[Carmine]

The heads are "D" port because I bought the after market RA/HO exhaust manifolds for them.
There is no one better source of vacuum, then the next. I checked every port/source on the carb. and intake manifold. No matter where I checked, it was always about 10 inches. I'll recheck all sources for a better vacuum advance, but as I mentioned, no significant changes between them. I looked in my repair manual which states that timing should be at 12 degrees BTDC. I'm at 8 degrees. It also said my stock CR should be 8.2. I'm not sure what it is. I believe I will slowly advance the timing to at least 12 degrees and see how the engine reacts. I'll then check the vacuum. What I'm looking to attempt , is have all the vacuum lines hooked up properly. Have the timing and carb. adjusted properly and hopefully this will give me enough vacuum to operate the PB safely. That is my goal. I want the PB working. Whether it be a cam change during next winter, or a vacuum pump for now, I'm determined that they work properly before leaving my garage. I just wish the PO left things alone. I don't think he knew what he was doing. He knew even less then me which isn't much to begin with. He butchered a lot of things. Some times I have regrets about buying this car and wish I would have just walked away. Oh well. It's mine now, Carmine.

[Carmine]

Originally Posted by geeteeohguy

What year and what engine?

1971 numbers matching 400 engine.

[Squidward]

Do you have a dial back timing light, or regular? If regular, you can make marks with a sharpie on your balancer. Assuming a stock-ish 6.8" diameter, 1" = 16.8 degrees. If your diameter is different, just use 360 / (pi*diameter) to give you degrees per inch. Make a mark at 1" and 2" to the right of the tdc line. When the 1" mark aligns with zero, you are at 16.8 degrees BTDC, and so on. Or, get a timing tape.

Set your initial at 12-14 (vac advance disconnected and plugged). Now plug in your vac advance to a manifold source. If your idle speed increases to over 800 rpm, then adjust your idle speed screw so that it brings idle speed back down to 800 rpm. Now connect a vacuum gauge to a manifold vacuum source (may require use of a vacuum tee and some hose) and see what your vacuum reading is. I'll bet it is now more than 10". And take a look at your timing now to see how much the vacuum advance added. If you started at 14 init, and then plugged in vac advance and timing is at 29, then your vac advance is adding 15 degrees.

Next step would be to tune your idle mix screws in equal small (1/4 to 1/2 turn) increments to achieve max vacuum, while maintaining idle speed at <800 rpm via the idle speed screw.

Report back how it runs with new timing, and how vacuum changed. This should get you in the ballpark.
This should get you close.

[Joe's Garage]

I agree with Squidward - you need a lot more timing.

This is a little long-winded and slightly off-topic, but still a cheap, easy way to check your total timing. I think a bunch more initial timing will really make a difference both in your power brakes and in your overall performance.

To 'POWER TIME' your Pontiac V8:

Cut a 2 1/8" piece of tape (I use 1/2" wide, white pin-striping tape).

Clean the balancer really well, for a couple inches, measuring CLOCKwise from the timing mark. Brake cleaner or acetone-type clean.

Apply the tape, starting at the timing mark and going CLOCKwise. You could even just use a sharpie to make another timing mark at the 2 1/8" clockwise point.

Disconnect the vacuum advance line and plug the vacuum source.

Start the engine and check the timing, with the vacuum advance disconnected. The '0' TDC mark will be somewhere in the middle of the tape you just applied, and the trailing edge of the tape will be aligned with whichever setting you have your timing set to right now.

To get total mechanical timing set close to where the stock Pontiac engine will run best, briefly rev the engine up to about 3k - 4k RPMs and adjust the distributor until the '0' timing mark on the timing cover lines up with the leading end of the timing tape (the end NOT lined up with the timing mark on the balancer). It will take multiple adjustments to get this correct.

Note that this step is MUCH easier with a helper inside the car to run the revs up by momentarily pushing on the gas pedal while you adjust the distributor.

When you get the '0' TDC mark on the timing cover lined up with the leading end of the timing tape, your total timing will be ~36 degrees - great for most stock-ish Pontiac V8s.

With the engine idling, you will find that your initial timing is around 15-18 degrees BTDC. So long as it still starts well when hot, and does not 'ping', you will also find that throttle response is much better now.

Adjust lower as needed, usually about 2 degrees at a time.

And, as Squidward pointed out, you will need to adjust your idle speed down and re-adjust your mixture screws. Particularly if you use manifold vacuum for your vacuum advance.

If you would rather just see how more initial timing will affect your manifold vacuum, disconnect the vacuum advance and plug the vacuum source and set your timing up to AT LEAST 15 degrees BTDC.

EVERY stock, low-compression Pontiac V8 I've worked on ran MUCH better with at minimum of 15 degrees of initial timing. Some liked ported-source vacuum advance and some liked manifold-source vacuum advance.

Your manifold vacuum readings should come up 6 inches (probably more). That alone might fix the power brake issue.

Good luck!

