Adjusting Your Airscrew/Pilot Jet

Awk08

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Jan 30, 2009
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after repeatedly typing this, it's time for a linkable thread :)

all this is assuming your carb is immaculately clean, float height correct, your engine has been leakdown tested and proven airtight, as well as a freshly cleaned or new airfilter, good fresh fuel/oil mixed correctly for that specific oil and a fresh B8ES sparkplug.


this is your airscrew:


keihin 34mm PJ
2cf3wpw.jpg



stock 26mm mikuni:
16hu2au.jpg


on the stock blaster carb.... i've run one on everything from a stock, to a ported and piped 200cc engine, and have never needed anything but the stock 32.5 pilot.
my airscrew setting "said so" !!!! (see below)
I guess it is possible for someone at low/sea level elevation to MAYBE need to jump to the 35 pilot ?? but at my 1800'+, I have not.
again...the airscrew setting will tell you.
If you didn't $pring for a new larger carb for your new 240 cylinder, you may have to jump up too ?? but i highly suggest at least a 32-35/36mm carb for a BBK


too rich or lean airscrew setting/pilot size will effect your whole jetting range,
as will an incorrect float height......
( http://www.blasterforum.com/carburetor-138/float-heights-how-adjust-them-50565/ )
these 2 must be set before moving on to the needle size/clip settings and main jetting.
If you are already plug chopping main jets, before checking/setting your float, airscrew, pilot and needle settings....you're pissing in the wind !
you must start at the bottom and work up, each lower setting effects all jetting ranges above it.

the correct airscrew setting will determine if you need to change your pilot jet.
less turns out = less air into the pilot circut = richening it.
more turns out = more air = leaning it.

IMO...the optimal setting for the airscrew is 1.5 turns out, this allows you adjustment room in both directions for elevation and temperature changes as the temps/elevation change, even daily as needed.
if you end up on the borderline...1/2 turn, or 2.5 turns out, chances are you can go up or down 1 size to acheive around 1.5 turns and have some adjustment.

to adjust the airscrew....start at 1.5 turns out from lightly tight. (lefty loosey/righty tighty)
get the bike warmed up, revving it if needed to keep it running.
turn your idle up slightly to help it stay running and overcome the incorrect settings of the adjustment process.

you are looking for the airscrew setting that acheives the highest idle.

from the 1.5 turns out, slowly start turning the screw in 1/2 turns at a time, allowing 15-20 seconds between turns for the engine to "catch up" to each new fuel/air setting.
repeat in the other direction from 1.5 turns out to 2.5-3+ turns out
find the turns in or out that the engine idles the highest, double check it, kill the engine and turn the screw in completely counting the turns as you do, write it down and return it to the newly found high idle setting.
if this # of turns is between 1/2 and 2-1/2 turns out, you are golden.

now you can do 1/8th turns each direction until it revs cleanly past 1/2 throttle, this can also be done while riding it to acheive good throttle response or daily to accomodate changing conditions

If the highest idle setting is below 1/2 turn out, you need a richer/larger pilot jet.
If highest idle setting is above 2-1/2 turns out, you need a smaller/leaner pilot jet.
If the airscrew settings have no effect on the idle you need to jump a couple sizes either direction until you find one that the airscrew setting will have an effect on using the known jet sizes for various carbs as a guide

I'm not positive about the larger mikuni's ?
most of the larger keihins can be safely jetted starting around a 50 pilot and using the airscrew setting to determine if you need to go up or down.
I have run a 45, and currently a 48 in my 34mm pj with my mods

here's some other known jetting info to get you started.........
http://www.blasterforum.com/engine-13/what-jets-you-using-28981/
 
Awesome post man. SCD just pointed me to it. Getting ready to set my Kehien again after adjusting my floats.
 
I got2001 blaster hasn't started because every time ikick it it back fires there's no Thor system and there's no ideal screw or a hole going all the way threw the card do I need to out a hole threw? So it will start? Need help
 
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you need to add an idle screw when deleting the TORS unit that sits on top of the stock carb.
did you delete that and add a regular carb cap ? or just delete the epectrical part of the TORS ?

if the unit is still on top of the carb, the idle screw is the big nickel sized screw on top, accessed from under the seat, lift rubber flap and look under fuel tank.

if you have a regular carb cap (?) you need to add an idle screw.......
http://www.ebay.com/itm/Yamaha-Blas...m483f9bab46:m:mCy6qSy6-B2iRE5hnct94tw&vxp=mtr

although the idle screw has nothing to do with this airscrew thread, they are 2 different things.



