiring an industry of custom seat lift straps, this is for you. My $0.02 on jetting.
Jetting your bike properly is one of the most critical factors in making your engine
perform at it highest potential. Improper jetting can not only reduce the performance of
your engine, but it can also do serious damage. Following is a compellation of tips, tricks
and techniques I have learned through reading and trials.
Let?s cover the basics first:
Jetting the carb refers to making changes or manipulating the 4 main circuits in the carb
to tune the fuel and air mixture to achieve maximum performance in all RPM ranges.
These carburetors work based on throttle position and not RPM. The key is to match the
settings of the 4 circuits in the carb to the RPM of the engine at that throttle position and
maintain a smooth transition between circuits.
Rich and Lean:
Rich and lean terms refer to the air and fuel ratio and have nothing to do with the amount
or ratio of oil you are using. The ideal ratio of air to fuel for a 2-stroke engine is 12.5:1. A
rich mixture has an increased percentage of fuel and does not have sufficient air
(oxygen) to burn cleanly or completely. A lean mixture has an increased percentage of air
(oxygen) which can cause high combustion temperatures and damage. Buy adding more
premix oil, going from 40:1 to 32:1, actually makes the air fuel mixture leaner since there
is more oil and less fuel being mixed with the incoming air. Temperature, altitude and
humidity also affect the air fuel mixture, with temperature having the greatest affect.
Lower temperature causes molecules in the air to move more slowly, resulting in more
oxygen molecules per volume of air and causes a natural leaning of the mixture. The
reverse occurs for higher temperatures. Remember HIGH = RICH and LOW=LEAN.
High temperature air is less dense with oxygen, high altitude air is thinner or less dense
with oxygen and high humidity air is less dense with oxygen due to the increased amount
of water molecules. Low temperature, low altitude and low humidity all contribute to a
denser oxygen mixture per volume of air and will cause a leaner mixture at the engine.
These are the reasons for adjusting your jetting for different times of the year, part of the
country or even times of the day. Factory jetting is general, not ideal, since the
manufacturer ships to all areas of the world and all different environments.
Parts:
. This screw works in
conjunction with the pilot circuit to adjust the mixture of
either air or fuel. If the screw is on the engine or reed side of
the carb, Pro Sr 19mm carb, it is a fuel screw and will richen
the mixture when turned out and lean the mixture when
turned in. If the screw is on the air filter side of the carb, Pro
Jr 14mm carb, it is an air screw and will lean the mixture
when screwed out and richen the mixture when screwed in.
The mixture screw affects from idle to 1/8 throttle.
. The pilot jet provides fuel for the idle
circuit and mostly affects from 1/8 through 1/4 throttle. Pilot
jets are numbered based on the size of the hole through the
center. The larger the number, the larger the hole and the
more fuel that can pass through it. A 55 pilot will richen the
circuit more than a 45 pilot.
. The slide mainly affects from 1/8 to 1/2
throttle. The half-moon cutout on the air filter side of the
slide controls the amount and velocity of air passing through
the carb. Slides are sized based on the size of this cutout. A
50 slide has a larger cutout than a 40 slide and the 50 slide
will lean the mixture between 1/8 and 1/2 throttle more than
with the 40 slide.
. The needle jet is in the center of the carb and works in
conjunction with the jet needle and main jet. The jet needle slides up and down inside the
needle jet controlling fuel flow coming from the main jet which is screwed into the
bottom of the needle jet. Typically, there is no need to change the needle jet except for
wear.
. As the name implies, the jet needle or needle is a tapered round piece
that fits into the center of the slide and controls fuel coming up through the needle jet and
main jet between 1/4 and 3/4 throttle. The needle is very adjustable buy
moving the clip to one of the 5 notches on the top of the needle or by using a
different needle with a different straight diameter (A), tip diameter (B), or
length of taper (C). There are at least 25 different needles available for the
PHBG 19mm carb used on the Pro Sr. The needles used in this carb are ?W?
needles such as the W7, W9 and W4 to name a few. The needle affects the
greatest range of operation, 1/4 to 3/4 throttle, where most riding/racing
occurs, so don?t forget this vital circuit. Clip positions are counted from the
top (flat side) of the needle down. Moving the clip down raises the needle in the needle
jet and will allow more fuel to pass earlier in the throttle opening process richening the
mixture closer to the 1/4 throttle position. Moving the clip up lowers the needle in the
needle jet and restricts fuel flow leaning the mixture closer to the 1/4 throttle position. By
changing to a different needle with a different shape you can richen or lean the mixture
across the entire effective range (1/4 to 3/4 throttle).
. This is the jet in the center of the carb and screwed into the bottom of
the needle jet (atomizer). The pilot jet and starting (choke) jet will always be off to the
side when looking at the bottom of the carb. The main jet limits the maximum flow of
fuel through the carb and affects from 3/4 to Wide Open Throttle (WOT).
