Clear this up for me please.

[WOJO 1]

I read on web site a phrease that has me confused. It stated "On a 2 stroke the idle/mixture screw is an AIR screw not a Fuel screw". So when you go counter clockwise you increase air and decrease fuel? Which is correct? Thanks

 

[funk6294]

Re: Clear this up for me please.

I believe it really is a matter of the carbuerator type. Just saying because it is a two stoke that it operates that way may not be entirely accurate. Below is an exert from an article Greg Hall wrote on rejetting motorcylces, but the information applies here just as well.


"IDLE MIXTURE SCREW:
The idle mixture screw is the only externally adjustable carburetor jet available and controls up to 1/8 throttle only. There are two types of idle mixture screws. One type is called a fuel screw because it regulates the flow of fuel into the idle circuit. This type of screw is located ahead of the carb's slide tower (motor side) and is most often found under the carb's bore and upside-down directly ahead of the carb's float bowl. By turning the screw out you increase the amount of fuel that is allowed to slip around the tapered needle and into the carb's bore where it is mixed with air that has snuck under the carb's slide.

If the idle mixture adjustment screw is located behind the carb's slide tower (airbox side) then the adjusting needle regulates air flow into a fixed flow of fuel intended for idle. By turning this screw inward you are reducing the air flow, thus richening the idle mixture.
When the motor is up to operating temperature, set your idle speed screw to a stable idle. Then use either your idle fuel or air screw to obtain a stable idle. Reset the idle speed screw as necessary after obtaining the correct idle mixture."
"

 

[j_martin]

Re: Clear this up for me please.

It all depends on the carb. On a merc V6 2bbl carb, the idle jet (which is the only adjustment on a WH carb) measures air, so larger is leaner. The mains measure fuel, so larger is richer.

If you have an adjustment, it's pretty easy to discern the adjustment. From peak speed, going richer makes it run smoother and slower. Going leaner makes it miss, then stumble, then fail, all with a rather small adjustment.

Most high performance 2 cycles need to run fairly rich to avoid damage from high cylinder temps.

hope it helps
John