Well I tried the vacuum tuning method today and I am not sure I understand the results: Setup is an L-82 top end rebuilt,orig timing chain, orig L-82 cam, automatic trany. I connected to the vacuum supply for the headlights at the port near the back of the intake. Turned the dist to acheive max vac.

In Park, vac advance plugged, 13" +-.5 @ 950RPM

In Park, vac advance connected, went to 15" +-.25 @1050RPM

In Drive, vac adv connected, went to 10" +-1 @800RPM

1) Why do my vac numbers seem so much lower than other folks? L82 cam? Is this Normal?

2) Is the drop in vac from Park to Drive of 5" Vac normal?

3) Seemed like I could turn the dist as far as it would go counterclockwise and it would still run OK with around 15" vac. Doesn't seem right?

FLA VETTE38731.8478240741

You're turning an L-82 to 10,500 rpm? That might be your problem!
A healthy, normal engine should produce around 20/25" of vaccuum at idle. You hit on something that might be trouble in your post."ORIG. timing chain".

Agreed, the timing chain has been on my list.. this is also something I haven't tried before but maybe I should...

Had some more time to tune today...

Started adjusting fuel air on the QJET using the vac reading, started at 3 turns out with the results as shown above. After adjusting, ended up at 10.5 turns out on each side, vac 18, RPM 1050 park no advance connected. Connected advance, all parameters were the same except vac now 18.5. All looks good, idle has never been smoother, ran good during first drive. When I bring up the RPM over 2000 the vac is 20.5" steady. The reason I am tuning to 1050 RPM is due to the drop in RPM when I put it into drive which puts me around 750-800. Much better or am I missing something?

FLA VETTE38731.8502662037

TEN THOUSAND, five hunnert RPM???!!
You sure you don't mean 1500?? (Fifteen hunnert rpm?)
You should be idling, in drive, at around 700 rpm, I think. Does your car still have the emissions decal under the hood? It will tell you at what rpm it should idle. It may actually be closer to 600rpm.
It sounds like you are getting closer to the optimum tune on it. Good job!

can you say "EDIT"? Adams' Apple38732.3448958333

Hi guys ,

tried OF COURSE also your method of vacuum timing.I got 18" vacuum at 750 rpm.Checking this with timing light gives 12° static advance.

Joel, you mentioned 20" to 25" but a 'hotter' cam or big carb results in a bit less vacuum i think.( Hope my engine is still healty .... )

Now i installed ( ACCEL) new heavy spring breaker points , centrifugal weights with set of springs to choose  and adjustible vacuum advance kit. I start with 12° static , 24° centrifugal coming between 800 and 2800 rpm and the vacuum restricted at 10-12° but coming in as soon as possible ( most less spring tension). Perhaps this evening i try.I keep you posted !

 

I have never seen anything stock idle at 25 in. vacuum.  And our engines would be doing really well at 20.  That 18.5 is actually quite good.   Keep in mind for every 1000 ft over sea level you reduce your vacuum by 1 inch.  How high or low are you Norbert?  You will find that if you finish about 38 deg at full advance you are in the ball park.   Mine presently runs best at 35 BTDC full advance under load.  This took a bit of playing on a dyno.

If you go back in history post, you can find one that is a total pain to perform, but will allow you to tune the timing to almost perfection.  The procedure was posted by Ben - Chutula.

You may also want to peak the vacuum at idle with the mixture screws.  You want them in as far as possible with the vacuum as high as possible.  Then go back to the timing.  If you need to make large adjustments, go back and forth a couple of times to get a good balance.  You'll like it.

What ever happened to Ben anyway?

kstyer38754.8641666667

I went back to stock original....  as it "was".Couldn't get it better and even worse as in acceleration there where always some pufpufs..

It was fun playing with it but find :

1) the Accel mech advance kit is of dubious quality : the weights are exact the same as original and weight 35 gr ( for the 2 ) also exact as originals but the accels are just rough punch out metal , the pivoting holes not even perfect.Originals are smooth and with exact holes ! Then there are 3 sets of springs : everybody over here sees a black set, silver and gold ones.Oyeah , in there manual leaflet they speak of  white, blue and red ones... 

2) the adjustable vacuum advance from Crane Cams....Nice , it fits and the leaflet explanes how to adjust but never mention how many degrees from min. to max. you can adjust. Originals are giving as 12° or 20° depending on what type distributor.And there's a limiter plate to place under the screw inside so limiting the max vacuum advance ( in surplus with the adjustable screw inside the hose nipple) but needed to be cut to place it in our type of distributor so no many options kept over.I think you can only try this in a distributor machine as my neighbours aren't so pleased with acceleration tests and my back isn't pleased with in and out that car...

3) kept ofcoarse the heavy duty break points.

It was fun and not expensive , so a i'm a experience richer.