. This jet only operates when the choke is pulled which riches the
mixture for starting a cold engine. When an engine is cold the fuel does not atomize well
and has a tendency to condense into droplets on the cold metal in the intake. The choke
richens the mixture to get needed fuel to the combustion chamber for starting and as the
engine warms it becomes more efficient and requires less fuel in the mixture. This jet is
commonly mistaken for the pilot jet by carb newbies. The choke can be used a diagnostic
tool for jetting as you will see later. Note: Make sure you turn it off before the little racer
leaves the line or they will not be happy with you!
. The float and float needle control the
level of fuel in the float bowl where the jets are located. Fuel from the tank flows in
through the float needle and fills the bowl. The float rises in the fuel and the tab on the
float pushes up on the float needle shutting off the flow of the fuel into the bowl. The
bowl level is changed by bending this tab. If the float level is too high fuel can be forced
up the jets and cause a rich condition. If the level is too low a bog can develop as the
throttle is opened quickly and the bowl is drained below the jets before the bowl can
refill.
. As the name implies, this screw sets the idle level. As the
screw is turned in it ?wedges? under the slide raising it and increases idle RPM. Don?t
confuse the idle screw with the mixture screw. The idle screw can be adjusted without
tools where the mixture screw requires a screw driver to adjust it.
Tuning:
Since the bikes are too small for us tuners to ride and the riders are young and have
limited ability to provide feedback, you?ll have to learn to read spark pugs and listen
closely to the engine as it performs on the track. Before long you will be an expert and
lines of frustrated dads/moms will be forming at your trailer in the pits. You will speak
with great pride when telling the other dads/moms about running the same plug for the
past 6 months and you will smile at them as you role to the line, start the bike, warm it up
and stage while the others strain to lift their kid and bike, rev the engine to the moon
spewing smoke and then slam on the brake stressing the drive train several times and then
pace nervously behind the bike with a pocket full of spare pugs and wrenches hoping the
gate drops before it loads up or fouls the plug.
First things first. Make sure the carb is clean and then clean it again. Install a clean oiled
filter and a fresh batch of fuel. Use the filter, oil, amount of oil, fuel and pre mix oil and
mix ratio you intend to race with while jetting. Make sure the carb clamps and intake
bolts are tight and free from leaks. Warm the bike up to operating temperature before
starting and ensure you have a fresh properly gapped plug installed. Remember this first
full jetting will be based on the temperature, altitude and humidity level of the day and
place you make the settings. You will need to fine tune your jetting based on the
conditions at the track at the time of the race. Jetting is not a set-it-and-forget-it item!
Lets review the 4 main circuits, their components and the ranges they affect before we go
any farther. Remember that all of the circuits overlap each other and changes to one will
affect the others to some degree and may require you to go through the procedure several
times as adjustments are made.
? Circuit #1 ? Mixture screw form idle to 1/8 throttle and pilot jet from 1/8 to 1/4
throttle.
? Circuit #2 ? The slide affect from 1/8 to 1/4 throttle.
? Circuit #3 ? The needle and clip position affects between 1/4 and 3/4 throttle.
? Circuit #4 ? The main jet affects from 3/4 to WOT.
At this point you would typically place some tape on your throttle housing and throttle
grip and mark the throttle at 1/4 , 1/2 , 3/4 and WOT to help diagnose which circuit is
causing the problems while test riding the bike. As stated before, this is not feasible on
50cc machines and we will have to rely on our little test pilots feedback, plug readings
and the sound of the bike to make adjustments. Lets get started. Now that the bike is
warmed up and race ready and your test pilot is in full gear, have him/her ride the bike in
an area where they can achieve WOT for several (10?15) seconds such as a large oval
track, a long flat open field or the longest straight on the local practice track so we can
check the main jet by doing a ?plug chop?. I do this on our 65 down the street in front of
our house in our development. The neighbors love it!! You can start with the factory
jetting or one of the recommendations from Todd, Alex or Ken, but it?s better to start rich
and work towards lean.
Plug chop defined: While riding at WOT the rider quickly and simultaneously closes the
throttle, pushes the kill switch and applies the brake to safely coast to a stop (off the
track). Do not let the bike idle and big bikes must also pull the clutch in.
