what kills me is that I’ve always been ported vac. This new Holley has practically no vac on that port (very little) so it’s useless as vac advance. And my manifold vac is super strong.
question: wouldn’t I simply adjust dizzy clockwise, slow things down, then manifold vac? I’m sure it’s a stupid question.

 

No, your 14* to 36* of mechanical is good so don't move the distributor again. You need to fix the vacuum advance to get better vacuum advance numbers. Moving the distributor changes the mechanical advance. You can't fix the vacuum advance by changing the mechanical advance.

 

I should know this by now: the first steps we attempted were to get mechanical locked down then we moved to vacuum. Pretty obvious once you say it lol.

NOW, the carb is new and hasn't been tuned at all except my tightening the idle screw slightly to get my idle up to 800 cold. The port vac shouldn't get better or worse by my adjusting the fast idle screw or anything else, so I'm still at a loss on why i was ported before and now am using manifold to get it to change in any noticeable way (very noticeable based on my 22degrees advance) The limiter that was linked seems to be brand specific. although it looks generic, what this is doing is restricting the springs from going out too far (correct me if I'm wrong).

Lastly, when I unplug the manifold vac and before I can plug it when doing all the testing, the hissing sound is extremely noticeable and will shut down the engine if I don't plug it in quickly. thoughts?

 

Exactly! You finally have the mechanical dialed in. Don't change it! And don't mess with it just to fix an unrelated problem.

There are (at least) 5 ways to fix your vacuum advance problem:

1. Lars' instructions include the part numbers for vac advance cans that you may be able to purchase that have the correct 10-12 degrees total for your engine and dist.
2 and 3. Lars' instructions also show his method of limiting the vacuum advance with either a weld, or an adjustable piece that screws to the advance arm.
4. The part @lionelhutz linked to
5. An Accel 31035 can be adjusted to 10 or 12 degrees of vac advance, however it has a limited acceptable vacuum range (works fine for my 80, though).

 

someone should make an easy to adjust can. makes alot more sense considering all the aftermarket changes people do like manifolds, etc. that to me seems to affect timing due to stronger/weaker vacuum. thanks for all the help all. tomorrow i'll fiddle a bit more. it's dark out. thanks again!!

 

You will need to adjust your carb. Does it have a manifold vacuum port, that you can test with your finger and/or a vacuum gauge? You will need a vacuum gauge for the next tuning steps.

Right now, you have a huge hole opened up in the top of the manifold. The "strength" of a vacuum as you perceive it is related to both the area and (differential) pressure. A manifold vacuum port on your carb should have the same negative pressure, but a much smaller opening, so it may not cause a massive vacuum leak that shuts down your engine. The vacuum advance won't know the difference, it cares only about the pressure and will pull 22 degrees advance either way.

Here's my Accel can, internally adjusted to 12 degrees of total advance (most of the other methods limit the travel of the advance lever externally).

 

Ported vac advance was a GM emission control strategy that began around 1966 thru 1980 or so.
Basically retarded the timing about 10 degrees in normal light throttle driving ranges!?!?!?!?!?! WT??

Exhaust ran hot enough to burn up some hydrocarbons.

Cat convertors in 75 without computer control were another not too successful experiment on the populace.

For a performance car SAY NO to RETARDed timing ! LOL

BTW: Just saw this number:


I hope this is not true. It might be. You should confirm tomorrow: (no need to move the distrib)
No vac: Idle is 14 degrees right?
How much rpm does it take to get to 36 advance?
It should be at least 2500 rpm until 36
It should stay at 14 from 600 to say 900-1000 or so. (If not the idle may not be steady) (200 rpm above idle)
Then at say 1500ish you should be half-way there. (20s?)
Then at 2500 you should be at 36. ("all-in" anywhere from 2400 to 3200 is probably fine)

You may still need different springs in the distrib.
"All-in" (36) by 2000 or earlier is too soon.
The factory curve would not be "all-in" til 5000. (too late)

And once you get that right, yes an adjustable vac can purchase is in the works.

It will all be worth it tho, it will run so much better, stronger, cooler, and get better mpg too. Win-win-win. A few more HC emissions maybe.
Hey it's not that much better than a '65 anyway. A new car is 300 times lower. Practically cleans the air as it drives.

 

If you need to reduce the vacuum advance you may as well buy a new one. NAPA Part #: UNI VC1836. This is for a '76 L-82 but will fit. It limits the vacuum advance to 10*.

