My Chiltons manual reads 1967-1969 SRL311 ( 20 Degrees) @700 rpm
-----Original Message-----
From: John F Sandhoff <sandhoff@csus.edu>
To: andycost@att.net <andycost@att.net>
Cc: datsun-roadsters@autox.team.net <datsun-roadsters@autox.team.net>
Date: Wednesday, April 04, 2001 5:15 PM
Subject: Re: vacuum advance
>It was asked:
>> How many degrees does the vacuum advance timing?
>>
>> What would happen if the timing was set to 0 or less
>> degrees static and then hook the vacuum line to the
>> manifold?
>
>Repeat after me: no no no no no no no.....
>
>That is NOT how the vacuum advance works.
>Full WOT advance should be about 30 (maybe 35) degrees. More than
>that and you get detonation and destroyed pistons. I believe a couple
>other list members can attest to that?... :-)
>
>So the idle (there's no mechanical advance at idle if the distributor is in
>good order) should be: 30 degrees minus amount of mechanical
>advance. A pre-smog distributor has 15 degrees advance (7.5 degrees
>of CAMshaft advance=15 degrees at the CRANK). 30-15=15.
>Hey - pretty close! An SU car should be set to 16 degrees BTDC and
>a Solex at 18 degrees.
>
>A smog distributor is 15 degrees cam, 30 degrees crank. 30-30=0.
>Yup: smog cars get set 0 BTDC which is why off-the-line performance
>sucks, errr, I mean, is poor. Give it a few degrees advance and it'll
>run MUCH better. It'll also melt a piston pulling a hill :-(.
>
>The vacuum advance affects the timing during PARTIAL throttle. At
>WOT you have no vacuum advance, at idle you have no vacuum
>advance. In the middle, you can advance past 30-35 degrees because,
>well, that's just how an internal combustion engine works...
>
>The vacuum line goes to the carburetor vacuum port. (On a smog
>car, it routes thru a temperature switch. When the engine starts to
>overheat, it adds advance. Different topic...). Any other routing is
>incorrect.
>
>BTW, Solex carbs do not use the vacuum line.
>
>-- John
> John F Sandhoff sandhoff@csus.edu Sacramento, CA
>
>p.s. When you take apart the distributor, the advance plate will
>have either a 7.5 or a 15 stamped on it. Now you know what that
>number means!
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