Can someone explain which way to turn this screw. I am a little confused with all the old posts...

If you are turning it clockwise or in you are doing what? Making it leaner or richer???


Thanks!!!

 

Clockwise makes the idle leaner. It only affects the idle mixture (and off-idle slightly). Off idle is where the throttle is just barely cracked open.

You have to shim the needles to richen off-idle to 1/4 throttle, and change jets for 1/2 to full throttle.

 

Think of it this way
If its called an air screw(mostly 2 stroke motors), out is more air,more lean.
If its called a mixture screw(mostly 4 stroke motors)out is more mixture, more rich.
Read more about it here.
carb 101

 

Thanks for the link, very helpful..

What my problem is, is that my spark plug is realy rich and full of soot. Do I need to rejet or is there a way that I can lean it out w/o jetting???

Also I get a backfire out of the exhaust once and awhile after being full throttle and letting up off the gas? Woud this be caused by being rich?

Thanks!!!

 

Hondabuster, we have been calling it an air screw (some of us). Out is rich in is lean. Every two stroke carb I have owned or worked on is the same way too. In=lean, out=rich. In fact every carbureted car I have worked on has had one just like it. Never seen one go backwards.

The air screw actually uses an air circuit to siphon gas with it. It is extremely rich by itself. That is why turning the screw out gives you more gas. Mix that air screw flow with straight air from cracking the butterfly open slightly and you have an idle.


BabyMoose, according to the plug experts, you have to run the quad for a minute at 1/2 throttle or higher then kill it before letting off the gas. Then take a plug reading.

Also according to the plug experts, you cannot use a plug reading to adjust needles or the idle mixture.

Adjust the idle by listening and turning the screw until it is 1/4 turn past the point where it idles fastest. Adjust the needles by how it runs when hot vs how it runs cold at 1/8 to 1/4 throttle. Adjust the mains by doing a plug reading.

the backfire might be the idle setting is too lean. Lean idle causes a misfire when decelerating. the next fire ignites the unburned exhaust and makes a loud pooping sound. Rich idle does not misfire.

 

Nyroc, thanks for the great advise as always.

I took my reading by running it up and down the road a couple of times and took the plug ready instantly.

As far as the backfire you are saying the idle is lean, so I would then open the air/fuel screw and that should increase the fuel for the idle? Or do I just turn the idle screw so it idles @ a higher RPM...

I know... rookie questions...

 

Adjust the mixture screw out, for a richer mixture, then you might have to adjust the idle.Here are a couple of sites explaining how its done.
carb tuning
more
carb


nyroc,
Ive worked on many two strokes, but maybe i didnt word it correctly, what i meant to say, If the mixture screw is on the atmospheric or inlet side of the carb, it meters air and turning it out will lean the mixture. If it’s on the outlet or engine side of the carb, it meters fuel and turning it out will richen the mixture. But youre right, some 2 strokes have mixture screws.

 

Hondabuster, the problem here is terminology. Someone falsely began calling the idle mixture screws, air screws which they are not and the term stuck. The air side screws that work in reverse of what everyone here seems to be familiar with are usually called air bleed screws. When turned left they open an extermal air port which decreases internal negative pressure and causes the stream to pick up less fuel causing a leaner mixture.

Air bleed screws are used as you have stated on some 2 strokes and a lot of foreign cars. As i said before, someone decided to change terms without reguard to the facts. What we deal with on the Prairies and the Vs are idle mixture screws and not air screws.

 

Kind of like , calling the enrichener a choke. I remember chokes, and they worked much better than an enrichener. Thanks for the clarification, dangerous.

 

You need to re-jet. Your jets are too rich. The reason you get the backfire is there is unburnt fuel in the exhaust that's burning later (the actual backfire).