All Small Six A vacuum advance question-modifying the Autolite 1100 to provide port vacuum and bypass the SCV

[Kritas]

This is my first time dealing with an Autolite 1100 and the spark advance system on an old Ford, so bear with me. I've replaced my stock distributor with an HEI unit. When I made the change, I plugged the vacuum advance port on the carburetor and spliced the vacuum advance unit on the HEI to the PCV line using a 3-way barbed fitting. Since I've been doing some additional work before putting the car on the road, it's only been started a few times since these changes were made and seems to run fine.

My understanding from another thread was that the spark advance on the Autolite shouldn't be used with the new distributor. I want to verify that is accurate and ask if there is a better alternative for providing vacuum to the distributor as an alternative to the PCV line. The carb spacer that I'm using has one port and I'm using that for the PCV line. I could drill a second hole and install a fitting for the vacuum advance to the distributor if required.

 

[bubba22349]

Hi Kritas, you can't use the old SCV Carb as a ported Vacuum source to operate your newer HEI or a DuraSpark II Distributors Vacuum Advance Canister unless you mod it. This is because the SCV Carbs use a combo mixture of Ventra Vacuum and Manifold Vacuum this is based on the engine Load. On the Autolite 1100 Carbs there is a simple way to convert it over to ported Vacuum for use with your Distributors Vacuum Advance this is the Drop A Load Mod if you want to learn how here is the link. https://fordsix.com/threads/delete-scv-on-1100-autolite-for-ported-vacuum.76821/
The other way to do it is to hook the Distributors Vacuum Advance Canister direct to a manifold Vacuum source that is below the Carb on the intake and then plug off the old SCV Carb port. It also a bad Idea to be tapping into the PCV Vacuum Line with a T fitting. Good luck

 

[Kritas]

Thanks Bubba. I figured that might be an issue. I think the simplest thing may be to drill and tap the spacer, but I'll have a look at the link when I get home.

 

[Frank]

Thanks Bubba. I figured that might be an issue. I think the simplest thing may be to drill and tap the spacer, but I'll have a look at the link when I get home.

Yes, if you're ok with manifold vacuum keeping the timing way up at idle and deceleration. I'm not a fan, especially on the Ford 6. Ported vacuum is better in this regard. But the carb mods aren't a quicky fix, so if it idles ok to your liking with M vacuum advance, it's definitely easier. Excessive advance @ no-load idle can cause an intermittent miss, sounds bad.

 

[Kritas]

Well, damn. Given that I may go to FI, I was hoping not to have to do much carb work. Ah well.

 

[bubba22349]

Thanks Bubba. I figured that might be an issue. I think the simplest thing may be to drill and tap the spacer, but I'll have a look at the link when I get home.

No need to Drill and Tap anything you have a good Manifold Vacuum Source all ready Tapped on your Head. See the 90 Degree Fitting and Line just below your Carb Base Mounting in your posted Picture here. https://fordsix.com/threads/firing-order-reversed.84345/page-2#post-677805
All you need is the correct easy to find NPT (Pipe Thread) Vacuum T Fitting and other fittings available at most Automotive Parts stores and many Hardware stores to install it right there in that threaded boss. Edited

 

[Kritas]

Thanks again Bubba. That's a great idea, and I know the fitting you're talking about. I might have the parts to fit that out correctly but will have to check.

 

[Kritas]

Looking at that mod, it doesn't look too bad either. I have a drill press, so doing that isn't a problem. It's easier to just use the existing port I think.

 

[bubba22349]

Yes the Mod is easy to do for a ported Vacuum on those Autolite 1100's .

 

[jamyers]

I wouldn't use the pcv line as a vacuum source, but anything tapped into below the throttle plate will work fine.

Regarding the old ported vs manifold vacuum question, MANIFOLD is the way to go. As per a conversation I had years ago with one of the GM ignition engineers, the ONLY reason they used ported vacuum was to get higher temps at idle for emissions. If you've got an intermittent miss at idle, unless you've got an insane amount of advance, it's not because of ignition - more likely too lean a mixture.

I'd also recomend sticking with the carb - if you think carbs are work, wait until you get knee-deep into the efi swamp, lol.

 

[Frank]

I wouldn't use the pcv line as a vacuum source, but anything tapped into below the throttle plate will work fine.

