Large RPM and Vacuum drop when shifting from park to gear

[AJ/FormS]

Well, unless you can't suck very hard ,lol.
Don't laugh, using lung-power alone, I doubt you can get anything started.
There is a technique;
You put the line between your teeth and suck, then capture the vacuum in the line by biting down,repeating as often as it takes that the rpm no longer rises. Then, still biting down, if you have a lite, read your timing. Then relax your bite and read again. If your diaphragm is not leaking, you will get a difference. If your diaphragm is perforated, you will not get any vacuum built up, and so, no timing difference..
I Tee a vacuum gauge into the line and can read the progress. It takes a good technique and a lotta lung power to hit 15 or so.

 

[yellow rose]

Well, unless you can't suck very hard ,lol.
Don't laugh, using lung-power alone, I doubt you can get anything started.
There is a technique;
You put the line between your teeth and suck, then capture the vacuum in the line by biting down,repeating as often as it takes that the rpm no longer rises. Then, still biting down, if you have a lite, read your timing. Then relax your bite and read again. If your diaphragm is not leaking, you will get a difference. If your diaphragm is perforated, you will not get any vacuum built up, and so, no timing difference..
I Tee a vacuum gauge into the line and can read the progress. It takes a good technique and a lotta lung power to hit 15 or so.

LOL...I have a machine to do that for me!!

 

[DrCharles]

I use my tongue to block off the hose in between sucks. Yes, I know how that sounds.

I'd like a vacuum can that is fully advanced at 8" Hg. since that is all my engine can muster at 1200 rpm idle. I think FBO (Don) can make one, but I don't think there is an off-the-shelf unit that will fit my Mopar distributor.
As it is, I run 16 initial, 27 at idle, long slow centrifugal advance thereafter, plus a vac can that starts advancing at 10" or so. Cruise is 14-15" which is full advance.

 

[gregcon]

Sucking won't tell you a lot. The average person can only suck an inch or two of vacuum. I could make a lot of dirty jokes at this juncture, but that's something anyone could do.

Try blowing into the cannister....if it leaks, it's bad. If it doesn't, it's probably good. The next step would be to apply vacuum from a good source to see if it causes the arm to move in.

 

[Dana67Dart]

As others have said, apply a vacuum to the hose going to the can.

I use a vacuum hand pump. With the timming light you can watch the advance happen. You can also hold the vacuum and if the timming stays, the can is not leaking.

To other poster, there are adjustable cans, some have a screw to adjust the max advance some have springs and stops that can be adjusted to achieve the curve of your choice.

 

[Mopar Sam]

Lets make this simple, just temporarily hook it up to manifold vacuum and see if the timing changes. No need to suck on a hose unless the other end is in your favorite beverage.

 

[TT5.9mag]

Ported vacuum has no purpose other than emissions

Fuel mileage

 

[TT5.9mag]

You can do everything inside the distributor that hooking the vcan to manifold vacuum will do. You cannot do everything inside the distributor that hooking the vcan to ported will do. For a street car the vcan should be on the sparkport and you should build your curve with springs. @Mattax has good info about springs with long loops and specific curves that will bring in idle timing after initial.

 

[Mopar Sam]

You can do everything inside the distributor that hooking the vcan to manifold vacuum will do. You cannot do everything inside the distributor that hooking the vcan to ported will do. For a street car the vcan should be on the sparkport and you should build your curve with springs. @Mattax has good info about springs with long loops and specific curves that will bring in idle timing after initial.

If you are referring to my post, I said hook it up to manifold temporarily.
Just to test if the v can was working.

 

[gregcon]

Ported vac advance has no effect on mileage, at least not mileage at any sort of mph where mileage is measured

 

[TT5.9mag]

Mopar Sam I knew what you were saying. The post was not directed at you. It was information only and a response to gregcon.

Ported vac advance has no effect on mileage, at least not mileage at any sort of mph where mileage is measured

This is just simply not true.

 

[Mattax]

And emmisions have nothing to do with using ported or manifold vacuum.
You can look at the pre-emissions cars and the shop manuals to see that for yourselves.

 

[AJ/FormS]

Ported vac advance has no effect on mileage, at least not mileage at any sort of mph where mileage is measured

As opposed to what?
With a [email protected] cam, my combo got best fuel mileage at ~56* @85mph=1900rpm; but I don't always give her what she wants.
With my [email protected] cam, she likes 60* @65=2240
So,
You can't make
a blanket statement like;

Ported vac advance has no effect on mileage

Without a qualifier; As stated, that statement is false.

