The Best Two Stroke Jetting Video You’ll Ever See!


alright guys I’m gonna be covering the
art of jet eot stroke today now this is gonna be a long super detailed video so
you may want to sit down crack your cold one and enjoy this video
alright let’s get started so let’s start at the simplest of levels
what exactly is Jenny so jetting is changing out these little cylinder
shaped pieces that have a whole throat just a tiny microscopic hole inside the
carburetor here to allow for more or less fuel to enter the engine when you
install a smaller jet that lets less fuel into the engine causing a leaner
mixture and on the other side a bigger jet creates a richer mixture so that’s
like the bare basics of jetting and so what we’re trying to achieve here is the
optimal air to fuel ratio and for most engines that’s gonna be 14 point 6 to 1
so that’s one gram of fuel and fourteen point six grams of air to combine to
make the perfect ratio now that number doesn’t really matter and we’re not
going to use it for jetting and all more for just information purposes so what
happens when an engine isn’t jetted correctly if it’s too rich mean too much
fuel it’ll bog out like you whack the throttle and it’ll cop out and then it
won’t rub out all the way and then it’ll cough and sputter throughout the upper
rpm range too and if it’s too lean it’ll have a hanging idle meaning you rev it
up and it takes forever to idle back down lacks power you may hear like a
knocking noise to it it feels like super zingy it’s kind of hard to describe that
term and then it’ll run super hot too if it’s really lean and that’s what leads
to an engine seizure so obviously both of these are kind of dangerous
conditions of being especially being lean that’s what will destroy your
top-end your crank and then if you’re too rich you could cough out or bog out
when you’re riding especially kind of face of a jump or you know whoop section
or whatever it might be and that obviously would not be a good thing to
happen alright now that you kind of understand what jetting is all about
let’s talk about a few things before we actually start getting so say your bikes
run like ass and you want to dive just right in the jetting and figure this
thing out but there’s a couple simple things you need to check
/ before you actually start pulling the carburetor apart and switching out Jets
so first thing popping a new spark plug make sure your filter is clean those two
things will make a big difference when it comes to jetting you have a plugged
air filter that will just throw everything for a loop
you know same thing with a a worn or really valid out spark plug make sure
you have good compression may want to test the compression before you actually
start jetting to diagnose any issues with that and then obviously make sure
you have a clean carburetor there’s no plug jets or plugged up vent hoses
that’ll really mess things up too if you just rebuilt your bike make sure you
break it in that actually changes quite a bit once you have it broken in they’ll
create more compression and change how much fuel the engine requires oh and
another big thing is float height if you don’t have the correct flow height
that’ll actually change how much fuel is available in that float Bowl for the
Jets that stuck out of so if that’s off that’ll make the whole jetting process
kind of a nightmare and one more thing you want to make sure
your bike is warmed up completely before you go out and test it just even swear
I’m properly a cold bike runs way different than a warm bike does alright
enough talking I’m gonna pull the carburetor off of this bike take it
apart completely show you the ins and outs of the carburetor all the circuits
what effects how it runs down low the mid-range and then when you’ve got it
pegged up top so just kind of cover all the basics before we actually start with
the jetting process oh and one more thing most bikes you can get to the
carburetor or jet the carburetor if it’s still on the bike you can do it with
this one you just got twist the carburetor in
there but for this time I’m just gonna pull it completely off show you guys the
ins and outs like I was talking about earlier and then we can start swapping
out jets and all that I’m gonna see how fast I can pull the carburetor off of
this bike I’m hoping I can do it in under two minutes start the timer right
now so there’s four components here to the
carburetor that we’re going to check out that effective jetting and how the bike
runs at a certain rpm the first thing we’re gonna look at is the air screw on
the backside of the carburetor don’t mistake it for the idle screw which is
usually on a throttle slide and towards the center of the carburetor and then
number two we’ve got the needle on the throttle slide and then inside the float
Bowl we’ve got the main jet in the pilot jet so the football is what contains the
fuel and that’s what the Jets draw feel from and ultimately what provides fuel
to the engine all right I’m gonna pull the float Bowl off and show you guys the
main jet the pilot jet and the floats as well so here we’ve got the main jet the pilot
jet down here and the floats and then hanging on this little tab here on the
