Setting Timing with Vacuum Gauge


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By Nat Santamaria - 16 Years Ago
Hi guys. I know it has been posted before but I can’t locate the thread.

I would like to set the timing using a vacuum gauge. Its a 57 Tbird with a stock 312 and a new Holley 4160 carb.



Many thanks
By pcmenten - 16 Years Ago
I don't know of a specific method, but if that were mine, I'd attach a damped vacuum gauge to the manifold vacuum and then adjust both the timing and the carburetor idle mixture for highest vacuum.
By timmy4 - 16 Years Ago
A mechanic friend once told me you can hook your gauge to the manifold vacume and turn the distributor to the highest vacume and retard the distributor 2 degrees less than the highest vacume raading.
By Gordie T - 16 Years Ago
Try this link.

http://www.classic-cars-online.co.uk/Archive/vacuumgauge.html

By Hoosier Hurricane - 16 Years Ago
You can also set the timing with a tach.  With the vacuum hooked up, keep advancing the distributor (at idle) until you reach maximum rpm.  Then back it off 50 rpm and lock it down.
By oldcarmark - 16 Years Ago
I have tried this method of setting timing with vacuum gauge.It works well but what I found was the timing is quite advanced from the stock settings of 6-10 BTDC.It started fine hot which if it does not, means the advance is too much, and  it ran terrific.My concern is that too much advance can cause motor damage.I have been told to listen for engine knock from preingnition under load but my problem is I don't hear that well.What other mechanical signs can I check for as far as too much advance?I don't think the damper timing marks have shifted but there was certainly more initial advance when I was finished than the factory recommended timing setting.I have since put it back to 10 BTDC until I can be sure I am not damaging motor by running excess advance and someone tells me how to check. 

By the way Nat this will still NOT tell you if your advance mechanism is functioning correctly.Have you done the basic test to see if the vacuum unit will hold vacuum by applying suction to it manually?

By Dan - 16 Years Ago
Paul, what is a "damped" vacuum gauge? Thanks-

oh, and by idle mixture do you mean the air/fuel ratio screws???

By timmy4 - 16 Years Ago
If the timing is too far advanced the engine will over heat also.
By oldcarmark - 16 Years Ago
To set timing with vacuum gauge the engine should be fully warmedup and choke off.Adjust idle speed to specs and adjust mixture to get highest reading on vacuum gauge.Slowly advance the timing until vacuum starts to drop.Back timing off until it begins to drop.Set the timing halfway in between.Then reset idle speed and mixture.Road test and check for preignition under load and engine temperature.Back off timing in increments until knock stops.