What happens in those carbs of ours, airflow/fuel wise?

Let's see
starting from engine-end we look into the carb
and first we see the pilot outlet
witch lets in fuel regulated by the pilot screw


right behind it (not visible on photo)
we find the bypass ports








Next are (left) the outlet controlled by the main nozzle
and (right) the outlet controlled by the jetneedle attached to the vacuum piston.

So what causes the fuel to flow into this space and on into the
engine?
Well, because the diameter of the passage through the carburetor
lessens right here, constrictting the passage of air; the venturi effect comes into play
and causes fuel to be sucked into the venturi.

Now how is this vacuum thing working for the vacuum piston/needle.
Same thing:
Take a look at the piston/(and needle)




or seen from 'inside' the vacuum chamber, through the piston anddown into the venturi (blue light inside venturi):



so here we have tree holes to be sucked at !
yeah, but no fuel or anything in there to be venturi-sucked out through those holes, you might say?
Oh yes; air will be sucked out, in effect creating a vacuum inside
the (surprise) vacuum chamber

Take a look here:



DARK blue is air being sucked out through the holes in the piston
Yellow is the vacuum thus created.
Note the small air passage right under the space
to witch the white plastic thingie forms the top 'lid'.

This drawing shows the situation with the trottle valve (right side)
1/4 to 1/2 open.
(PS: LIGHT blue is fuel)

What happens is that when you open the trottle more and more
---> more and more air sucks--->more vacuum--->
piston is moved upwards because of the vacuum--->
more air AND fuel is lead into engine (jet needle, controlling
fuel rate is attached to piston..remember)

(for more on what happens when, please look
at this, and the pages following)

Now back to that tiny air passage at the top of the
vacuum chamber (here back-lit through the pastic thingie



as you can deduct from the drawing shown above this passage is
needed to 'vent' the space created by the hollow piston 'rod'
and the tube in witch it slides (also shown here back lit through
the plastic)




so yes; you are in trouble if your plastic thingies are not intact.
Not only will the air passing through a hole in the plastic,
lower the vacuum in the chamber, and thereby in effect
lower the position of the piston (lowering the intake of fuel/air)
but 'false' air will enter through
hole--> vacuum chamber--> holes in piston--> venturi-->engine

Not good.


Still don't believe me ?!

For the sake of investegating this facinating subject
I put my health at risk and lit up a cigaret
..grabbed a vacuum chamber with a holed plastic top
..inserted a piston/needle (a bit of tape to make up for
slack in piston/side of chamber)
..and blew smoke into the hole



yes indeed; the smoke passed

hole in plastic--> vacuum chamber--> holes in piston-->
(and would pass on to; venturi-->engine)


Conclusion: replace chambers with defect plastic tops.


BTW another thing came up:

The plastic thingie does in fact act as a
upper-level-stop for the pistons.

Not only are traces of the piston rod/tube clearly visible at the underside of the plastic:



but I did measure vacuum chamber-tube/piston-rod/
piston etc. to confirm this.



Facinating stuff...right?

_________________
Da' Supercharged Bulldog



"A designer knows he has achieved perfection
not when there is nothing left to add
but when there is nothing left to take away"

Antoine de Saint-Exupery

Glad my 1100 does not have plastic tops, think that's why Honda changed them?

Nicely done ... again.

_________________
"5 year survivor bi-lateral lung transplant"
"Live Long, Ride Free"
"Life is too short to work all the time ... get out and ride"
"Integrity is doing the right thing when no one else is watching"

1982 GL 1100

1972 CB 750 K2 SOHC
1973 CB 450 K6 DOHC
Member AMA

ah. aah-hah. hmm.

now if, say, I've removed the white, plasticky button thinga-ma-jiggies, and covered the tops of the CV piston housings with something else... [insert round object here] does the volume of the vacuum chamber have an effect?

following a Randakk rebuild, meticulously adhered to, even weight balanced the slides on a gram scale. I might have installed my [round objects] too low on the CV piston housings to allow total upward movement of said piston.

2 reasons I ask, I'm having "some" issues, mostly at idle which is likely not relevant to this, but I'm getting some "chuffing" on hard throttle at higher RPMs.

and also 'cause I like to know more stuff about GoldWings.

_________________
bulldogged 1978 GL1000 - "geekster" - daily rider
full dress 1979 GL1000 - SteamPunk Barge - daily rider
"found" a 1978 for $100
got another "new" 1978 from a member here
and my original '79 parts basket case.

A gentleman is one who puts more into the world than he takes out. ~ George Bernard Shaw