floats is the float needle and that’s what controls the fuel flow into the
float Bowl earlier in the video I was talking about float height and how
important it is to have the correct float height so the float height
ultimately determines how much fuel is available in the float Bowl for the Jets
to access and if you don’t have enough fuel in there the bikes gonna be
starving for a few obviously and if there’s too much fuel in the float Bowl
the bikes to me bogging out stumbling and just not running too well so to
check your float height we’re gonna let the floats extend all the way and then
tilt the carburetor back and let them settle so right there they’re settled
but they’re not pushing in the float valve so right there would be pushing in
the float valve you want it sitting just right up on top and then you measure
from the top of the float here to the float Bowl gasket surface and every bike
is gonna be different so check your manual to see what the correct
specification is and to adjust the float height you just bend this little tab
that the float valve is hanging from so when you bend it down that increases the
float height and bending it up goes the opposite way so definitely before you do
any jetting make sure you have the correct float height in your carburetor
there’s a number of components here that affects how the bike runs throughout the
RPM range so we’re going to start at the very bottom so from idle to quarter
throttle is the pilot jet this one right here and the air screw so the air screw
is what controls how much air is being delivered to the pilot jet and this
screw is how you tune in the pilot jet as well so with the air screw the
farther you go in the less air is going to the pilot jet which creates a richer
mixture and then turning that screw out brings more air in and creates a leaner
mixture I’m going to talk about the air screw and the pilot jet later on in the
video but basically how you tune in the pilot jet with the air screw is when
you’re at a certain amount of turns out with the screw that’ll determine whether
you should go up or down on the size of the pilot jet and then next up what
controls from quarter throttle to 3/4 throttle is the needle here on the
throttle slide so you can adjust it up or down
and that changes how much fuel is being delivered throughout that throttle range
and there’s actually two more pieces here that factor in the jetting as well
but they’re not that applicable to most situations so I’m not really going to
touch on it a whole lot so you can swap out your throttle slide for something
different with a different cutaway or a different shape and that’ll affect how
much air is being let into the engine which obviously affects jetting and you
can swap out your needle for something different to one last longer or shorter
or a different taper here on the end but you’re gonna notice the biggest
difference in adjusting your existing needle up or down so the throttle slide
just slides right into the carburetor right here and when you twist the
throttle the slide goes up and down and allows the air and feel mixture into the
engine so that needle goes down into the float Bowl and through the main jet so
when you twist the throttle that needle allows fuel from the main jet to enter
the engine and move the needle up or down you just reposition the clip on the
needle in a different position there’s usually like five or six different slots
on the needle so when you move that clip down that raises the needle and creates
a richer mixture and then when you raise that clip that lowers the needle and
creates a leaner mixture and then last up we’ve got the main jet this jet makes
the biggest difference of all your jetting changes and it’s gonna be the
most common jet you’ve got to swap out so this one controls from half throttle
to wide-open throttle to recap we’ve got the air screw and this is what you use
the tune in the pilot jet so the pilot jet and the air screw control from idle
to quarter throttle and then we’ve got the needle which controls from quarter
throttle to 3/4 throttle and last up is the main jet and this affects from half
throttle to wide-open throttle so I’m gonna get this carburetor back together
put it on the bike and then we can start the tuning process one last thing to discuss before we dive
into jetting and that is what affects jetting and what kind of things require
you to reject and that would be weather so like humidity temperature and then
elevation is a big one too modification so if you did like intake or exhaust
modifications of your bike that would require you to read jet and then
maintenance things too like if you’re lowering compression where you got a
dirty air filter or other things just aren’t up to par that will affect
jetting too and how temperature affects your jetting is when the air is warmer
it’s less dense and so you’ll need to go down on your jet to compensate so less
air available means the requirement for less fuel and that when you go up in
elevation the air is thinner so same concepts temperature less air available
requires you to go down on your jet so for modifications generally that
requires you to go bigger on your jet so if you have a more free-flowing intake
