The Stovebolt Site Forums The Shop Area Engine Shop Timing with Vacuum Guage

I would like to set the ignition timing by using a vacuum guage. I've done a search on this topic but would like to hear from someone who has actually done it. What is the procedure and what should my observations be? I would think that this would be the last step in engine tune up with the valve lash already set. Right now I have the octane selector set at zero and the spark firing at tdc on number 1 cylinder with no vacuum advance.

I know that some use a vacuum gauge to fine tune the idle mix setting on carbs.
It's a great tool to analyze engine condition, but I wasn't aware it could be used to time ignition.

Today's fuel is different from the days the shop manual was printed.
Using the flywheel marks and timing light as suggested will make the engine run too rich.
Generally speaking, a street engine responds and runs best at the leanest setting before harmful pre-ignition occurs.

To find the sweet spot, just keep advancing the dizzy in small steps, until you get a slight ping at wide-open-throttle when accelerating uphill in high gear.
Then back off until the ping fades away.
Works every time and no special tools required.

The engine will respond much snappier at acceleration and you get better milage.
When you are done tuning, read the spark plugs, which tells you how well the engine is in tune and if you have to make adjustments.
Spark Plug Color Chart

This may sound funny, but as a kid with my first car I was not experienced enough to tune the idle mixture by ear. However, my windshield wipers ran off manifold vacuum. So I turned on the wipers and adjusted the idle mixture according to wiper speed. My dad laughed at me but it worked pretty good.

Yeah, vacuum wipers are a great tool, aren't they?

Just gotta keep the windshield lubed with water...