Question for all those on manifold vacuum

[msgdsrf]

Also thinking that when you switched to manifold vac you likely didn't adjust your carb and that's why is ran worse. You have to adjust the idle mixture to work with the amount of advance.

[jcd9730]

Okay... So why was the can adding 22 degrees advance at idle before I adjusted it most of the way out? It was at almost 30 degrees intial with vacuum advance included, and ran like a turd

[jcd9730]

So I would need to... decrease idle mixture, I'm guessing? Why is that?

Initial is set to 8 now. Low I know, but any more any it pings at WOT. Heaviest springs from the crane kit are in there. Fuel mix is around 2 3/4 turns out, but it smells rich

[geezer#99]

You know what I'd do. Run your vac can any way you want but install the limiter like in the link I gave you. THat'll likely make it run better.
While it's idling can you turn the mixture screws in all the way? If you can then you're idling on the power circuit and it will smell rich.

[jcd9730]

No, if I turn them all in, it will die right away.

I was under the impression that the limiter like in the link, or any limiter, was only needed if there was pinging under part throttle? Thats why I assumed I didn't need it.

It runs better now than it ever has, and it idles when cold much easier too (I dont have a choke yet)

[geezer#99]

So stop over analizing it!
But if you install a limiter and get your vac pot timing adding only 12-14 degrees then you can add more initial timing. You could bump initial up to 12-14. That extra initial will be felt all the way thru your power output. THen you could turn your idle down and fine tune your mixture screws. They should be only 1 1/2 turns out. You'll save gas, save money, pollute less, your truck will stay in tune longer and the seat of your pants will enjoy the feel of that extra power.

[jcd9730]

Haha ok! I think I will experiment with different vacuum settings and see where I get.

The first thing I was going to do was turn the can in and see how much advance I can get

[msgdsrf]

2 1/2 turns is a lot. 1 - 1 3/4 is usually where you should be at.

You need less gas because your combustion is better.

If your pinging at WOT and not partial then it's not your vacuum advance. What is your total timing? Disconnected vacuum, Initial plus mechanical? Do you know you're not running lean at WOT?

Weights don't change total timing or springs, that's the curve. And again not what your dealing with at WOT unless your at less than say 3000 rpms.

[LONGHAIR]

You are making this harder than it needs to be.....and I think it's the adjustability of the vacuum canister that is doing it.
In the simplest form, the canister should simply be about 2" of vacuum less than your vacuum reading at idle. It does not need to be adjustable, just get the "right" one. Then it should only be able to pull about 15º of advance. You should be able to buy a can that is exactly that......simple.

Seems to me like you are trying to force the adjustable can to do something it is not intended to do.....

[jcd9730]

I know pinging at WOT has nada to do with vacuum advance, and I had set the mixture to 2 1/2 turns to rule out leanness as a cause of pinging. I ended up with 4degrees initial and i think it was 26 total? Heaviest weights too.

???

Only way it would not ping. I am positive my TDC is right, because when I changed the HG I checked it

So I added 10 degrees advance from vacuum to put initial at idle to 14. Is this a good idea? Runs fine, though I didnt drive it much. But importantly, does not ping

[72chevyk10]

initial is different from initial+vac. initial should be somewhere around 8-14~(higher the better to the point of detonation and starting issues. also i dont think id go anything over 20*inital) then vac adds 10-14~ to that. then total should be "all in" somewhere between 32-36* at 2500-3500 (whatever the engine likes better) the 32-36 does NOT include the vac added to that number have fun its a lot of trial and error

[geezer#99]

[QUOTE

So I added 10 degrees advance from vacuum to put initial at idle to 14. Is this a good idea? Runs fine, though I didnt drive it much. But importantly, does not ping[/QUOTE]

Now you're on the right track!
If it starts good with 14* initial run it like that. Fine tune your carb and enjoy!

