I'm curious - which way richens the mix - screwing the screw  clockwise or counterclockwise? when I screwed it counterclockwise was when I got rid of 90+% of my "banging."

As I understand it, this is an "Air Adjusting Screw" therefore if you turn it in you decrease the air to fuel ratio which makes it richer.  If you turn it out the air to fuel is increased which makes it leaner.

Finding the "happy place" in the middle of those extremes is where you want to be.

Under the diaphragm cover on top is where you'll find the fixed pilot fuel jet.

Lancer, old Buddy, "What say you?"

I'm working on the theory that you turn out/cc to correct the factory lean backfire, and if you must go more than 3 turns out you need a bigger pilot jet.  I believe you are actually increasing and decreasing the diameter of a small fuel passage coming up from the float bowl that exits just on the intake side of the throttle valve.

Now..., watch me be wrong on this...   Lancer?

sorry Lancer - maybe it is me being thick - I'm refering to the screw on the side of the enigne nearest to your right leg - the one that people can only get at after drilling out the brass plug. I turned it counter clockwise & got rid of virtually all my backfire. was I richening or leaning out the bike?

thanks for first reply - sorry if I'm sounding confused - would appreciate clarification, Lancer.

from what you said Greg guess my turning it out made bike run leaner, which I thought would not make bike lose popping. however, as it turned out it did. whatever, end result was  

We have what is called a variable venturi type of carburetor.  It has a slide (throttle valve) that goes up and down, and does it either mechanically like in a VM carb or by using engine vacuum like in the stock CV carb.
In this type of carburetor there can be two types of idle mixture control, or even both types, on the carburetor depending on what the manufacturer wants to do.

Air Mixture Screw
On a mechanical slide carburetor, the air mixture screw is always located on the air filter side of the carburetor slide.  It varies the flow rate of the air bleed passageway.  To create a richer air/fuel mixture, you turn the air mixture screw in (clockwise).  This reduces the amount of air allowed to enter the ciruit, creating a rich mixture.  To create a leaner air/fuel mixture, you turn the air mixture screw out (counter clockwise).  This increases the amount of air allowed into the circuit, causing a leaner mixture.

Fuel Mixture Screw
This screw is always located on the engine side of the carburetor slide.  The fuel mixture screw controls the amount of the fuel exiting the idle outlet port.  The fuel mixture screw changes the amount of fuel entering the carburetor while the engine is at idle.  When this screw is turned out (counter clockwise), it enriches the air/fuel mixture by increasing the amount of fuel allowed to enter the circuit.  When the fuel mixture is turned in (clockwise), the mixture becomes lean by reducing the amount of fuel allowed to enter the circuit.  When a fuel mixture scew is used on a street motorcycle, the carburetors have factory-installed anti-tamper plugs over the screw to prevent the untrained consumer (this is a secret code, meaning US) from changing the factory and EPA approved setting.
The stock Savage/S40 carb has the second type, the fuel mixture screw, though it is referred to as the pilot screw in the Parts Manusal (microfich) and Clymer does not address it at all.  The Suzuki Service Manual does not mention it all either.
I have usually used the term pilot air adjusting screw in the past, and if that has confused anyone I apologize.  I just got in the habit of doing that.  A lot of instructions from assorted sources use the same term, but for the stock carb on our engine it is more correct to call it a fuel mixture screw.

On the Mikuni VM carburetors the screw is of the first type, it is an [i][b]air mixture screw, or may be called the pilot air screw[/b][/i].   On this carb turning the pilot air adjusting screw IN (clockwise) will richin the mixture, and OUT (counter clockwise) will lean the mixture.

I hope this is helpful and that I have not confused anyone.  Also, I have a nagging feeling that I may have given incorrect info to a few in the past regarding the direction of the pilot air screw adjustment on the VM carburetor.  If so, then I humbly apologize for that.
There have been occasions when I was getting questions on several types of carbs at the same time and I could have mixed the info from one to the other.  If it did ...I am sorry.

Anyway, the information above is directly from a training manual.  I did not want to try to condense the instructions this time, so I wrote it out as it is printed.  That helps to eliminate problems.

hey georgekathe, the screw you are referring to on the right side, that was formerly covered by the brass cap:

Counter Clockwise to richen
Clockwise to lean out

Rockin_John wrote on 12/31/69 at 16:00:03:


Still exhibiting your extensive array of people skills and other true lies, I see.