or exhaust that is more air traveling through and that requires you would have
more fuel as well one thing that’s super important with jetting and will save you
a lot of frustration is just going step by step and only make it one change at a
time say if you change our needle position and your main jet to the same
time and it negatively impacts how your bike runs you’re not going to know which
one affected that so just keep it simple so the first thing we’re gonna tune in
here is the air screw and the pilot jet now the pilot jet is gonna be the one
adjustment you’re gonna touch the least once you set it you’re pretty much good
to go with that and for the air screw when you change elevation or the
temperature or humidity changes that is gonna be a screw you’re going to adjust
so how do you know if you have to lean or to rich of a pilot if it’s to lean
the idle will surge meaning you’ll go up and down up and down and then when you
crack throw all really quickly it’ll cut out or bog and then it’ll have trouble I
linked down as well so you rev it up and it takes forever to idle back down and
then when you have a rich pilot jet it’ll sputter when you open the throttle
it’ll follow up plugs and it’ll be really hard to start as well so how I’m
gonna tune in the air screw and the pilot jet is by going three turns out on
the air screw and then work my way back in half a turn at a time until the
engine starts to stumble and the idle isn’t very smooth then I’m gonna go back
out half a turn at a time until that idle smooths out and the throttle
response is crisp and wherever I end up with the air screw as far as turns out
that will determine whether I need to go down or up on the pilot jet and there’s
a few other methods out there for tuning in the air screw such as adjusting the
screw until the engine reaches its highest rpm but I’ve always found that
going by the sound of the bike the throttle response and the idle that’s
always worked best for me now I’m going to fire up the bike let it warm up and
then turn out this air screw the three turns out and then work my way in from
there one one half to two and a half and three
so the bike died when I turned that screw all the way in but now I’m at
three turns out I’m just gonna start it back up and play with that screw some
more so you could hear right there the thaw
response is pretty crisp but I’m gonna start turning in the screw until it
starts to bog out or starts to stumble when I turn the throttle and so as
you’re turning in that air screw and you get to a really rich position it’ll
sound like the choke is on so we’ll have like a sputtering or like a really
choked up sound to it and as you heard right there it bogs out
pretty good and the idle just goes down really quick so definitely too rich of a
position so I’m just gonna work my way out a half a turn out of time until it
cleans up and then I’ll count how many turns out I am on that screw so right there seem to be the sweet spot
I turned the screw out until if our response cleaned up and the Idol
smoothed out as well and now I’m going to show you guys what a lean condition
will sound like I’m just gonna continue turning that screw out and we’ll see
what happens and so right there I’m about three and a
half turns out and as you heard it takes a while for the Idol to go back down to
normal and the throttle response is like super zingy just has like a light
feeling to it the best way I could describe zingy is it just has like a
different sound of the like the ding-ding-ding to it and once you play
around jetting enough and messing with the air screw you’ll be able to identify
the difference between a normal tone of Idol and a lean tone of Idol and
actually I forgot to check how many turns out I was earlier when I got it
running crisp so I’m gonna take you through what it should sound like again
I’m gonna start with the screw all the way in this time and back it out until I
get it run really good again so right there is a sweet spot again
good throw response and the Idol is pretty smooth see how many turns out I
ended up at so that is gonna be a half one one and a half two and so two and a
quarter so I’m gonna set it back to two and a quarter a quarter one right there
so that’s two and a quarter ideally you should have your airscrew between one
and two and a half turns out if you reach the best running condition under
turnout that indicates that your pilot jet is too lean so you have your screws
so far in that you’re barely letting any air in to make that good ratio and then
on the other side of things if you have the screw more than two and a half turns
out to get the best running condition that means your pilot jet is too rich so
you’re letting a ton of air in to make that good ratio once again so to recap
if you’re less than one turn in maybe bump your pilot up one size and then if
you’re more than two and a half turns out bump your pilot down a size so the
only times you really need to mess with the air screw is if you have a really
warm or really cold day where you go up or down in elevation or
you add a modification to your bike so say if there’s a really warm day you
want to lean out the bike a little bit so maybe go a turn out or half a turn
