# The 1-2-3's/a-b-c's of jets and screws

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I need help to understand the basics behind the rational...

(maybe it's the Dyslexia, i dont know... but i never seem to get the jet thing right when it counts)

The basics as I understand it:

Needle:

to riase the needle (lower the clip) will LEAN THE BIKE.

T or F

Main jet #: the lower the #, the LEANer THE BIKE. T of F

Pilot jet #:

the lower the #, the leaner the bike (but when to do that vs the main)

Air Screw: Turning it INWARDS will LEAN THE BIKE? T or F

a few senerio's:

1) HOTDAY (90degs) @ sea level -vs- HOTDAY @ 5K above sea - BIKE POPS WHEN NOT ON THE GAS

- the bike wants/needs more air @ 5K vs sea level. so to fix that you can either - lower the clip(raise the needle) change the main jet to a smaller number - RIGHT?

2) COLDDAY (50 degs) @ sea level vs COLDDAY @ 5K above sea

THE BIKE BOGS/chokes WHEN TRYING TO GIVE IT GAS

- the bike needs less air richen it by increasing the number on the main or raising the clip(lowering the needle)

3) hotday @ 5K- with no backfire but bike has weak power up hills??? LEAN IT MORE OR ???

Can someone give it to me in a nutshell - something that I can fold up and keep in the liner of my helmet!!!

ANYTHING WILL HELP

Main Jet #'s -

Pilot Jet #s -

Needle clip setting -

Air screw turns -

what happens when you do these things...?

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Main -- larger # equals richer

Pilot -- larger # equals richer

Fuel Screw -- turning OUT equals richer

Needle -- raising needle/dropping clip equals richer

GENERALLY speaking a "cutting out/rough acceleration" sound/sensation implies a rich condition while a "gasping" sensation implies a lean condition. At altitude and/or hotter/more humid conditions you must jet leaner. At lower elevations and/or cold temperatures you must jet richer. GENERALLY speaking.

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Needle:

to riase the needle (lower the clip) will LEAN THE BIKE.

T or F

false,richens the bike.

Main jet #: the lower the #, the LEANer THE BIKE. T of F

true

Pilot jet #:

the lower the #, the leaner the bike (but when to do that vs the main)

true........when to do what?

Air Screw: Turning it INWARDS will LEAN THE BIKE? T or F

its a fuel screw,in is leaner.

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1) HOTDAY (90degs) @ sea level -vs- HOTDAY @ 5K above sea - BIKE POPS WHEN NOT ON THE GAS

- the bike wants/needs more air @ 5K vs sea level. so to fix that you can either - lower the clip(raise the needle) change the main jet to a smaller number - RIGHT?

neither,the throttle is closed so neither is in play.popping can be either rich or lean.but if its worse at lower elevation then its lean.open the fuel screw,but no more than 2.5 turns.if it wants more than 2.5 turns,you need a bigger pilo jet.

a slight pop on decel is normal.

2) COLDDAY (50 degs) @ sea level vs COLDDAY @ 5K above sea

THE BIKE BOGS/chokes WHEN TRYING TO GIVE IT GAS

- the bike needs less air richen it by increasing the number on the main or raising the clip(lowering the needle)

colder makes the jetting leaner.richen the needle.

) hotday @ 5K- with no backfire but bike has weak power up hills??? LEAN IT MORE OR ???

leaner main jet.

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Is the "pilot air screw" and the "fuel screw" the same screw? So in is leaner?

Thanks, Mike -

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no,they are different.

pilot air screw = out is leaner

fuel screw = in is leaner

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Burned, is this picture (from previous post) correct . Is the front screw (closest to engine) the Pilot Air Screw or the Fuel Screw. My manual lists it as Pilot. Would you please clarify where each are for me, on each carb .

Thanks, Mike -

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your manual calls it a pilot screw,not a pilot air screw.its meters fuel,not air.so its a fuel screw.

the one in the pic is the fuel screw.

on a fcr a pilot air screw comes in after market units and is sold as a conversion for the pilot air jet.it is located under the intake bell of the carb.

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Ok, (I think), Its a Fuel screw, forget about PAS on the CV? Forget about PAS on FCR unless aftermarket replacement for Pilot air jet (to make adjustable). Here's a pic from my manual....unless I'm completely screwed up (no punn) it says pilot, but perhaps they mean Pilot "FUEL" Screw and I assumed Pilot "air" Screw because of reading so many posts referring to PAS? Thanks for the help with this.

Mike -

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thats a fuel screw.

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Thanks for setting me straight, I'm learning!

Mike -

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The way I understand the screw issue (that's the screw issue not THE screw issue ) is that in 4 strokes, the screw is located bewteen the carb and the intake on the cylinder. This is a fuel metering screw. So, turning it out causes a richer mixture. With 2 strokes, the screw is located on the air intake side of the carberator. It is an air screw and turning it out allows more air and less fuel (so a leaner mixture).