A high vacuum level under power will also shut down your power system (pull the metering rod down, or close the power valve) and lean it out.
And the only way to really check it out to to rig up a vacuum gauge and do a few test runs.How many guys messing with engines actually do this,probably very few.Some spend a lot of time looking for high speed misfiring or power loss,and they might be looking in all the wrong places.
The limited vacuum advance running off the intake is more often than not used on cammed up V-8 street engines.It almost always has a positive effect on part throttle performance.
It's simple to do and worth a try .........