But if you say;
were the V-can is hooked to, makes no difference,
well them, that could be correct.
__________________________

The fact remains that;
the smaller the cam, and
the higher the cylinder pressure in that small-cam combo,
the less able the engine is do deal with tons of Idle-Timing; due to the butterfly to Transfer slot relationship having to fall into a very small window, before you run into tip-in issues, that call for early pump-shot to drive thru. As soon as the throttles are tipped in, the timing can be ramped up; and that is exactly how the sparkport works.
At idle, your automatic-equipped engine only needs enough power to idle on, and to not stall when put into gear, pretty much any old timing will do that., sometimes even down to 5*Advance.
And manual transmission cars are a special case.

As regards power and driveability, all our timing controls are designed to do one thing, to deliver the maximum amount of energy available in the fuel, to the piston, when it is in the best possible position, to transfer that pressure to the crank; for as many conditions as possible, as regarding load and rpm. This is most critical from stall to about 3600 rpm. After that the burn changes very little.
From stall,down to idle, there is very little advantage to perfection here. Furthermore, too much pressure is harder to drive, so you can tune this area very nicely with timing. It does not have to be super-snappy, because most of the time when you are in this zone, you are either just passing thru to stall-rpm, or cruising, or at Part Throttle. I mean it doesn't have to be lazy, but it also doesn't need to be perfect. And the more timing you have in this zone, that does not drop out with load (read mechanical), the easier it is to hit the detonation wall. This is why I run a 22* Vcan, and just 14 idleTiming, and I adjust the Vcan to to be fully proportional thu-out it's range of applied vacuum; so it's always ready and willing to drop out, and to slowly ramp back in. Cuz that's how I drive; namely, lots of cruising around, interspersed with periods of brisk acceleration, and since I live in the country, it's always a minimum 30 to 40 mile round-trip to go anywhere. So to me, bringing it home, cruse timing is very important.
Oh and since my combo is a manual trans, I am almost never in the zone below where the Vcan is coming in, which, with no load, on my 750DP is about 1600 rpm which is ~12 mph. My mechanical timing does not start until ~1100rpm, which is 8 mph., So below 8 mph, the engine is a nice stable low-powered platform. From 8 to 12 mph, the timing only changes 4*, so while the engine is picking up some power , it is still pretty stable. After 12 mph at PT, the Vcan quickly brings it in so that by 2000, even 1800, the engine is now snappy.Lemmee tel ya, snappy is an understatement; 1800 is 13 mph.
What this laziness does, is ; it allows me to blip the throttle just a bit, and more or less dump the clutch, then drive away like it was an automatic. None of this 1983Mustangchit. Where you had to rev that poor 5.0 to 3000, and slip that clutch for a half a city block, every time you took off. Slight exaggeration but you get the drift.

 

[gregcon]

I said PORTED vacuum advance, not any vacuum advance.

 

[AJ/FormS]

Is English your first language?

 

[gregcon]

Um...yes, it is. Is drunken rambling yours?

 

[Charlie_es_cool]

Hello everyone!

So, it looks like timing is the culprit. Disconnected the vacuum advance line from the manifold and plugged it. The engine ran like crap in park. So, I advanced intial timing by turning the distributor. Idle quality began to improve but....... I cant advance it any further because my advance canister is hitting my intake manifold. How could I solve this?

 

[DrCharles]

Are you sure you have located TDC accurately and can actually check where your timing is? Best idle is likely way too advanced unless you have already shortened the mechanical advance curve in the distributor. Sorry if this has been already covered in the thread ;)

But to answer the question you asked, you could either move all the wires one hole over, and rotate the distributor 45 degrees, and go from there. Or pull the intermediate shaft up, rotate it one tooth, and re-engage the gear.

 

[Charlie_es_cool]

Are you sure you have located TDC accurately and can actually check where your timing is? Best idle is likely way too advanced unless you have already shortened the mechanical advance curve in the distributor. Sorry if this has been already covered in the thread ;)

But to answer the question you asked, you could either move all the wires one hole over, and rotate the distributor 45 degrees, and go from there. Or pull the intermediate shaft up, rotate it one tooth, and re-engage the gear.

I haven't checked if TDC is marked correctly. I don't own a timing light (yet), should have it by monady or tuesday. I really don't know what my distributor curve is, since I bought the car as is and the previous owner also bought it in the state it is now.