Regarding the old ported vs manifold vacuum question, MANIFOLD is the way to go. As per a conversation I had years ago with one of the GM ignition engineers, the ONLY reason they used ported vacuum was to get higher temps at idle for emissions. If you've got an intermittent miss at idle, unless you've got an insane amount of advance, it's not because of ignition - more likely too lean a mixture.

I'd also recomend sticking with the carb - if you think carbs are work, wait until you get knee-deep into the efi swamp, lol.

I respect your response. Every engine I've had had ported vacuum, 1960- 1977 including a current daily commuter, a 1959 Rambler. "Emissions" was not yet in the dictionary. Just FYI.

 

[Kritas]

Looks like the Manifold Boys are going to rumble with the Ported Gang.

 

[Frank]

Looks like the Manifold Boys are going to rumble with the Ported Gang.

No sir. I'll take nothing personally. Simply stating that I have never seen a manifold vacuum advance from the factory, so mystified when I hear that ported was an emissions afterthought- it just ain't so. .
Peace.

 

[Kritas]

No sir. I'll take nothing personally. Simply stating that I have never seen a manifold vacuum advance from the factory, so mystified when I hear that ported was an emissions afterthought- it just ain't so. .
Peace.

I'm kidding. The discussion has been very helpful.

 

[Kritas]

Now I'm reading up on ported vs manifold vacuum. Really fascinating.

 

[bubba22349]

Personally I always run a Ported Vacuum to the Distributor Advance most especially on an Auto Trans Street Car. Ford ran a Ported Vacuum on the V8 engine's starting back in 1957 and the Load O Matic systems before that in the about 1949, which was long before emission systems were used. I have tuned engines to work either way Ported or Manifold so you should use whatever works the best for you.

 

[Kritas]

Personally I always run a Ported Vacuum to the Distributor Advance most especially on an Auto Trans Street Car. Ford ran a Ported Vacuum on the V8 engine's starting back in 1957 and the Load O Matic systems before that in the about 1949, which was long before emission systems were used. I have tuned engines to work either way Ported or Manifold so you should use whatever works the best for you.

I've noticed that the timing is up at idle using ported vacuum as Frank pointed out. After doing some reading, it does seem like ported is the way to go for this application since it's for a streetable, non HiPo application with an auto trans. The carb mod for the Autolite seems pretty straightforward to do and I'd only need some set screws (or JB Weld) to plug the holes.



Relax.... I'm kidding.

 

[Kritas]

Edited.... removed for now.

 

[Frank]

JB Weld is great stuff. .
Ported IS manifold vacuum, blocked by the throttle plate at base idle. Manifold advance and ported advance are identical, except at base idle, and the first few * of throttle opening. Idle quality is more controllable with ported. With an automatic trans, there is less rpm drop when engaging the trans with ported.
Sharp off-idle response is accentuated with ported vacuum: When taking off from a stop, manifold vacuum results in a retarding of the timing as load is applied. Ported vacuum spikes the timing ahead, simultaneous with throttle opening.
Highly advanced idle timing is more susceptible to rpm drop with load, the throttle is more closed. If you like any sort of engine tone at idle, requires ported. Timing advanced to the limit at idle (or no load), there is little to no exhaust sound, the pressure spike during combustion is so early, there's no pressure left when the exhaust valve opens (relatively speaking.) In my experience- random occasional misfires occur. Has a distinct "poot!" sound at the tailpipe, (reversion) once every 3-5 seconds or so. This is one of the major reasons I removed the EFI from the '90 f150: The base timing was 10*, but with the SPOUT plugged in, the ECM had it floating between 18-22+ degrees at idle, sounded terrible at the tailpipe, with the occasional misfires described above.

 

[Kritas]

I pulled the carb and opened it up per the pics in the thread on modding it to remove the SCV ports. I wasn't prepared for finding a bunch of brown sludge in the fuel bowl since I pulled the carb after purchasing the car to perform all the bench adjustments on it that the PO didn't do. The carb was clean at that time. All that gunk has sneaked by the fuel filters in the handful of minutes that I've had the engine running. I'm going to need to drain the tank and check it. I have no idea what that gunk could be, but I haven't added any gas since buying the car-not running.

At any rate, here's two photos with the holes that I think need to be plugged circled. I want to make sure this is right because the pics in the original thread aren't very clear. I've also attached part of the original thread on modding the carb. Should the hole on the right in the second pic be plugged along with the one on the left, or is it the one in the middle that should be plugged? They are different sizes. Plugging the one on the right would seem to block all vacuum from the fitting going to the distributor.