69 Z28 Timing

[Plowman]

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Vacuum advaance should be no more than 10 degrees. Paul

[/ QUOTE ]I'm not saying you are wrong but how did you come up with the 10 deg.figure for a max ?

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I learned it at school 40 years ago, but I have found it to be true throughout the years.

Some vacuum advance units pull 20 degrees. You have to check it out with a timing light. Each engine has varying vacuum at idle depending on the engine, cam shaft, etc. 10 degrees is what I found to be a good idle. Any more than that and you get really rough idle from over timing. 10 degrees of VA at idle means you can adjust the idle mixture screws to run idle leaner so you don’t load up or get puddling of fuel at idle.

VA for street use is for fuel economy. So, as you hit the accelerator you lose vacuum. When you are off the accelerator you have vacuum advance.