What's the proper name of this screw?

[ggreenfield]

In the carb rebuild howto it's called an Air Screw
motorcycle.com calls it a a Fuel Screw
motorcyclecarbs.com calls it a Pilot Screw.
Other places I've seen it called a Mixture Screw.

So what is it really?

[ooqueso]

Not that I'm an expert or anything, but I think mix screw is the best term that I've seen used most. It makes sense, as it controls the air/fuel mixture.

[earlfor]

That is the mixture screw. As already said, it meters the combined air and fuel.

Earl

[argonsagas]

It is not a screw at all. It has machine gauge threads, and it is uniform in shape, so it is a tapered-tip bolt.


On this forum, you should just refer to it as a mixture screw, as everyone will understand it.

[Tarbash 27]

I call it an air screw.

[derwood]

Fredrick or Fred for short

[MelodicMetalGod]

Proper terminology, or lack thereof, is one of my pet peeves.

According to my 83 GS550E/ES factory service manaul, the proper term is "Pilot Screw". That's even the term they used in the carb spec chart. Unfortunately, uniform terminology is not something in effect here and, IMHO, that causes a lot of confusion for all of us. I always try to use factory/manufacturer terminology to ensure clarity, but I've seen several commonly used but incorrect terms used for this part, including:

Air Screw
Air fuel adjustment screws
Air/fuel Mixture Screws
Fuel Flow Screw
Idle Screw
Mix Screw
Pilot Air Screw
Pilot Air Jet
Pilot Jet (this one's just plain wrong as this is the proper name for a different part)


...and, I'm sure, many more.

Bottom line is that there are MANY different terms that are used to refer to the Pilot Screw, so it's up to you to ensure that you and who you communicate with are discussing the same part. Best of luck!

[robertbarr]

I've seen several commonly used but incorrect terms used for this part, including:

Air Screw
Air fuel adjustment screws
Air/fuel Mixture Screws
Fuel Flow Screw
Idle Screw
Mix Screw
Pilot Air Screw
Pilot Air Jet
Pilot Jet (this one's just plain wrong as this is the proper name for a different part)


...and, I'm sure, many more.

... and that's for the CV carbs. It's even worse for the VM, since there are more adjustment screws -- and one that doesn't show up on any factory exploded diagrams. (The mysterious 'emissions screw', with many AKA's). That's why I came up with this scheme:



I need something I can put into an envelope that explains everything, so people can put the correct O-ring on the correct part. I couldn't think of anything more fool-resistant than the alphabet.

[renobruce]

Funny!
On my GS1000 (VM carbs), I call it the pilot mixture screw. On my 1150, I call it the emissions screw. Same thing.

Screwy, huh? Screw it!

[bwringer]

I could tell you what a lot of people call it, especially when it gets stuck, but this is a family forum with filters for bad language... :twisted: :twisted:

[psyguy]

hm, with a number of threads on the gsr we see dealing with carbs it'd be good if we could get the terminology consistent...
to me, and my manual, the screw you're referring to is a (pilot) "mixture screw"

[MelodicMetalGod]

I could tell you what a lot of people call it, especially when it gets stuck, but this is a family forum with filters for bad language... :twisted: :twisted:

Amen, brother! I've got two that merit "questionable terms" right now!

[MelodicMetalGod]

hm, with a number of threads on the gsr we see dealing with carbs it'd be good if we could get the terminology consistent...
to me, and my manual, the screw you're referring to is a (pilot) "mixture screw"

I COMPLETELY agree. Maybe we could start a terminology thread with pics/diagrams?

[KEITH KRAUSE]

On the CV carbs, it's called the pilot fuel screw. Many of us call it the mixture screw because it regulates a passage from which fuel and air are already combined before reaching this screw. Adjusting it outward increases the amount of air/fuel flowing but this WILL richen the mixture entering the cylinder.
On the VM carbs, there are two separate screws. One is the pilot fuel screw. Its purpose is to regulate a mixture of fuel and air through a secondary passage that's part of the pilot circuit. It fine tunes the mixture amount for that cylinder. It "assists" the pilot jet. Adjusting it outward richens the mixture to the cylinder.
The second screw is the pilot air screw or what I call the side air screw. I mention "side" because it leaves no doubt as to which screw I'm talking about when posting advice on VM carbs.
The side air screw regulates only air flow that enters through the air jet.
I also prefer to call it the side air screw because it regulates air for all throttle positions/jetting circuits, not just the pilot circuit. At smaller throttle openings, the air enters the air jet and goes past the air screw and combines with fuel coming up from the pilot jet. This mixture then goes through two passages into the cylinder, one of which is regulated by the pilot fuel screw. At wider throttle positions, the air flow will be directed to the needle jet/main circuit. The needle jet has tiny holes. When fuel enters up the main jet and then through the space between the needle jet and jet needle, the air will flow through these tiny holes to better atomize the fuel. Turning this screw outward will lean the mixture.