how do you adjust timing on a 1969 chevy 350 with HEI distributor without a timing light?
Assuming you can get the engine to run and you can hear high-frequency.
Keep advancing the timing until you can hear the engine "ping"under load, then back it off a little.Turning into direction of rotor travel advances the timing, turning the distributor housing in the same direction as rotor travel retards timing.If you do have the timing to far advanced the engine will not crank properly (it will act as though it is being “kicked back”
This ping will come earlier or later depending on the octane rating of the gas currently being used.
There is a relation between manifold vacuum and engine timing ,since you wont get/borrow a timing light I don’t think asking you to get a text book and read the applicable chapters will be well recieved.
You haven’t said what model the engine is in. Try this link: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152800834e1
All the shop manuals for pre-ESC vehicles had a foot note-‘The correct timing is dependant on ambient temperature, driving conditions, fuel quality and engine condition. Base timing should be set as high as possible without causing pre-ignition.’ Only air cooled engines seemed to be the exception to that rule.