GMC 250 Inline 6 Tuneup

[RichardJ]

>>I did set the points gap to .019. Just curious, why set initial timing at 10 degrees? I thought timing on these 250's was 0.<<

The reason some are suggesting a Dwell meter is because many have trouble setting .019" accurately. It takes a delicate touch. Without knowing your skill level, you should understand that many guys are ham-fisted and will end up with a gap much smaller than .019" without realizing. It's best to pull the feeler out of the set and hold the single feeler.

Any change in the dwell will move the timing mark, so dwell must be done first.

Timing 2nd.

Idle speed 3rd. Set idle speed screw to 600 or as close to 600 as you can.

Adjust mixture screw. Readjust speed screw back to 600. Readjust mixture screw if needed.

Set the timing to 0 or 10 as needed? If it pings @10, retard the timing. If you start driving with the timing @0 , you can experiment by adding a couple degrees each time you drive it.
If it pings when you lug the engine, don't lug it, downshift, or get higher octane gas, or retard the timing a couple degrees, or all the above. Just don't let it continue to ping. Downshift.