Timing,vacumme etc..L72

[Jerry Weidner]

Question on settings, I tried setting my intial timing at the factory specs between 8-12 advanced. The car did not run well so I decided to set the timing by reving the car until the mechanical advance was all in and setting the distributor at a total of 38. The car runs much better but now my intial is at around 25 degrees advanced? The car is an L72 with TI ignition. The springs look fairly heavy in the distributor so i do not think I am getting any mechanical at idle. My idle is set at 850-900 rpm's and it idles fine. If I set the timing higher I do start getting some pinging. I run a 50/50 mix of 100 octane and 93.

The other problem I see is that the vacumme can does not seem to be working. When I connect it my timing does not move at all. I am pulling around 14 on the vacumme gauge at full manifold vacumme. My can is labeled B1 and everything was just rebuilt by a local Corvette shop.

Why is my initial timing so high? Should that vacumme can be pulling at that pressure at idle?

The car gets hot but does not overheat as far as I can tell, the temp gauge stops around 200 but I do not know if the temp sender is accurate.

[Jerry Weidner]

Re: Timing,vacumme etc..L72

Sorry s[elled vacuum wrong, never can get that right.

I am running the vacuum can off the ported port on the carb. Which vacuum can should I be using for either the ported or if I convert to full source of vacuum.

Jerry

[Duke W.]

Re: Timing,vacumme etc..L72

Reconfigure the vacuum advance from the OE ported to full time, but NOT until you install a proper spec VAC. Research the archives.

The installed VAC is a boat anchor. The guy who "rebuilt" your distributor is a moron. Like other morons, he has absolutely no idea what vacuum advance really does or how to tailor the vacuum advance characteristics to the specific engine configuration.

Unless you revved it to at least 5000, the centrifugal advance (assuming it's OE) did not achieve maximum, which is probably why the initial ended up so high. You probably didn't rev it high enough to get total. Also, this test must be done with the VAC disconnected.

Full ignition map specs for your engine are in the usual sources.

Duke

[Joe C.]

That's It Duke..................Let

it all hang out. Ahhhhhhhhhhh..........now do you feel better. I have always appreciated your straightforward, no nonsense approach. As you are most of the time, you're dead nuts on.
But, why didn't you chastise Jerry for saying "the springs LOOKED too heavy"?
Why, with that kind of frank talk, you should really join the "other" Corvette forum. You know.........the one with the strange looking shark mascot.

Joe

PS: KUTGW

[Duke W.]

Re: That's It Duke..................Let

I have yet to hear of a "mechanic" or "engine builder" who has the foggiest idea about how to select a proper vacuum advance, but it's not rocket science.

I've explained it a zillion times, and it boils down to a simple one sentence rule.

It seems that "all VACs are B1", yet I have repeatedly said that I do not recommend that one for ANY Corvette engine and have several times posted the part numbers of the three that are matched to the characteristics of all Corvette engines. Then use The Rule to select the specific VAC for the specific engine configuration.

I don't expect all owners to understand this, especially one with only a handful of posts, but "professionals" that are charging 50-100 dollars an hour for labor should be better qualified and more knowledgeable.

You have you own experienced with "professionals" who have their head in a dark place.

And for new users, the archives are your friend.

Duke