out I should say see how it runs and then if you go up in elevation you’ll
need to lean it out there too so once again try going half a turn out see how
it responds and go from there and then if you add a modification such as a
silencer or a pipe you want to rich ended up most of the time I mean usually
the manufacturer the piper silencer will they’ll tell you what you need to do
there but you may want to go you know half a Turner or turn in and see how the
bike runs with that so say you adjusted your air screw and
you came to the conclusion that you’re gonna need to swap out a pilot jet I’ll
show you how you can go about that without removing the carburetor from the
bike so first you’re gonna have to turn the fuel off and then loosen up the
clamps on both sides the carburetor now with the clamps loose you can pivot it
that way you can get access to the nut on the bottom of the flow bowl here and
on this bike it’s a little easier to remove the front sprocket cover just
gives us a little more access to that football nut so this is a 17 millimeter
and as soon as I loosen this nut up there is gonna be some fuel that’s gonna
come out so have something on hand to catch it or like a rag to soak it up so
to give you guys a little better perspective on how to get access to that
pilot jet we’re gonna lay the bike on its side the jet you see right here is
the main jet super easy to get access to but the pilot is up here in the front
tucked way up in there and you have to fish around with a small flat blade
screwdriver to get to it so you want to push up on the carburetor to get as
straight of a shot with the screwdriver as possible you neither tilt the bike back up and
the pilot jet will fall out or use a set of tweezers or needlenose pliers to get
that pilot jet out of there and to get the pilot jet back in there just feed it
in with a set of pliers or tweezers kind of push it up with a screwdriver right
into the hole there you want to get a straight shot with that screwdriver that
way you’re not cross threading those threads either and it’s pretty easy to
get a false tighten here on the pilot jet if you have the screwdriver cocked
at an angle when you’re tightening it it’ll feel like the pilot jets tight but
it actually isn’t and then you go to ride it and it falls out that’s actually
happened to me before and it feels like the world’s crashing
down like the bike just bogs out terribly and you wonder what the heck is
going on you can just put the football cap back on tighten it up give it the
carburetor back into place definitely want to make sure you tighten up your
air boots clamps as well and then you can go test out that jet see how it
responds all right so I’ve got the pilot jet and the Earth’s crew all tuned in
and next up for tuning is the kneel position here in the throttle so
remember this is the part that controls from quarter to 3/4 throttle so to get
to that needle I’ll have to pull the cap here off the carburetor and so if you
have a carburetor that has a screw on cap you know does a twist on cap it’s
pretty easy to get to it with the carburetor still on the bike but with
this carburetor there’s three screws holding the cap on and I’ve always found
it easiest to just pull the whole subframe off like I had earlier on this
bike it’s also easier to remove the top shock bolt that way can pivot Chuck out
of the way and get access to the carburetor it’s only one extra bolt and
it makes life a lot easier you just got to lift up on the back
wheel kind of get some free play there and then just slide out the bolt and the
shock will slide out of the frame slide the carburetor out of the intake
manifold my way can get to these throttle cap screws here and then once
all those screws are out the throttle slide this comes out of the carburetor you got to be really careful with that
needle not to bend it too so this is the needle I’m talking about adjusting and
with this carburetor just pull the spring the tension off the spring pinch
the cable with your fingers like that push it down inside the throttle slide
and it pops out and now we need to get access to the clips here on the needle
so to get the needle out of the slide there’s a bolt that holds the needle
into place so right now I’ve got the clip in the
middle position on the needle and the bike seems be running super good with it
in that spot but I’m gonna show you guys what it would sound like or how it would
run with this needle rich and all the way up so I’ll remove the clip to the
bottom position here so that’s gonna raise the needle and rich in the
condition and so I’m going to put the bike back together and see how it runs so that is the very bottom position here
on the needle and if our days that clip to the top position that would drop the
needle within the slide and lean out the condition so just like when I pulled it apart
gonna have to compress the spring grab the cable kind of pinch it with my
fingers I’ve got a good amount of cable poking out there and I’m just gonna
slide it into the throttle slide and you’ll be able to feel it hook and then
you can release it sometimes this is a bit tricky to do when the cable is still
on the bike so I’ve got the cable hooked inside the slide it’s gonna release the
