Motorcraft 2150 Spark Port

[TenSeven]

The 'Spark Port' on my 2150 carb used for distributor vacuum advance has an opening but no nipple connection and when I connect a hose into it no 'obvious' air can be passed thru or sucked out. Is that normal with the engine off? Did there used to be a metal nipple pressed into that opening?

https://goo.gl/photos/8tfoBUGGGybxqAGy5

Also, since I've switch over to a manual choke, if the spark port is blocked, can I just use the choke pull down vacuum port for the distributor vacuum advance?

 

[jeremysdad]

Yes to the nipple. http://grantorinosport.org/BubbaF250/carb/carb20.html

You'll get mixed answers as to using full manifold vacuum, but...yes, but mileage and emissions will suffer. Bit more power though. In theory.

 

[TenSeven]

Yes to the nipple. http://grantorinosport.org/BubbaF250/carb/carb20.html

You'll get mixed answers as to using full manifold vacuum, but...yes, but mileage and emissions will suffer. Bit more power though. In theory.

Thanks jd.

I could probably jam a nipple connector in there and use it, but is there a reason I can't get air in/out of it?

 

[RonD]

Use manifold vacuum.

But seal that port in the carb.

Carb vacuum, above throttle plate, allows engine to warm up faster and engine will have lower emissions, but it will also have less power.

Here is a C&P I did from another thread.


This is a long discussed topic, vacuum advance and intake or ported, lol.

There actually is a correct answer but it is engine specific, and a few variables are involved.

It is often said ported vacuum was used for lower emissions, which is partly true.
Car makers used lower compression engines which have bad emissions cold, so ported vacuum was used to warm them up faster.

First, all distributors(in this example) have centrifugal advance, weights and springs.
This advances spark timing based on RPM.

Why do we even need to change spark timing?
An air/fuel mix has a burn rate, from the time it is ignited until it reaches explosive force.
The burn rate for the most part is a fixed amount of time, based on the mixture, i.e. 14.7:1.
You want the explosive force part to happen at about 15deg After TDC, on most engines, this gives the piston the best leverage on the crank, earlier is less power later is less power, before TDC is minus power .

Because the burn rate time is fix but the RPMs are not, the faster the piston is moving the more advanced you want the spark so fuel mix has time to burn then explode after TDC.
At red-line RPM say 6,000 the spark advance might be 36deg on centrifugal advance.

So why vacuum advance?
Air/Fuel mix is why
Idle and cruising air/fuel mix is "lean", not pinging/knocking lean but not Rich.
So the burn rate is the same, just the RPMs are different which centrifugal advance takes care of.

When you step on the gas the air/fuel mix gets Rich, 13:1, instantly, and a Rich air/fuel mix has a shorter burn rate, so if burn rate changes spark advance needs to change, so vacuum advance was added.
Intake vacuum is highest at idle and cruising so it holds advance for the slower burning Leaner mix.
When you open the throttle fuel mix gets richer and vacuum drops, vacuum advance is reduced for the faster burning mix.

Ported vacuum, with lower compression engines you need them to heat up faster and stay warmer to lower emissions.
With less vacuum advance the slower burning mix explodes closer to TDC, less power but more heat is generated.

Many car makers used both, ported when engine was cold and then intake vacuum when engine was warned up.

Both have their points for economy and performance, correct choice is engine and driver based

 

[jeremysdad]

Wrong hole or carb from a vehicle with no need for vacuum advance port? Idk...could be plugged with carbon or other gunk. Dirt dauber? Jerks love my extra hose collection.

 

[TenSeven]

Wrong hole or carb from a vehicle with no need for vacuum advance port? Idk...could be plugged with carbon or other gunk. Dirt dauber? Jerks love my extra hose collection.

Thanks jd.

 

[TenSeven]

Use manifold vacuum.

But seal that port in the carb.

Carb vacuum, above throttle plate, allows engine to warm up faster and engine will have lower emissions, but it will also have less power.

Here is a C&P I did from another thread.


This is a long discussed topic, vacuum advance and intake or ported, lol.

There actually is a correct answer but it is engine specific, and a few variables are involved.

It is often said ported vacuum was used for lower emissions, which is partly true.
Car makers used lower compression engines which have bad emissions cold, so ported vacuum was used to warm them up faster.

First, all distributors(in this example) have centrifugal advance, weights and springs.
This advances spark timing based on RPM.

Why do we even need to change spark timing?
An air/fuel mix has a burn rate, from the time it is ignited until it reaches explosive force.
The burn rate for the most part is a fixed amount of time, based on the mixture, i.e. 14.7:1.
You want the explosive force part to happen at about 15deg After TDC, on most engines, this gives the piston the best leverage on the crank, earlier is less power later is less power, before TDC is minus power .

Because the burn rate time is fix but the RPMs are not, the faster the piston is moving the more advanced you want the spark so fuel mix has time to burn then explode after TDC.
At red-line RPM say 6,000 the spark advance might be 36deg on centrifugal advance.

So why vacuum advance?
Air/Fuel mix is why
Idle and cruising air/fuel mix is "lean", not pinging/knocking lean but not Rich.
So the burn rate is the same, just the RPMs are different which centrifugal advance takes care of.

When you step on the gas the air/fuel mix gets Rich, 13:1, instantly, and a Rich air/fuel mix has a shorter burn rate, so if burn rate changes spark advance needs to change, so vacuum advance was added.
Intake vacuum is highest at idle and cruising so it holds advance for the slower burning Leaner mix.
When you open the throttle fuel mix gets richer and vacuum drops, vacuum advance is reduced for the faster burning mix.

Ported vacuum, with lower compression engines you need them to heat up faster and stay warmer to lower emissions.
With less vacuum advance the slower burning mix explodes closer to TDC, less power but more heat is generated.

Many car makers used both, ported when engine was cold and then intake vacuum when engine was warned up.

Both have their points for economy and performance, correct choice is engine and driver based

Geez, awesome right-up Ron.

Now that I've installed a manual choke, is there any reason I can't disconnect the choke pull down diaphragm and use that vacuum port for the distributor vacuum advance?

 

[RonD]

You can but it is a "Ported" vacuum source like the "spark port"

Ported vacuum sources are between throttle plate and air cleaner, on carb or fuel injected engine, it has low vacuum when throttle is closed, engine idling, as throttle opens more air flows in past the port's opening in the carb so vacuum suction increases.
In this case the choke plate would be pulled open more and more as vacuum increased allowing more air to flow into the engine, so engine's Rich fuel mix from closed choke could lean out for higher RPM driving.
Then choke plate would close again as RPMs dropped, ported vacuum drops, so richer mix would come back because it is still needed by cold engine at lower RPMs.

As said above Ported vacuum is good for faster engine warm up, but unless you only drive vehicle on 10 minute trips a regular manifold vacuum for distributor will give you better performance and MPG.
Regular manifold vacuum is found between throttle plate and intake valves

 

[TenSeven]

Interesting stuff, you are a wealth of information Sir, thanks.

 

[TenSeven]

Is the port on the back of the carb that the PCV hose is connected to considered ported or manifold?

 

[RonD]

Manifold.

Below throttle plate is manifold
Above throttle plate is Ported

PCV and Power brake booster use manifold vacuum.

And there can be a base plate, spacer, for EGR valve use, or manifold vacuum

 

[TenSeven]

Thanks buddy.