Mike---It does seem odd that Triumph manuals do not show the vacuum
readings for the carbureted engine. One would think there could be a
chart for the various stock cams, or something.
Anyhow, this is the vacuum readings I've found by testing some of the
different cams, with the test engine is decent
shape:
At idle speeds of 850 rpm. Stock grind with the 18/56 valve timing....19
inches
Also a stock choice, early engines,
Idle at 800 with the 10/50 ....20 inches
Idle at 900 with the S-2 cam....12 inches
Idle at 900 with the Isky Z-19....13 inches
The bigger the overlap, the lower the vacuum signal.
Ignition timing comes into play when taking a vacuum reading with all
cams. I set the timing at 10 deg.BTDC to keep this variable out of the
picture.
I doesn't sound like you are dealng with a vacuum leak, per se. To get
the engine to idle better with your cam, at lower engine speeds, you may
have to go with a richer fuel/air mix, or dial in more ign. timing
advance. If your cam has more duration and overlap than say the S-2, the
engine will be happier with idle speeds at or over 1,000 rpm.
Dick
Mike wrote:
6pack@autox.team.net Subject: Manifold vacuum pressure
I cannot find in any of my manuals the vacuum pressure value at idle for
a carburated engine. Actually I need to know what it is at 1000 RPM as
my more aggressive cam won't let it idle at 850. Does 12 psi sound about
correct? I'm trying to find out if my non-functioning retard capsule is
defective or if I have insufficient suction. Thanks in advance. Mike C
'71 CC62976L
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