It seems to me that a lot of our forum users don't know how to adjust a carburator . Internet can be sometimes a curse in disguise , to many users are waiting and waiting and then waiting some more for somebody else to write some post with what carburator settings worked best for his bike . It is all wrong , you need to be able to do your own settings , each bike is modded a little different ( or a lot different ) , rides at different altitudes , temperatures etc.
I will now tell you how to adjust your carburator old school style , no internet and facebook involved AND according EXACTLY to your own needs and mods . Of course , you will do the carb adjusting after you do the mod , itīs the last thing you do .
The only special tool you will need is a carburator idle mixture adjusting tool and here you have two options :
1) Buy one from the first MAC , SnapOn , Cornwell etc. tool truck you see ( aprox 50$ ) and no , they are not available in Sears or Home Depot etc.
2) Make your own : Go to the dollar store , get a flathead screwdriver , cut it to 2 - 2 1/2 inches and weld a big **** nut on it ( 9/16 , 3/4 whatever you feel like that day ) . The end result is a short flathead screwdriver with a very short handle that would clear the carburator bowl but will not touch the engine case .
If we have allready the brand spanking new superprofesional tool we may begin adjusting :

a) Adjusting the carburator from 0% to 25% throtle .
The circuit responsible for this is the PILOT JET circuit , it has some air ducts trough the body of the carburator , one of them you can adjust : the idle mixture . Make sure you allready know haw may turns your screw has been turned out : Turn it in untill it stops ( donīt tighten , be gentle ) count how many turns it goes in ( Ex. 1 and a half ) and then turn it out to where you find it ( In example 1 1/2 turns )
With the bike warm ( ride the bike at least 20-30 min before adjusting the carb ) and the engine with more or less at normal idle ( 1300 RPM ) take your shiny new adjusting tool and turn the screw slowly from a quarter to a quarter of a turn ( 90*) , make a few seconds pause in between the steps allowing the engine to stabilize .
Go in untill the engine begins to run unstable , you have reached the leanest point , write down the position , go out untill the engine begins to run unstable , you have reached the richest point , write down the position . Right in the middle of these two extremes is your correct adjustment . If your correct adjusting point is 1 turn or less from the stop your pilot jet is too big , you need to change to the next size smaller and redo the adjustment . If your adjusting point is 3 turns or more out your pilot jet is too small , you ned to get the next size bigger . You need to do this because your pilot jet not only it controls the idle ( 0% ) , it controls also the very first portion off the acceleration ( up to 25% ) . The mixture screw has a double function : it alows the idle mixture adjustment and it can be used as a indicator for the correct size pilot jet .

b) From 25% to 75% you depend on your jet needle to deliver the right mixture .
You could raise the needle step by step untill you have strong acceleration and begin to have some some staggering or hesitation when you close the throtle ( itīs a little too rich ) and then back down one position .
You could lower the needle until it feels slow and flat in the midle , ( you are too lean ) raise the needle one position and repeat . Actually the best adjustment is right smack in the middle of these 2 extremes ( strong acceleration but no hesitation or staggering when you close the throtle ) .

c) From 75% to 100% you depend on your main jet alone and this is the easiest to find : change the main jet step by step ( next size ) untill you get to the one that gives you the top speed on your speedometer ( I prefer an uphill road beacause the wind speed and direction may change but the shape and size of the hill doesn't ) . Use the same road if possible , use the same reference points : Point A and Point B . Do a rolling start in point A at 40 MPH in 6th or 5th . Keep the throttle wide open .

Remember to do one thing at the time ....
For the sake of keeping " A simple guide to carburator tuning " simple I left out some other finer considerations . If there are enough people that already know and have done all of the above and are willing to discuss those finer aspects we will but in a different thread .
Weīll try to keep this one simple .
Please protect your hand when you work on a hot engine .

 

awesome write up dude!!! THANKS

 

Thanke Marcelino, good stuff.

Unfortunately, on the KLX, (with an FCR), there is no way to adjust anything with the carb on the bike. So it turns into a 30 minute ordeal to make on little change at a time... Wish we had a removable subframe.

But the knowledge is much appreciated!
~Steve

 

Carburator adjusting is not hard , itīs just time consuming and a little tedious .

 

Heart surgery is the same way.

 

You could use an old spoke if you have one. Cut to length with the nipple still on, then flatten the cut end with a hammer on the vice. Voila! 1 short flat blade screwdriver. 1 minute mod.

Posted this carb' tuning info a few years back. Pretty much lays it out ABC.

 

Has anybody just said screw it, and gotten themselves an AFR gauge & sensor? I've got an EGT gauge on my 2 stroke sled, it's a great help.

 

For adjusting the idle mixture, I have the Kouba screw installed. It serves a two in one function as both the mixture screw itself and as the tool for adjusting. Very handy! As Marcelino said, just watch those hot engine parts!

One other thing that I have done is to put permanent white paint marks of 1/4 travel increments on my throttle side switch body and one paint mark on my throttle grip. That way it is easy to assess any issues that may arise during either normal riding or testing.

Good post, Marcelino.

 

where's the fun in that??? Any excuse to get in the shed.

YouTube - ‪Carlton Midstrength Beer Commercial [Back Shed Version]‬‏

 

Great write up and reference. I might have to try some of this.

Thanks