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GMC Jim · 08-05-2003, 05:50 PM

Timimg specs for a 1971 250 Cu. in. 6 cylinder are. (Centrifugal Advance/ Degrees @ engine RPM)----0 @ 930; 2 @ 1270; 14 @ 2300 and 24 @ 4100. Vacuum advance ( in Crank degrees ) 0 @ 8" vac and 23 @ 16" vac. Initial ignition timing at engine idle is 4 degrees.
Another GM reference manual "1971-80 Tune up Specifications" states that the combined centrifugal and vacuum advance should be in the range of 30 to 38 degrees at 2000 RPM. This is easy to accomplish using an adjustable timing lite.
Recomend to install new spark plug wiring harness compatable with the higher HEI produced voltages and new spark plugs gapped at .045.

08-05-2003, 05:50 PM	#6
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	Timimg specs for a 1971 250 Cu. in. 6 cylinder are. (Centrifugal Advance/ Degrees @ engine RPM)----0 @ 930; 2 @ 1270; 14 @ 2300 and 24 @ 4100. Vacuum advance ( in Crank degrees ) 0 @ 8" vac and 23 @ 16" vac. Initial ignition timing at engine idle is 4 degrees. Another GM reference manual "1971-80 Tune up Specifications" states that the combined centrifugal and vacuum advance should be in the range of 30 to 38 degrees at 2000 RPM. This is easy to accomplish using an adjustable timing lite. Recomend to install new spark plug wiring harness compatable with the higher HEI produced voltages and new spark plugs gapped at .045. __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).