Mystery Screw On 3w 106 Carb

[IanB]

Just noticed this and i dont know what it is...........on the side of the carb on the opposite side of the needles is a large diameter brass screw looks to be 4mm diam or so...........anyone know what it does........not a throttle stop guys?

Bueller........? :2aa

[GremlinX]

Can be a casting hole that is filled later with that plug. Or a hole drilled that was used to access another hole to be drilled inside.

[IanB]

well if thats the case they went to a hell of a lot of bother..........i dont think so

[rcign]

The carb came from a chainsaw...The screw covers a ball and a spring...At a predetermined vibration level (very high rpm) the ball vibrates off the spring and lets more fuel into the carb to richen it up and keep the engine from burning up...You will never reach that level unless you tighten up the prop screws against the bottom of the hub and the prop is still a little loose...The screws will shear off and the engine will rev up...

[Xipp]

Well lets see if we can put this to rest.
The screw you are seeing was the stock location fuel inlet,When companys submit a carb order from walbro they give them what they need in a carb then walbro modifies an existing carb to meet those specs. The fuel inlet stuck stright out 3w needed a 90 degree elbow away from the exhaust so walbro just tapped into the fuel chamber with a new inlet and they cap the old one with a screw.

[dick hanson]

The carb is a Tillotson--unless something new has been added -

[dick hanson]

tillotson
Isn't this the carb that came on your 3W?

[rcign]

No way could the fuel inlet have been under that brass screw....

[excelpoint]

i believe Xipp is right that is an alternate fuel inlet(original)

[Boulder]

Ian,

Did you remove the screw and see what is under there? Take it out and blow through the fuel inlet tube. If air comes out the hole, chances are the "original fuel inlet" theory is correct.

[dick hanson]

that is not where they typically put an inlet .
I think if you remove it there may be an small emerald hidden under it -

[IanB]

yes Dick that is the carb so what is the brass crew there next the choke?

A ball and a spring that floods out the engine if thr rpm get too high on the action of vibration??.............I think these things shake the most at idle not at high rpm but perhaps............alternate fuel pick up........if the carb manufacturer mods an existing carb at the instruction of 3w why didnt they mod on a throttle arm!!!!! ...oh and mixture needles that clear the muffler.....the fuel pick up is right there anyway.

Just curious and No I am NOT unscrewing it unless you do first!!

Kindest regards, IanB

[dick hanson]

Ah-- well you passed the test-
I think--it is simply a manufacturing convenience- to allow drilling a passage . -but I have never been into this one so I really don't know.
I will bet you that 3W gets their carbs "by the carton" as is from Ireland - no special ANYTHING on them -
Thes carbs are made by the hogshead for weed whacking/ blowing ,sucking(?) devices of all types and the amount used for model engine is simply a piddling percentage.
This particular carb is purported to have a better midrange - well maybe - I like the Walbro better . I pulled the carb shown, and added a big Walbro to my new ZDZ80 J. They both run fine -I like the Walbro tho - easier to adjust at low end -
For those guys who "leave em as the factory sends em out "- all of this is likely gibberish.

[IanB]

hey Dick if you pulled the carb why dont you unscrew it and see what the heck it is........

RCIGN Id like a good explanation of how the ball and spring work to flood the engine and limit rpm when they shake their ass off at idle??

And if I hear the weight of the ball is tuned to the harmonic resonance of the motor then Im sending you a check just for the sport!!

[dick hanson]

no way - I am saving it to stick on my Evolution 26--