[Greg Reid]

Originally Posted by Carmine

First pulled off the vacuum advance line on the distributor and held my finger over the hose. I could feel a little sensation of a vacuum pull. Even when the line was off, it didn't change the idle of the engine which was at about 850 rpm's. Hmmmm..................Not sure what that means.

I think you guys may not have noticed this? I think you need to first verify that some amount of vacuum will advance the distributor...even if you have to connect a hose to it and suck while watching the advance plate on the distributor.

[Squidward]

Originally Posted by Greg Reid

I think you guys may not have noticed this?

I think it's best to get a good baseline with the timing, and then go attack the idle mix. Then you can tweak the idle mix/idle speed screw to find out how responsive your mix screws are. At that point you can see if they adjust too far out or in to get the best vacuum reading.

[STEELCITYFIREBIRD]

I typed a long reply yesterday, and I guess I never hit submit.

It has all been covered, and as Greg pointed, out I wonder if you have 10" @ port where VA is hooked up now also. And if VA is operational.

Are you having issue with the power brakes now or are assuming/expecting to?

Do you have adjustable valve train?

Some dizzy and perhaps carb mods might be needed with the advanced timing.

[Greg Reid]

@ Squidward, Yeah, I understand that but I'm wondering why it makes no difference if the vac advance is hooked up or not. Is 10" too little to move your average distributor advance?
Most advise to make his adjustments with the vac advance plugged, correctly so, but it appears that in his case, it makes no difference. I'd be wondering about that myself.

[Formulajones]

Originally Posted by Greg Reid

@ Squidward, Yeah, I understand that but I'm wondering why it makes no difference if the vac advance is hooked up or not. Is 10" too little to move your average distributor advance? .

Sometimes. Depends on the can he has. I'd need some numbers off of it to verify. Some cans aren't that sensitive and others more so. If it's an aftermarket can with an adjustable vacuum screw, it could be cranked tight to the point that 10 inches does nothing for it.

Without being there and seeing it I can't say for sure. A hand held vacuum pump is a great thing to have in this situation, you can slowly pump the advance and see exactly how much vacuum is needed to start moving the breaker plate, and how much vacuum is needed to reach it's full movement.

Or it could be as simple as the diaphragm leaks and the vacuum advance is just inoperable. The hand held vacuum pump would answer this question too.

[Greg Reid]

Originally Posted by Formulajones

Sometimes. Depends on the can he has. I'd need some numbers off of it to verify. Some cans aren't that sensitive and others more so. If it's an aftermarket can with an adjustable vacuum screw, it could be cranked tight to the point that 10 inches does nothing for it.

Without being there and seeing it I can't say for sure. A hand held vacuum pump is a great thing to have in this situation, you can slowly pump the advance and see exactly how much vacuum is needed to start moving the breaker plate, and how much vacuum is needed to reach it's full movement.

Or it could be as simple as the diaphragm leaks and the vacuum advance is just inoperable. The hand held vacuum pump would answer this question too.

Yes, exactly what I'm driving at..He may have an adjustable can and not know it or a bad diaphragm and not know it. Not saying that would rectify all of his problems but that is one thing that needs to get sorted and it's an obvious issue to look at.

[Formulajones]

Yeah I think we are all on the same page and want to help the guy. It's just hard to do from the internet.

I do agree with others as well. I'd like to see a little more initial timing, that will help the vacuum reading. But it will probably take some work in the breaker plate slot to limit total advance to get things where they need to be so his solution is probably going to take some work in different areas of the distributor.

[74Grandville]

Originally Posted by Formulajones

Sometimes. Depends on the can he has. I'd need some numbers off of it to verify. Some cans aren't that sensitive and others more so.

agree. if you have low vacuum, you need a can that can support that scenario.

maybe buy a replacement that is ment for a RAIV, i don't have a number off the top of my head, but the RAIV was 11inch stock and that is with a bunch of timing at idle.

[Carmine]

Everyone is putting a lot of time and effort in writing these threads and trying to help me. I sincerely appreciate it and am grateful. Some I understand. Other stuff is a little foreign to me, but that's ok. I was up early this morning and out to the garage. I checked the timing-8 degrees advance and vacuum-10 inches. Nothing changed from yesterday. I unhooked and plugged the line from the intake port that feeds the distributor vacuum advance. (Did this before checking the timing). Motor was previously warmed up and idling at about 800 rpm's. I advanced the timing to about 12-13 degrees. Motor idle increased and smoothed out some. I then checked the vacuum which was at 12 inches; maybe it would bounce to 13 inches. Brought the idle back down to 800 rpm's. Hooked up all the vacuum lines and the idle increased some. Brought it back to 800 rpm's. Checked the timing and it was at about 16 degrees. I also checked the port on the rear of the carb. fitting that is shared with the PB and the heater vacuum. This still registered 12-13 inches. I tried adjusting the carb. using my vacuum gauge. I gained some increased vacuum but nothing to really brag about. I'm not troubled by increasing the initial timing even more if that would be a good idea. I don't anticipate pinging. I probably have a low compression engine and I always put 93 octane in all my vehicles. I also add a bottle of Lucas Octane Booster to every tankful. I think it works. I haven't left the garage with the car yet, but the brake pedal does feel somewhat better. Is it enough; not sure but I think not. Think I'll work on bleeding the lines next. Just a quick question. Did anyone ever use a vacuum gauge to adjust the timing?? I'm told that you turn the distributor to get the highest vacuum reading, then back it off 2 inches. Does that sound feasible?? Many thanks to all, Carmine.