also, backfiring is usally 1 of 2 things, bad/broken reeds or sheared flywheel keyway that has allowed to flywheel to rotate out of time = sparking at the incorrect time during the piston cycle
 
after repeatedly typing this, it's time for a linkable thread :)

all this is assuming your carb is immaculately clean, float height correct, your engine has been leakdown tested and proven airtight, as well as a freshly cleaned or new airfilter, good fresh fuel/oil mixed correctly for that specific oil and a fresh B8ES sparkplug.


this is your airscrew:


keihin 34mm PJ
2cf3wpw.jpg



stock 26mm mikuni:
16hu2au.jpg


on the stock blaster carb.... i've run one on everything from a stock, to a ported and piped 200cc engine, and have never needed anything but the stock 32.5 pilot.
my airscrew setting "said so" !!!! (see below)
I guess it is possible for someone at low/sea level elevation to MAYBE need to jump to the 35 pilot ?? but at my 1800'+, I have not.
again...the airscrew setting will tell you.
If you didn't $pring for a new larger carb for your new 240 cylinder, you may have to jump up too ?? but i highly suggest at least a 32-35/36mm carb for a BBK


too rich or lean airscrew setting/pilot size will effect your whole jetting range,
as will an incorrect float height......
( http://www.blasterforum.com/carburetor-138/float-heights-how-adjust-them-50565/ )
these 2 must be set before moving on to the needle size/clip settings and main jetting.
If you are already plug chopping main jets, before checking/setting your float, airscrew, pilot and needle settings....you're pissing in the wind !
you must start at the bottom and work up, each lower setting effects all jetting ranges above it.

the correct airscrew setting will determine if you need to change your pilot jet.
less turns out = less air into the pilot circut = richening it.
more turns out = more air = leaning it.

IMO...the optimal setting for the airscrew is 1.5 turns out, this allows you adjustment room in both directions for elevation and temperature changes as the temps/elevation change, even daily as needed.
if you end up on the borderline...1/2 turn, or 2.5 turns out, chances are you can go up or down 1 size to acheive around 1.5 turns and have some adjustment.

to adjust the airscrew....start at 1.5 turns out from lightly tight. (lefty loosey/righty tighty)
get the bike warmed up, revving it if needed to keep it running.
turn your idle up slightly to help it stay running and overcome the incorrect settings of the adjustment process.

you are looking for the airscrew setting that acheives the highest idle.

from the 1.5 turns out, slowly start turning the screw in 1/2 turns at a time, allowing 15-20 seconds between turns for the engine to "catch up" to each new fuel/air setting.
repeat in the other direction from 1.5 turns out to 2.5-3+ turns out
find the turns in or out that the engine idles the highest, double check it, kill the engine and turn the screw in completely counting the turns as you do, write it down and return it to the newly found high idle setting.
if this # of turns is between 1/2 and 2-1/2 turns out, you are golden.

now you can do 1/8th turns each direction until it revs cleanly past 1/2 throttle, this can also be done while riding it to acheive good throttle response or daily to accomodate changing conditions

If the highest idle setting is below 1/2 turn out, you need a richer/larger pilot jet.
If highest idle setting is above 2-1/2 turns out, you need a smaller/leaner pilot jet.
If the airscrew settings have no effect on the idle you need to jump a couple sizes either direction until you find one that the airscrew setting will have an effect on using the known jet sizes for various carbs as a guide

I'm not positive about the larger mikuni's ?
most of the larger keihins can be safely jetted starting around a 50 pilot and using the airscrew setting to determine if you need to go up or down.
I have run a 45, and currently a 48 in my 34mm pj with my mods

here's some other known jetting info to get you started.........
http://www.blasterforum.com/engine-13/what-jets-you-using-28981/
Any linkable threads for cleaning a carb thoroughly?
 
you need to add an idle screw when deleting the TORS unit that sits on top of the stock carb.
did you delete that and add a regular carb cap ? or just delete the epectrical part of the TORS ? I have a blaster with tors electrical removed but it still has cap on carb with nickel size screw.how do u adjust that..it was turned all the way counterclockwise when i bought quad

if the unit is still on top of the carb, the idle screw is the big nickel sized screw on top, accessed from under the seat, lift rubber flap and look under fuel tank.

if you have a regular carb cap (?) you need to add an idle screw.......
http://www.ebay.com/itm/Yamaha-Blas...m483f9bab46:m:mCy6qSy6-B2iRE5hnct94tw&vxp=mtr

although the idle screw has nothing to do with this airscrew thread, they are 2 different things.



also, backfiring is usally 1 of 2 things, bad/broken reeds or sheared flywheel keyway that has allowed to flywheel to rotate out of time = sparking at the incorrect time during the piston cycle
 

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