The valve on the line to the intake manifold was called an "anti-backfire"
valve. I don't recall any electrical control for this valve. Rather,
high-vacuum conditions -- which occurred when the throttle was closed at
speed, -- would cause the valve to open, diluting the incoming mixture to
avoid an over-rich condition in the exhaust, which could literally blow the
muffler apart.
It was 1972 when I removed the emission control (Nissan Air Injection
System) from my 1969 U20 before I put it into my 1966 1600. I do not recall
any electrical connections on the anti-backfire valve. I also do not recall
any other "bypass" valve in the system, but mine was vintage 1969, and the
'70s may have had a different design. I still have the complete 1969 NAIS
system -- been in a box since 1972.
Gary
----- Original Message -----
From: "John F Sandhoff" <sandhoff@csus.edu>
To: "peter harrison" <granvillecomputing@hotmail.com>
Cc: <datsun-roadsters@autox.team.net>
Sent: Monday, November 23, 2009 11:23 AM
Subject: Re: [Roadsters] 1970 Schematic
>> Looking at the wiring diagram and on the bottom under the alternator
>> there are
>> two boxes
>>
>> 1 - a) trans switch, b) clutch switch c) bypass valve
>
> Smog control. On the '70s only there's an air valve on the intake
> manifold ("bypass valve"). I forget exact details, but depending on
> what gear you're in and what you're doing with the clutch, as I recall
> it leans out the mixture.
>
> -- John
> John F Sandhoff sandhoff@csus.edu Sacramento, CA
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