Re: 1974 Sonett III - static timing - Saabnet.com Bulletin Board


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Re: 1974 Sonett III - static timing
Posted by Jim H (more from Jim H) on Thu, 3 May 2018 18:50:23

In Reply to: Re: 1974 Sonett III - Installing a Manual Choke on a FoMoCo carbureto, juanm [Profile/Gallery] , Thu, 3 May 2018 05:31:15
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Your very welcome juanm.

Here is Jack Ashcraft's method for timing the V4:

Set the timing with a strobe light attached to the no. 1 cylinder's
spark plug wire. (No. 1 cylinder is the one behind the alternator).
Disconnect the other 3 spark plug wires from the spark plugs. Disconnect the hose from the carburetor to the vacuum control unit. If your car still has the hose from the plate below the carburetor to the second connection on the vacuum control unit (for RETARD) disconnect that hose also. Have a friend turn the engine over. Set the ignition timing at six degrees before top dead center(See the raised marks on the timing cover). Loosen the bolt at the base of the distributor and rotate the distributor as required to set the timing at six degrees. Re-tighten the bolt. Re-check the timing--it should still be at six dgrees BTDC at cranking speed.

The REASON for setting the timing at CRANKING SPEED (instead of at IDLE
SPEED) is that a lot of Bosch distributors pick up MECHANICAL ADVANCE
as low as 300 distributor (600 engine) RPM. Normal idle speed is 1000 rpm. You can have as much as 5 degrees advance at 1000 RPM under these conditions. If you then set the timing at WHAT YOU THINK is 6 degrees, you will actually have 11 degrees. Too much initial advance and too much MAXIMUM advance can cause pre-ignition (pinging) and a lot of heat build up in the cylinder head, to the point that you can burn a hole in the crown of the piston--right below the position of the spark plug.

So set your timing at 6 degrees BTDC at cranking speed. Then hook
everything back up and CHECK it at idle speed. You will quickly see what your distributor is doing.
Jack Ashcraft


Also juanm check your distributor lobes which open and close the points for wear and the shaft inside the distributor (lobes sit onto shaft) for side to side wear/wobble which will affect the timing (dwell) if worn.

posted by 24.66.1...

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