[67 chevelle]

The vacume advance is very important in saving your starter and makeing it work less at startup , then when the engine fires you get the advance the engine wants

[geezer#99]

Originally Posted by 67 chevelle

The vacume advance is very important in saving your starter and makeing it work less at startup , then when the engine fires you get the advance the engine wants

Could you explain that a bit better!

[67 chevelle]

without a vacuum advance you have to run alot of initial advance , that intern makes the engine hard to turn over as the starter is fighting all that spark advance

[jcd9730]

The starter doesn't fight spark advance. All the starter does is turn the flywheel/flexplate which turns the crankshaft and camshaft, nothing more. The spark comes from the camshaft turning the distributor which causes spark.

Too much vacuum advance can make it hard to run and idle, but has nothing to do with the starter itself

[geezer#99]

He's partly right Josh.
Too much initial will make it hard to start. Your starter won't have enough power to crank it over because your plug is firing the mixture in the chamber way too early. THe burning mixture wants to go the wrong way. Down towards the piston instead of out the exhaust valve.
He's wrong about the relationship between vac and initial. Vac advance isn't even needed. It's just a bonus to advance your timing during low load cruising.
It's the total combo you're after. Initial plus mechanical and vacuum.

[jcd9730]

Oh, yeah thats true. Well, the starter will crank just fine, but it wont 'catch' so it'll just spin

I've tested this, on accident.... Haha

[jcd9730]

Well, vacuum advance wont I mean

[67 chevelle]

The engines I play with are slightly differant , alot of big blocks with high compression , If you have a distributor that has a 20 degree total advance curve , and you want 36 degrees total you need to run 16 initial , that will kill a starter in short order , as its fighting to start the engines spark advance . The same applies to all engines , thats why ford had spark retard on their old hand crank engines .

The more initial spark advance , the harder the engine is to start irregardless of vacuum advance , once its running and pulling vacume the advance comes in for smooth idle and better combustion , fuel economy , exc , with a vacuum advanced distributor , im sure its the major reason they were developed

[geezer#99]

So i guess 36 degrees locked in in your bbc wouldn't start eh!
I've built a bunch. Small and big blocks. One was an L88 with 12.5 to 1 compression, ZL1 640 lift cam, the whole nine yards. Ran 24 initial, 14 in the mechanical and for giggles another 10 from the vac pot. Cranked and fired with no kick back. The trick with it and a motor with 36 degrees locked. Power to the dizzy had a switch in it. Get her spinning, flip the switch and boom she's running.
You don't set your total timing by planning on a set number. You experiment with how much initial your motor will start well with, add whatevers needed in mechanical to acieve 32-36 degrees all in by 3-3600 rpm and then add a bit of vac advance to help with the tuning of your carb and the occasional time you're at a steady cruise.
I ran a sbc with 22 initial, 12 in the dizzy and 12 vac. No switch. Never had a problem with hard starting.
Anywho, apoligies to Josh for taking his thread sideways!

[jcd9730]

No worries, interesting to read!

[msgdsrf]

Originally Posted by jcd9730

I know pinging at WOT has nada to do with vacuum advance, and I had set the mixture to 2 1/2 turns to rule out leanness as a cause of pinging. I ended up with 4degrees initial and i think it was 26 total? Heaviest weights too.

???

Only way it would not ping. I am positive my TDC is right, because when I changed the HG I checked it

So I added 10 degrees advance from vacuum to put initial at idle to 14. Is this a good idea? Runs fine, though I didnt drive it much. But importantly, does not ping

So, you understand mixture screw only effect idle? Your only loading up your spark plugs if anything and won't help WOT predetination.

Initial is set without vacuum adv hooked up so target should look more like 14 initial plus your 22 mechanical for 36 total, then vacuum adds another 10 for cruising. That's very standard.

I wonder when your weights begin to advance, like maybe very soft springs OR your running too small a seondary jet.

[jcd9730]

The weights were the heaviest I had from two advance kits, and the most initial I could do was 4 degrees. I suppose it is possible TDC is off, but I am positive its right on.

As for jets, I've no idea. I have a quadrajet, and I paid a shop to rebuild it. So no clue.