[TR] Another Crazy Question: Beware, chestnut related

[terryrs at comcast.net]

>My suggestion would be to first confirm that both the centrifugal advance
>and vacuum advance are doing at least something.  If either one has quit
>working, it can make the engine feel sluggish without actually running
>poorly.  You'll need a timing light to confirm the centrifugal advance :
>SNIP

>For the vacuum advance, you'll also need a MityVac SNIP
>Disconnect the vacuum line from the distributor and hook your vacuum source
>in its place.  Now watch the mark as you apply vacuum.  If it moves at all,
>the unit is probably working OK.  SNIP

>Then set the initial advance using the "road test" method : Advance by 2
>degree steps until you can just barely make the engine knock deliberately
>(by lugging it in 4th gear with it warmed up thoroughly), and then back off
>by 2 degrees.

Lord I love this List!

Nuanced follow up question, then.  I replaced the copper vacuum tube with a rubber tube that fits over that.  Is there a Physics type reason that's a bad idea?

Terry Smith, '59 TR3A
New Hampshire