To 'A',
No, it's the opposite of what you repeated back. As Mike says, on carburetors
where the low speed mixture screw is located in the air bleed passage: "By
turning the screw 'in' (clockwise), you decrease the amount of air in the pilot
passages which makes the mixture...." ...not leaner, but richer. Mike said
'leaner' when I think he meant to say 'richer'.
But on carburetors where the mixture screw is located in the passage between the
low speed jet and the idle fuel discharge orifice into the venturi, the screw is
controlling the flow rate of aerated fuel delivered to the carburetor
bore...turning the screw 'outward' (CCW) on those carburetors allows more
aerated fuel to flow thru that passage, making the mixture richer. Constant
velocity-type carbs that I've seen, such as those used on the Honda CB/CL360,
are this way. (And the mixture screw location on these is more toward the
'downstream' end of the carb instead of more toward the 'upstream' end.)
John K
in Indiana
________________________________
From: A <ak6666666@yahoo.co.uk>
To: Honda-C70@yahoogroups.com
Sent: Fri, August 5, 2011 2:22:38 AM
Subject: [Honda-C70] Re: mixture screw working
Thanks a lot.
So screwing in makes fuel leaner, out, richer. Got it. Thanks.
--- In Honda-C70@yahoogroups.com, Mike Gladu <mgladu@...> wrote:
>
> At 5:26 AM +0000 7/27/11, A wrote:
> >I don't know what happens when we screw in the mixture screw. Does
> >it increase the gas or air content? Makes it richer or leaner?
>
> The pilot screw on a Keihin side-draft carb changes the amount of air
> that passes through the internal carb passages to mix with fuel in
> the "slow" circuit.
>
> The result may be counter-intuitive to some, but bear with me while I explain.
>
> The pilot circuit in the carb is there to make the idle and
> low-to-mid throttle opening mixture (air and fuel) fine-tuneable
> beyond what you get with just a fixed jet size and the throttle stop
> (idle) screw setting.
>
> By turning the screw 'in' (clockwise), you decrease the amount of air
> in the pilot passages which makes the mixture leaner.
>
> The opposite is true when adjusting the pilot screw 'out' (CCW).
>
> The adjustment has to be done with the throttle slide slightly raised
> (idle elevated) in order to balance the extra fuel and air delivery
> across the transition between idle (slide closed) and open throttle.
>
> Mike G.
> -
>
[Non-text portions of this message have been removed]
1970-73 C70 Honda Service Manual: http://tinyurl.com/6ebwtw
1970-73 C70 Troubleshooting Guide:
http://tinyurl.com/6ebwtw (scroll to sec.7.1 page 101.jpg)
1980-83 C70 Honda Service Manual: http://tinyurl.com/hu42c
1980-81 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec.18-1 page 170.jpg)
1982-83 C70 Troubleshooting Guide:
http://tinyurl.com/hu42c (scroll to sec. 20-28 page 205.jpg)
1980-81 C70 Maintenance Schedule: http://tinyurl.com/z4zn6
1982-83 C70 Maintenance Schedule: http://tinyurl.com/hw35c
More resources for C70 Passports and Cubs:
http://www.shlaes.com/Vehicles/Scooter.htm
http://www.velodrome.com/HondaC70/HondaC70.html
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