Main jet tuning: After your rider performs a plug chop, remember don?t
restart the bike, no idling and push it back to the pits, let the bike cool and
remove the plug. What does it look like? You want to be looking mainly at
the ?white? insulation around the center electrode. If it?s still white, like a new one, the
main is too lean and you need a larger main jet right away! If it?s black and dry like soot
you can drop a main jet size, install a new plug and repeat the above procedure. If it?s
light brown, tan or gray you?re good! (see picture to the
right)
: Start the bike on the stand and
warm it up. Set the idle to the minimum RPM that the bike
will stay running at. Turn the mixture screw in and out in ?
turn increments and listen to the idle speed. Find the point
where the idle is max. Now kill the engine and turn the mixture screw in counting the
number of turns until you gently bottom the screw into the carb. Go easy or you can
break the tip off the screw in the carb. Now back the screw out the same number of turns
you counted while screwing it in. If you are less than 1 turn out or more than 4 turns out,
you need to change the pilot jet and repeat this procedure. Ideally, the mixture screw
should be between 1 ? and 3 ? turns out, with the proper pilot jet, to be most effective. If
your mixture screw is a fuel screw : Less than 1 turn out = smaller pilot. More than 4
turns out= larger pilot jet. If your mixture screw is an air screw : Less than 1 turn out =
larger pilot. More than 4 turns out= smaller pilot jet. After you change the pilot, repeat
the mixture screw adjustment procedure.
Start the bike on the stand and warm it up. Twist the throttle quickly from
idle. If it bogs and then revs with a booooooowang sound, the pilot is lean. Install the
next larger pilot and repeat. Be sure the engine is up to temperature, because many bikes
will have this ?lean bog? off idle when they are cold. When then pilot is correct the
engine should idle with out excessive smoke or loading up and it should rev cleanly and
quickly from idle. I like to start rich on the pilot and keep going leaner until I get the lean
bog and go back up a size or two.
Needle and clip tuning: Watch and listen to the performance of the engine when the rider
rolls on the throttle from almost closed to more than 1/2 open as when coming out of a
turn on the track. Listen and watch for rich or lean symptoms in the operating range. You
can also use a plug reading to tune the clip position, but it?s not as easy. Follow the same
procedure as the WOT plug chop, but have your rider try to maintain 1/2 throttle for an
extended period (15-30 seconds) and do the plug chop procedure of closing the throttle
and pushing the kill switch simultaneously. Pull the plug and check it. If it?s rich, raise
the clip and drop the needle. If it?s lean, lower the clip and raise the needle. Retest after
each change. If the engine performs best with the clip in the top position you may want to
try a leaner needle. If the best performance is with the clip on the bottom position
consider a richer needle design. Generally, you will use the second or third clip position
on the KTM 50s.
Generally the factory slide works fine in most situations. If you are having a
bog issue off the start or between 1/8 and 1/4 throttle a richer slide may do the trick. A
slide with a higher number is leaner than a slide with a lower number. The numbers refer
to the size of the half moon cutout on the air filter side of the slide. When putting the
slide back in the carb make sure the pin through the side of the carb is in place that rides
in the grove down the slide. This pin and grove keep the slide from turning in the carb.
Remember to keep things clean and put the top of the carb, where the throttle cable come
in, back on in the proper orientation. It will go on in either direction, but will bind if
backwards. The cable is off to the side of the slide, since the needle is in the middle, so
make sure the carb top lines up the cable.
Symptoms of improper jetting:
Jetting is too rich:
? Rich main jet ? blubbers and will not rev out at WOT.
? Rich pilot or mixture screw setting ? engine won?t idle and idle screw is ineffective.
Loads up at idle and fouls plugs.
? Rich needle/slide ? motor stumbles between 1/8 and 1/2 throttle and then cleans up.
? Plug is dark and either wet or dry and sooty.
? Poor acceleration and excessive smoke.
Jetting is too lean:
? Lean main jet ? sounds like it is running out of gas at WOT , white plug color,
running hot and lacks power.
? Lean pilot or mixture setting ? quick throttle stabs result in a boooooowang sound off
of idle.
? Plug check shows a white plug or very lightly colored.
? Revs quickly, but lacks power.
? Pinging or rattling sound.
You can use the choke to diagnose a rich or lean condition. The choke will richen the
mixture across all circuits. Simply apply the choke half ways on and see if the condition
gets better or worse. If performance improves, the circuit being tested is lean. If
performance gets worse, the circuit being tested is rich.
Remember jetting is a dynamic setting and needs to be changed to meet the conditions
you are riding or racing in. Sure your kids bike might run fine with the factory jetting or
the commonly used settings, but is it ideal to make all the power the engine is capable of?
As with the adjustable clutches, jetting is a maintenance item that requires a lot of
attention to promote maximum performance, so don?t shortcut the process.
Environmental and altitude related mixture adjustments
Condition Mixture will be Required adjustment
Cold air Leaner Richer
Warm air Richer Leaner
Dry air Leaner Richer
Very humid air Richer Leaner
Low altitude Standard None
High altitude Richer Leaner
Low barometric pressure Richer Leaner
High barometric pressure Leaner Richer
ktm 50 carbtuning.pdf
IF IT AINT BROKE, FIX IT TILL IT IS! 
I ride to have fun, and 2T is fun, scary fun sometimes, but fun..............!psm
Source: https://www.dirtbikeworld.net/forum/forum/manufacturers/ktm-forum/95724-ktm-50-mini-sx-s-are-doing-my-head-in
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