To clarify, one of your suggestions is to move the wires on hole over COUNTERCLOCKWISE and rotate the dist 45 deegress CLOCKWISE.

 

[Mattax]

Leave it alone for now. When you get the timing light and a tachometer then you'll know if you need to reclock the wire posititions.

 

[Charlie_es_cool]

So, it turns out my car had wayyyy to much initial timing.

I checked it with the timing light and had 35 degrees of initial timing with the manifold vacuum disconnected!!! So I retarded the timing until around 15 degrees of initial. My car idles at around 1100, and putting it in gear drops it to about 900. I didn't go any lower than this, because I noticed my voltage drops too much if it idles lower (sub 12 volts).

I noticed that at these idle numbers, my timing is not constant. The mark moves between 15 and 20 degrees. My idle is lopey and rpms oscilate +/- 50 rpm. Could this lopey idle be the cause of my "unstable" idle timing? Or could my timing light be defective?

 

[Mattax]

So, it turns out my car had wayyyy to much initial timing.

I checked it with the timing light and had 35 degrees of initial timing with the manifold vacuum disconnected!!!

Good Job!
The shop manual may cover this but allow me to mention it anyway. Most of the time, whether stock or hot rodded, timing is checked with the vacuum advance disconnected and the vacuum source plugged. Golf tees in the hose are favorite plug.

So I retarded the timing until around 15 degrees of initial. My car idles at around 1100, and putting it in gear drops it to about 900. I didn't go any lower than this, because I noticed my voltage drops too much if it idles lower (sub 12 volts).

If possible, start another thread on the voltage issue. Mention how and where you are measuring it and if any non-factory electric items have been added to the car.
In the meantime charge the battery with a charger. On a factory car, it can idle fine on 12 to 12.5 Volts (battery power) for quite awhile. You'll just need to recharge the battery with a charger when done.

I noticed that at these idle numbers, my timing is not constant. The mark moves between 15 and 20 degrees. My idle is lopey and rpms oscilate +/- 50 rpm. Could this lopey idle be the cause of my "unstable" idle timing? Or could my timing light be defective?

Timing light is probably OK.
The timing is moving because the distributor's mechanical advance begins somwhere above normal idle speed. Shop manual or emissions sticker in the engine compartment will have the rpm but 650 to 750 rpm is typical on emissions era engines.

Once you get the battery charged up, you can work on reducing the engine speed and adjusting the timing until its down where it should be.
Since the carb has been changed, I'll assume there is no idle solenoid. Yes?
If so, then try reducing the throttle position using the throttle speed screw, and experiment with as initial timing as low as 10*BTDC around 650 to 700 rpm.
If its a factory distributor it might have been set up with an advance intended for initial as low as 5* BTDC, again around 700 rpm.

 

[Mattax]

The timing is moving because the distributor's mechanical advance begins somwhere above normal idle speed.

Here's an example of the timing changes with rpm due to the mechanical advance.
Initial timing for for this engine/distributor combo was 0*, plus or minus 2.5*

You've measured around 15* at 900 and 20* at 1100 rpm.
Lets put that on the same graph paper so you can see why that would be normal advance for many distributors.

An original Chrysler distributor will have a metal tag on the side.

 

[Mattax]

If you're stuck with 900 rpm idle speed for now, my suggestion then is just try to drop it a couple degrees more.
That would probably get the mechanical timing into the acceptable range. I say that assuming the distributor has an advance something close to what would be expected.

unknown cam,

Just saw this. Generally a cam with more overlap will need more initial timing than factory emissions era.
They might have installed a distributor with a more appropriate curve to go with more initial timing.
Based on the two measurements you've posted so far, its not looking that way.
If that turns out to be the case, then that's something you'll want to address.

 

[Charlie_es_cool]

Here's an example of the timing changes with rpm due to the mechanical advance.
Initial timing for for this engine/distributor combo was 0*, plus or minus 2.5*
View attachment 1715602848

You've measured around 15* at 900 and 20* at 1100 rpm.
Lets put that on the same graph paper so you can see why that would be normal advance for many distributors.
View attachment 1715602849

An original Chrysler distributor will have a metal tag on the side.

these graphs are awesome. And yes, I understand what you say about the distributor and how I'm already seeing mechanical advance at my idle speed.

I'll have another look at it tomorrow, but I think my distributor is an OEM style one. If this is the case, could I correct when my mechanical advance comes in with heavier springs? Or will I need a different ditributor?