spring make sure the cable is actually hooked to the slide and then this goes
right back in the carburetor if you guys are enjoying the videos and
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finding the correct needle position can be pretty tricky and it’s a lot easier
to identify a rich condition rather than a lean condition so what I would do like
I did here is start in a really rich condition and work your way leaner until
it clears up so a rich conditions gonna sound like the choke is on it’ll be
sputtering and it won’t accelerate as quickly as it should and so how you test
the needle position is by warm up the bike and going through the gears only
accelerate until about half throttle and if it starts to sputter out or cut out
that means the condition is too rich and you’re gonna have to bump that clip up a
notch so try to just go one notch at a time or like with the Jets just go one
size at a time so I’m gonna take this thing out and see how it runs with that
clip in the richest position so like I was saying it’s gonna bring the bike up
to about half throw all throughout the gears and see if it sputters out or cops
out at all any signs of a rich condition give that another shot here you can hear right in the mid-range
there it’s kind of cutting out which is right where that needle would be
affecting it I’m just gonna make one more run down here and see if I can hear
it a little more a little more clearly right there I’ll go back in the first
gear Yeah right there at super-rich and
that’s where the deal will be affecting in the right in the mid-range so I’m
going to pull this thing back apart and move that clip position now I’m going to
put that clip back into the middle position since it ran really good within
that spot before so I’m gonna let the agent warm up and
then I’m gonna take it down to drive it once again let me go until about a half
throttle and I’ll show you the difference between a needle position
that’s way too rich and one that’s just right so like you heard before about
half throttle it was super sputtering and it just did run very smooth and all
that should be cleaned up now sounds a little better I think it needs
to be cleared out just a little bit more definitely a lot of smoother running yeah that is a lot better keep in mind a keystroke has never gotta
run perfectly food just together so she like what 25 like this isn’t really
meant to be run in the mid-range you know all day you’re supposed to be more
wide open with it so it’s never gonna run just super smooth like a four-stroke
does so you guys heard how the engine runs with that needle in the richest
position but if it’s on the leaner side of things the engine will sound kind of
quiet and have like a dead feeling to it and when you give it full throttle
they’ll hesitate to so you always want to be on the richer side of things with
the needle since it’s kind of hard to identify it whether you’re rich or lean
with that without adjustment there so like I explained earlier you want to
start with the needle and a richer position and then work your way leaner
until it cleans up like I did here and now for the main jet I’m gonna do
something pretty similar to what I did with the needle adjustment gonna start
out really rich to the point where it’s sputtering or it feels like the choke is
on at high rpm and I’m gonna lean it out until all that clears up so once again
you always want to be on the richer side of things just to be safe so right now
the bike runs really good with the main jet where it’s at but I’m gonna bump it
up a few sizes and show you how it run in a really rich condition and then go
through how it tuned in the main jet from there just like any other jetting
change you want to make sure you’ve got the bike warmed up before you go and
test it out so for the main jet it affects from half to full throttle so
I’m just gonna go wide open and see how that fat our main jet affects it
I’m guessing it’s gonna sputter at full rpm because that jet was a size R –
bigger than what I had there previously still need to be cleared out a little
bit there’s a little bit of clutter there though yeah you can definitely hear a little
bit of spider at the very top there where it’s like cuts out it’s not
completely smooth we’re it’s not clearing out 100% of the way so 1/8 overly rich it seems like but
definitely on the richer side of things I’m gonna pop in the old debt I believe
it was the 410 and I’ll show you the difference that makes at the full full
throttle there after running the bike for just a couple minutes with that
bigger main jet we’ve got quite a bit of spooge coming out the silencer here
definitely a bit rich so swapping out the main jet is going to be very similar
to the pilot jet got the bike leaned over on a stand just going to loosen up
the carburetor tilt it off to the side remove that nut on the bottom of the
float Bowl here and then I’ll be able to get access to the main jet alright one last little cashier should
be running pretty crisp now sounds pretty good still a little bit of
sputter up on top but it sounds better than it did before give it another
couple runs down the driveway better sounds really really clean now yeah it’s perfect
