The screw is not adjusted by using numbers.

The screw is adjusted by ear.

You warm the bike up, set the idle speed to something a little bit slower than normal, and you slowly turn the screw out and listen for the tone to change and the engine to slow down a bit.....indicating the idle mixture is too rich.  You then slowly turn the screw in until the idle speed increases to the maximum - turn the screw very slowly in, and you might even turn it 1/16" turn at a time and give it a little bit of time to react before turning the screw again.  You are looking for the maximum speed and smoothness - but on the first trial I usually turn it in too far (intentionally) until I hear the engine speed start to decrease - which means the idle mixture is going lean.  If you can turn the screw in all the way and the idle speed does not start to slow down...your pilot jet is too big and the idle mixture is too rich.  (Same for turning the idle mixture screw out....if it goes all the way out and you don't hear the engine slow down - the pilot jet is too small).  Ideally the best idle speed and smoothness should occur with the screw at 1.5 turn.....if it takes 2 that is acceptable.  If the best idle speed occurs at less then 1.5 turns put in a smaller pilot jet....if the best idle speed occurs at more then 2 turns put in a bigger pilot jet.

The reason you turn the idle speed down a bit is that if the idle speed is too high it could be pulling the vacuum operated slide up a bit - and it will be letting in fuel that will alter the adjustment you are making.  Also it is easier to hear the changes in the mixture screw adjustment.

When you have the mixture screw set correctly you can then adjust the  idle speed screw for the idle speed you want.  If you find the engine makes a bit too much popping for you then try turning the idle mixture screw out just a bit - but if you have to turn it more then 1/2 turn....try the next larger pilot jet.  However you should not place the priority on the pops and backfires - the bike just does that - you should place the priority on what makes the engine run the smoothest and get the most mileage.  Too big of a pilot jet and the mileage suffers horribly.

The plug reading has very little to do with the color of the spark plug.  Most riding is done with the throttle open far enough that the slide needle and main jet is the controlling factor on the color of the spark plug.  What have you done with the white spacer?

Yoshi wrote on 06/07/14 at 06:58:52:


You don't jet the bike to eliminate backfires......you jet the bike to allow the engine to run with the proper mixture.

You use your right hand on the throttle to control the backfires as best as you can.  If you close the throttle completely when slowing down or shifting it will backfire.  If you hold the throttle open just a tiny amount, you can eliminate most of the backfires.

I knew the bike was lean because it wouldent cruise on the highway, I knew it needed more fuel

It would backfire real bad too, and a loud poof on shut down

I use to tune motors so I know the lean/rich feeling