 

I’m a genius. Let’s limit the vac as we go shall we? The genius part is extremely sarcastic. Ordered the accel but I can get the Napa tomorrow I think

 

I'd just get the NAPA one today that @resdoggie mentioned, and then that will be done.

While you are in there, please take a photo of your weights and springs.

Are you able to map out your advance as a function of RPM? If your mechanical advance doesn't go down until you are below 900 RPM, I'd suspect a broken or missing distributor spring.

 

yes getting it tomorrow. did you see my rig?

 

That's cool for testing. You wouldn't want to run like that bouncing around, though. It might damage your chrome.

 

lol. for testing i swear.

 

when i get the new can we'll see how much changes. i'm going to check the springs carefully regardless. I have a new dizzy coming in as well (99 bucks) to have all bases covered. thank God for amazon and their return policy as well as summit. I think I owe them money at this point. lol.

 

Good news.
Sounds like you are "all-in" at 2000.
A little soon, but not too bad.
I think you have low CR right, so it might like it.
Anyway easy to change later. Just go up on one spring a little stiffer. See how it responds.
I think I am more concerned that the advance starts to come in at 850, very close to your idle.
It might cause your idle to wander/hunt.
I would like to see a little more distrib spring. Advance steady until 200-250 above idle.
After all this work setting up your distributor, why change it? Send the other one back. The $99 ones are no good anyway.
Drop that NAPA vac can in and you are almost ready to drive! Woo-Hoo!

You did a great job getting to this point.

 

Thanks guys. let's see what happens tomorrow/friday. After this hopefully I hold steady without so much advance with the new can. Then I have to adjust the holley. I have my vac gun ready to start tuning that.
Tonight at the vette meet I help organize I brought hotdogs for the crowd. Had to come in my wife's mini van to bring the bbq grill lol. miami every wednesday. I'm the idiot with the cigar cooking the hot dogs. the balding one. lol

 

got the napa can and the new dizzy. if the springs are an issue i'm dropping this one in. if not adding the can instead. i'll be on this today God willing.

 

to map the advance/rpm and do anything else I need to rev up. the new neighbors have a new baby girl. And where is her window? the closest one to my vette. They've never complained (young couple helping them fix their yard etc) but I know it must be annoying. Will wait to continue tomorrow after 10am.
springs seem ok. I forgot to take a pic and came inside to take a bath. Tomorrow I'll shoot pics.

1) install vacuum can and try the vac advance again to see how far advanced i'm at.
2) if we're on the money then I'll stop fooling around. We time it at 10-12 out (10 I assume due to the can I bought) then tune the idle screws on the holley.
3) What has me worried is that under load when I punch it I DO NOT hear/feel the secondaries open at all. This is before I readjusted for timing when I drove to a friends house. I know I have to tune. The worst part is according to the manual the secondary adj. screw is underneath!! So I'd have to remove carb to work on that and put it back. What a horrible design flaw IMO.

Anyway tomorrow it is.

 

It's a vac secondary Holley.
You should not "feel" the secondaries open, if you do what you feel is a "bog".
You may "hear" them though. They should open somewhere around 3500 & up on WOT. Gradually. Gradually increasing "roar". If it bogs you need a stiffer spring. The likelihood of a softer spring giving you more than 1-2 HP is slim. But to really tune that means a lot of spring changes. You go lighter until it bogs, then you go stiffer again until the bog goes away. Can be done with timed acceleration runs also, But that should be last on your list. (Call it step #4)

It's a completely different feel than a double pumper.
If it pulls hard to 5500+ leave it alone. It's new it's probably OK. If the sec are not opening at all it will probably barely rev past 4000.

More than likely you could fine-tune the main jetting if you want. Later. Spark plug color, A/F ratio etc. etc. (Call it step #3)

Idle mixture tuning is most likely enough for a "driver" Tune that for lean drop off (-50 rpm) plus 1/4 turn, and check/tune it for highest idle vac (at same rpm). They should be very close but higher idle vac would win. Ideally you want it within 1/16 turn +/- . Idle mixture tuning also affects your cruising smoothness and MPG. Do this as soon as you have the timing settled. (That's step #2.)

But the distributor/timing curve tune has far more performance detriment when it is off.
That's why you tune the timing first. (Step #1)

 

replaced dizzy with new napa can to see if any difference existed. with vac connected after all steps 51 degrees at 3500 rpm's. i'm assuming 15 degrees (51-36). let me check in a minute properly. this is after mech advance done.