Im setting the timing first (swapped to a mechanical dizzy) before I can adjust the new Holley Carb, and I see on the emissions sticker, the factory setting for timing is set at 6 BTC (dr) Whats dr??? see link below to view the emissions sticker.
http://www.classicindustries.com/pro...ts/dc1347.html

 

In drive perhaps?

 

Ummm... Have you ever tried adjusting the timing on a car while it is in drive? I dont care what that sticker says!

 

Set the timing to 12* btdc at idle in park with vac advance line un hooked. The engine will run better and smoother, more off idle response, more power. Hook vac advance line up to full manifold vac port on carb, not the timed or ported one.

 

Funny you say that. Thats exactly how im used to doing it (been a while though) on older 350's that were non computer controlled HEI. This old 1983 305ci is the worst ever made by GM though im thinking...it is the LG4 low compression, 145HP, gas eatiN beast...lol If I try to set initial timing 12* BTDC it doesnt like it....for whatever reason. Following the emissions sticker that I found on classic industries web site (mine is missing) for year model 83 it shows 6* BTDC....and seems to like that allot better.....but Im still playing with it. Its a little bit of a guessing game too with a new carb on top that is not fully adjusted yet. I adjusted the float bowls using the old bump the fender method to get the fuel level even with the bottom of the site plug, but thats about it for the carb for now till I get the timing right. What bothers me is that I went ahead and locked down the dist. set at 6* BTDC and it doesnt knock, ping or puke out of the carb so i know im close......but my vacuum guage only shows 16, which if I remember right indicates late ignition timing...

 

Oh, meant to say, I agree about hooking dist to full manifold vac. Def will do that. Another question however is that this dizzy has an adjustable vacuum canister on it. Never dealt with those before. How do you know how much you need to adjust in or out on the screw? I just opened it to what Im guessing is about half way and crossed my fingers...lol

 

stock settings have no bearing, might as well just forget it. 8-12 for a stock engine is probably going to be what it likes. do yourself a favor read the distructions on the dist for adjustments, depends on what you bought what you need to do. then read the holley tuning sticky on here its pretty good. its sort of a back and forth process once you have it running i would set the idle timing then the idle mixes on the carb. then you can tweak the idle timing to where its happy, number doesnt matter. then advance adjustments, then i would go through the carb tuning. you can always go back and forth to dial it in.

 

Timing and fuel economy is near perfect currently. Initial timing after back and forth from distributer to carb is set at 8* BTDC . Any more than that and slight pinging occurs on this particular engine for whatever reason. Total advanced timing was in typical range ( don't remember actual spec since there has been sleep since then) and timing curve is aggressive since I switched the springs

 

The adjustment for the vacuum diaphragm is still a question however.... And "read the instructions" is not an answer as it mentions NOTHING about how much advance it should offer, and only states that it is adjustable. Nothing more said about it. So I just did what any common sense mechanic would do… hooked up a vacuum gauge and adjusted out the vacuum setting until it was in the normal range of about 17 to 20 inches of vacuum at idle and locked er down. Good to go.

 

Sorry, I should also say that I was doing all of this with the vacuum gauge and the timing light at the same time and adjusting mixture screws along with vacuum diaphragm on distributor, all the while watching how much advance it offered at idle (without readjusting distributer as initial had already been found) and watching vacuum gauge to get everything in normal range. It was a lot of trial and error but now seems to be running great.

 

you never said what the dist even was, to me mechanical is just mechanical no vacuum, there are a million hei's between aftermarket, stock, upgraded stock, etc.... so read the instructions is the only valid advise you can give with the vague description you gave.

i have a mallory race setup, its a hei and is completely different on adjustments, i imagine msd is the same.

from msd as to what a vacuum can and adjustments do;

Vacuum Advance

Vacuum advance is primarily used in an effort to improve economy, therefore you won’t hear much about vacuum advance when discussing performance and racing. There is little to no vacuum during wide open throttle which means no vacuum advance any way!

A vacuum advance canister provides a way to advance the ignition timing during moderate and part throttle conditions. This is when the load on the engine is less and vacuum is higher. There is a diaphragm inside the canister which is connected to a linkage connected to the pickup plate in the distributor. When vacuum is applied, the plate is pulled which advances when the trigger signal is created. When the engine accelerates, vacuum drops so the advance returns to the original position.

When connecting the vacuum advance, most applications connect to a port above the throttle plates. This is called ported vacuum compared to manifold vacuum which comes straight from the intake manifold. The difference here is that manifold vacuum is there constantly while the ported source provides vacuum only when the throttle blades are open. The amount of advance that occurs varies by application but generally ranges from 10°-15°. Some companies even offer an adjustable vacuum advance canister. This lets you set the exact amount of vacuum advance that your engine requires.