Dizzy vac question [NEW DISCOVERY]

[texas_bugeye]

Well I got the jetting pretty much sorted out on the DGV no hesatation winds straight to the top.main was a little lean. Now these questions comes up
1 Does a 25D clone with pertronix shutter dizzy need manifold vacume or does it need carb / port vacume? hmmm...
2 check timming with vac disconnected ?
3 How much advance?

NEW FINDINGS
Well I put in the new dizzy got the car started and running fairly well. I took it out for a drive and started experementing with the timming. I put in more advance with the vac not connected and the cab port plugged.
Runs strong and is more crisp.So I added alittle more advance <u>now get this </u>it developed a small leak at the tappet cover what the ??
Went home cleaned it up and pushed the advance back to where it was prior to the leak. I took it out for another run and presto no leak! So it must develop crank case pressure at the setting with alot of advance there really was no performance gain or loss at the high advance but it does have more crankcase pressure. So what heck would cause that and is it a concern.

 

[Morris]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]So it must develop crank case pressure at the setting with alot of advance there really was no performance gain or loss at the high advance but it does have more crankcase pressure.[/QUOTE]

Taking a wild guess here... cylinder bores can be greater at the bottom than they are at the top. If you are over advanced, you could be igniting the fuel at the low enough in your stroke that the rings do not have as good a seal as they do at the top.

Did you hear any "clacking" when you had the ignition advanced? If you were getting "knock", perhaps this could be blowing pressure past your rings.

You may also consider checking for a blown head gasket. The correlation between spark advance and your leak may be coincidental.

 

[JeffS]

Chris, always use ported vacuum if you can. Almost all of the aftermarket distributors come with a vacuum advance for ported vacuum. You should be somewhere between 10-14 BTDC at idle without the vacuum advance hooked up, right? The hook it up and the setting should stay the same.