just where I wanted to see it at yeah it sounds good yeah I’m gonna call that good right
there if I really wanted to see exactly where
I’m at for for jetting yeah rich I am I could do a chop test in the spark plug
and that would tell me everything I need to know so if you want to see how a chop
test is done on a spark plug just find the jetting or the spark plug
video over on my channel to recap with a main jet you want to start out really
rich and then work your way leaner until it cleans out on top and then just leave
it up right there and it’s always a great idea to do a spark plug chop test
to see exactly where you’re at with that main jet so that pretty much wraps up
the ins and outs of jetting a two-stroke carburetor as you can tell if there’s a
lot of going by the sound and feel the bike and as you do it more and more
you’ll get a really good gauge whether you’re too rich to lean or just perfect
with your setting so it takes a lot of patience at first and you only want to
make one change at a time so if you’re messing with your pilot jet don’t make a
main jet change or a needle position change at the same time and don’t make
your changes too drastic either try to just keep it one size or like a quarter
or half a turn that time and you’ll really be able to dial it in another
good resource for jetting specs is gonna be Google or like a pipe or carburetor
manufacture safety put an F F pipe and silencer on your bike go check out their
website or like pro-circuit or build wherever it might be they’re gonna have
some recommended jegging specs on the website for you to start with and then
you can just kind of find – from there and if you did more extensive mods like
say carburetor a big board or a stroker crank do a google search and forums like
vital MX thumper talk or a few others will pop up and they’ll have a good
baseline spec for you to start with and then you can just kind of work from
there – so the only difference between getting a two stroke and a four stroke
is the air or the fuel screw on a two stroke it’s called an air screw because
it controls how much air is being let into the pilot jet circuit and then on
the four-stroke it controls how much fuel is being let into the pilot jet
circuit as well so on a two-stroke when you turn that screw in it lets
air into the circuit creating a richer mixture and then on a four-stroke it’s
the opposite so you turn that screw in and it lets less fuel into the circuit
creating a leaner mixture one thing I would recommend doing is check in the
color your spark plug throughout the jetting process and afterwards as well
so I have a couple fresh plugs on hand pop them in and keep an eye on them
throughout so I actually did a video a really detailed video on how to check
the color your plugs and there’s also a lot more you can read from a spark plug
as well and you can watch that video by clicking a circle right up here in the
corner now if you think Jegs a bunch of BS and you want a way around it
these electronic carbs are a really good way to go so basically how they work is
they’ve got a metering rod inside of it which is able to automatically determine
how much fuel the engine needs based on airflow volume and temperature so pretty
much eliminates any need for jetting changes so this is the car blow up using
on my cr250 build and I’ll have a ton of videos coming out on the ins and outs of
it how to set it up how it runs and my overall impression of it so lots of
exciting content coming up soon now before I go I need to pick the winners
of the works connection sticker packs from the last video so let’s head over
to the random color picker page and find out who the winners are so this is what
I’m going to use to pick the winners here it is a random comment generator so
I’ve got the URL punched in I’m gonna load up all the comments here should be
quite a few in there probably over a thousand I’m guessing oh yeah
12:27 come down here hit the start button and that’s gonna pick a just
random comment from that video so the only requirement was you had a comment
WC so first winner is motoboys he commented WC pick another one yeah
didn’t say WC you are wrong reference your service manual for the proper spark
plugs readings sorry buddy gonna pick another winner all right
Stephen Holsinger says WC so that’s winner number two and then
Aidan Zollner says would love to see a jetting video doing that right now
WC so that’s winner number three got two more so keep in mind if you see your
name pop up here you got to send me a message here on youtube with your
mailing address all right little dude isn’t winner number four and the last
one is JW films so all of you guys who won the stickers send me a message here
on youtube you just got to go over to the about page on my channel hit the Sun
mess send message button and shoot me your mailing address and I get those
thicker packs mailed out all right that is gonna wrap up the video really hope
you guys enjoyed it and learned a thing or two this video took a ton of time and
effort to create it so I’d really appreciate it if you go hit that like
button and subscribe to the channel as well thanks for watching and keep it
Prime you

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