Finally.... Jetting 101

it's been a while coming but i wanted to sit down and take the time to really get into it.

most of the time I deal in short quick answers to diagnose and repair your engines, Jetting requires a little more time and explanation so that you don't damage your engine.

lets start with elevation,  
higher altitude means less air density which means smaller jets

usually you would need to go down one main jet size for every 1700 to 2000 feet of elevation you ascend.

The example would be, say you are at sea level and you are running a 160 main jet, you'd need a 140 jet for 4000 feet.

in colder conditions you need a larger jet as cold air is more dense so the air temperature plays a role in it as well.


you'll also lose horsepower the higher you go up in elevation.
usually this means You can figure on losing about 3 percent of your power for every 1000 feet you go up.
even with rejetting your ride.


Pilot jet:
pilot jets control the low speed and idle of your mix.
if adjusting the mixture screw won't improve the low-end running speed it's usually time to get a different pilot jet.


Needle:
the needle controls the fuel mixture throughout the midrange. The shape or taper of the needle determines how much fuel goes into the engine at a given throttle position,

usually your needle is for fine tuning once you have the right main and pilot jets figured out.

If the machine stutters or hesitates before it brings on the power, that part of the needle's taper is usually too small and sometimes the only way to fix it is to get a needle with a different taper.
Finding the right needle can be a real pain so try moving the clip first, in minor cases this will fix the problem, but with engines that have been severely bored and have a higher performance exhaust, you are most likely going to need a new needle and a new pilot and main jet.

Main jet:
main jet comes into play at three-quarters open to full throttle
we all know a bigger jet means more fuel to the engine!!!

but it also can mean a cooler running engine,
while a one size smaller jet can mean more power for a while, it can also mean burning your engine out.
a slightly richer main jet can help your engine last longer by helping it run cooler and still make good power, so be sure that your main jet is big enough.

Afterall you can't ride your machine if the rings are shot or the piston skirt is broken due to overheating.

A quick tip is Don't change more than one jet at a time.  
Keep it RUBBER SIDE DOWN!!

JETTING PART 2

OK!!! LETS GET INTO QUICK JETTING YOUR ENGINE!!!

So you bought a jet kit for your machine.
the pilot jet is smaller than the one in your atv, leave the larger stock pilot jet in, and put the largest main jet in your carb.

and install the needle they supplied in the kit.


VERY IMPORTANT!!!!! USING A SHARPIE MARK A STRAIGHT LINE ACROSS YOUR FUEL/AIR MIXTURE SCREW AND ON THE CARBURETOR.
this will give a starting reference  for any adjustments you make to the air/fuel mixture screw, AND BE SURE TO KEEP UP WITH HOW MANY TURNS AND IN WHICH DIRECTION AWAY FROM THE MARK YOU TURNED ON THE FUEL/AIR MIXTURE SCREW!!!! this will allow you to get it back to where it was originally without getting lost or forgetting how many turns or which direction you went.

start the engine and check your idle.
if it wont idle and you cannot get it to idle by adjusting the fuel/air mixture screw and the idle screw, then put the pilot jet in that they sent in the kit.

If you turned the fuel/air mixture screw then turn the fuel/air mixture screw back to where it was before you started.
(hopefully if you turned the screw you kept up with how many turns and which direction)

if your engine starts to rev out of control with the pilot from the jet kit, shut it off as this is a sign that either the fuel/air mixture is too lean or the pilot jet is too small and is causing the egnine to run far too lean.  
letting it run in this condition can cause self detonation on the piston and cause damage if left running. so turn the engine off and adjust the fuel/air mixture screw in 1/2 turn increments.
try turning the fuel/air mixture screw counterclockwise to add more fuel to the mixture.

it if doesn't idle or idles too low try to adjust the air/fuel mixture screw to compensate.

once you have a good idle move on to the Main jet.
ride your atv at full throttle for a minute and kill the engine.
be sure not to burp the throttle or rev it up just to hear the engine
(i know this is hard to keep from doing but if you rev the engine afterward you change the color of the electrode and wont get a good reading on your main jet fuel mixture.)

ok after running the engine at full throttle and killing it, remove the spark plug and check the electrodes color.
white or gray is too lean, brown or black is too rich.
ideally you want a creamy tan,  about the color of coffee with cream.

black or brown go to one size smaller jet, again ride your atv at full throttle kill the engine and check the spark plug color, still brown or black go one size smaller,

if it's white or gray go back to the larger jet (one size up and adjust the fuel/air mixture.

repeat the ride at full throttle and check your spark plug until you have a creamy tan color.

PLEASE!!! keep up with how many turns you make and which direction you turn it.  this is critical to resetting it to start over if necessary.


Finally, time to fine tune!!! (if necessary) if you have the creamy tan color but the engine hesistates or stutters when you give it throttle, change the the needle groove, try putting the clip on the needle on a groove closer to the top of the needle first, (higher on the needle)

if no change then go higher.

you should have that engine screaming before long!!!


Disclaimer:

because we do not know the mechanical ability of those using this guide we accept no responsibilty if your engine is damaged or you or someone else are personally injured by following these steps.
if you are unsure that you can do this yourself please take it to a qualified professional to have it rejetted. Both, Wolf Performance and Atv Rider do not want you to get hurt or damage your atv.  this is a "use at your own risk" guide to jetting.  
Keep it RUBBER SIDE DOWN!!

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Keep it RUBBER SIDE DOWN!!

back to the top for those who need it  
Keep it RUBBER SIDE DOWN!!

back to the top  
Keep it RUBBER SIDE DOWN!!

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Keep it RUBBER SIDE DOWN!!

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Keep it RUBBER SIDE DOWN!!

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Keep it RUBBER SIDE DOWN!!

All I can say is thanks for this!  I've been working on trying to get my blaster tuned in for a few years now and today was the magic day!  Thanks a ton!  

I agree Wolf1 is the man.  
Heres my toys
YFZ450 "06" jet kit, zip tie mod, cam mod, sold
Raptor 350 "06" stock, sold
Predator 90 "06" stock, sold

bump  
Keep it RUBBER SIDE DOWN!!

bump  
Keep it RUBBER SIDE DOWN!!

ttt  

carb problems follow this.  
Heres my toys
YFZ450 "06" jet kit, zip tie mod, cam mod, sold
Raptor 350 "06" stock, sold
Predator 90 "06" stock, sold

yeah it keeps going to the bottom, wish we could sticky this somewhere on here so it wouldn't be so hard to find......ELI.. somebody..HELLP.

i get so many pm's on jetting and carb cleaning... would be easier if they didn't have to dig 40 pages into it to find them...  
Keep it RUBBER SIDE DOWN!!