[Formulajones]

12-13 inches is plenty to run the power brakes so you made good progress.

The vacuum and initial timing setting is an old school way of doing it.

14-16 degrees of initial timing is not out of the ordinary on an engine with tight LSA and cams that have some overlap. Without knowing what you have for sure it's hard to suggest a definite setting so I would suggest setting it where drivability is best, and creep up on it. 12 degrees you have now is a pretty common place and by no means is it too much. From your description you are heading in the right direction, and it sounds like your vacuum advance is now starting to respond. Maybe put some miles on it like that and see how it acts before making any big swings at it. Without knowing total timing I'm reluctant to suggest you go much further with your initial setting.

[Squidward]

In my experience you will begin to have hard starting at initial timing of 18+. I run at 16 normally, but put it out to 18 in colder months for track time only. In the summer months 18 is right where I might expect some cranking issues.

It is surprising that you only got a couple of degrees out of the vacuum advance. It might be bad, or a stock unit that requires a little more suck to give full advance. Pics of vacuum advance? Stock or aftermarket? I like the adjustable units with the limiter.

Unless you have a freaky cam, I think you could get 15-17" out of it.

Concerning your vacuum connections: I tee my vac advance with the tranny vac modulator off a full time ("manifold vacuum") port on the carb, and I run the power booster off a nipple on an intake runner. Pcv gets its own "fat" nipple on the carb.

[TedRamAirII]

Your brake pedal may feel better when driving, as deceleration will raise your vacuum level.

[Carmine]

Originally Posted by Squidward

In my experience you will begin to have hard starting at initial timing of 18+. I run at 16 normally, but put it out to 18 in colder months for track time only. In the summer months 18 is right where I might expect some cranking issues.

It is surprising that you only got a couple of degrees out of the vacuum advance. It might be bad, or a stock unit that requires a little more suck to give full advance. Pics of vacuum advance? Stock or aftermarket? I like the adjustable units with the limiter.

Unless you have a freaky cam, I think you could get 15-17" out of it.

Concerning your vacuum connections: I tee my vac advance with the tranny vac modulator off a full time ("manifold vacuum") port on the carb, and I run the power booster off a nipple on an intake runner. Pcv gets its own "fat" nipple on the carb.

I know the HEI is a Delco Remy brand. I'm not sure about the vacuum advance. I can get some pics tomorrow of it and post them. What is an "adjustable can" that I see mentioned in a few threads?? Would this also be known as the vacuum advance that is attached to the distributor?? It seems that no matter what port or source I test, the results don't really vary. Whether the carb. or intake, the inches stay pretty much the same. Thanks, Carmine.

[Carmine]

Originally Posted by Formulajones

12-13 inches is plenty to run the power brakes so you made good progress.

The vacuum and initial timing setting is an old school way of doing it.

14-16 degrees of initial timing is not out of the ordinary on an engine with tight LSA and cams that have some overlap. Without knowing what you have for sure it's hard to suggest a definite setting so I would suggest setting it where drivability is best, and creep up on it. 12 degrees you have now is a pretty common place and by no means is it too much. From your description you are heading in the right direction, and it sounds like your vacuum advance is now starting to respond. Maybe put some miles on it like that and see how it acts before making any big swings at it. Without knowing total timing I'm reluctant to suggest you go much further with your initial setting.

Wish I had more info to offer, but I don't. I share what I can and know. The car came to me this way, without any numbers or knowing anything. When I first drove this car, I went down a slight hill, applied the brake which went almost to the floor before grabbing. Obviously, I didn't go far. I returned and asked the owner if he knew he had a brake problem. Yup. I know. I drive it like that. Are you kidding me?? If I was smart, which apparently I'm not, I should have walked away then. I agree with you, that I will leave the timing as is for now. It is an improvement and I will put a few miles on it before making any further changes. Thank you for your response, Carmine.

[Greg Reid]

The adjustable cans look pretty much like a stock can but they are designed so that with an allen wrench inserted into the hose nipple you can adjust a screw that changes the amount of advance. Pretty handy actually and I think you can buy them seperately from places like Jegs or Summit. I have a couple of aftermarket HEI distributors that come already fitted with the adjustable cans.

[Carmine]

Originally Posted by Greg Reid

The adjustable cans look pretty much like a stock can but they are designed so that with an allen wrench inserted into the hose nipple you can adjust a screw that changes the amount of advance. Pretty handy actually and I think you can buy them seperately from places like Jegs or Summit. I have a couple of aftermarket HEI distributors that come already fitted with the adjustable cans.

OK. Thanks, Carmine.