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Old 01-18-2021, 10:20 PM   #21
JSeery
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Default Re: Manifold vacuum at idle... vs without...interesting observations

Charlie, isn't carburetor base manifold vacuum?
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Old 01-18-2021, 11:07 PM   #22
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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Charlie, isn't carburetor base manifold vacuum?

I'm not Charlie but to answer your question, if the carb base port is drilled to pull from below the butterflies, it's manifold vacuum.

Awesome discussion people, I am enjoying it immensely, I just got back in from the shop. More later.

Cheers
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Old 01-18-2021, 11:15 PM   #23
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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If it was the one used with the Load-a-Matic distributor it has different passages for the dist. vacuum and will give you a venturi vacuum signal.

Only if you don't modify the carb. I plugged the venturi feed and only left the ported hole open just above the butterflies to give me straight ported vacuum...then realized I wanted manifold vacuum, for all the reasons discussed.


I know these are flathead engines, but read thru this article.


Cheers
Attached Files
File Type: pdf Vacuum_Advance_Specs.pdf (243.1 KB, 16 views)
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Old 01-18-2021, 11:19 PM   #24
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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What cam do you have in the engine?

I don't know yet, but I may pull a head and see if I can figure it out by valve movement..but not for a while. Found a 4 bbl Offy manifold and Carter WCFB carb...woo hooo


cheers
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Old 01-19-2021, 07:24 AM   #25
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Default Re: Manifold vacuum at idle... vs without...interesting observations

JSeery #21.............absolutely.....It has always been my understanding that below the plates is manifold vacuum. If a convenient port in the carb base is not available use or
provide a port in the intake as close to the carb as possible. Dunno about that, it's what
I heard.
The max adv adjuster I feature is very similar to what is shown...but not as tidy...6-32 allen as well.
Audio, photos, time for a video....Kilo
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Old 01-19-2021, 11:52 AM   #26
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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Audio, photos, time for a video....Kilo
Charlie ny
This was a few days ago right after I timed it and got it setup moderately well.

cheers

https://www.dropbox.com/s/6p5142j2v6...tuned.wmv?dl=0
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Old 01-19-2021, 03:39 PM   #27
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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No myth involved. Ported spark was developed to reduce exhaust emissions. I worked on engine development in the auto industry in the 60's and 70's. Ported spark was a way to reduce hydrocarbons before better systems were developed. Back then, engines didn't run worth a damn because of this and other attempts to reduce emissions.
So... what about the Fords '57 and up that used ported vacuum? That wasn't done to reduce emissions... and all the other 50s' and 60's engines GM and Chrysler that used ported vacuum? In that era the only emission controls used was a PCV valve, if that.
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Old 01-19-2021, 03:42 PM   #28
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Default Re: Manifold vacuum at idle... vs without...interesting observations

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Originally Posted by Kilohertz View Post
Only if you don't modify the carb. I plugged the venturi feed and only left the ported hole open just above the butterflies to give me straight ported vacuum...then realized I wanted manifold vacuum, for all the reasons discussed.


I know these are flathead engines, but read thru this article.


Cheers
Just didn't know if you had modified the carb... you were way ahead of me on that.
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Old 01-19-2021, 04:33 PM   #29
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Default Re: Manifold vacuum at idle... vs without...interesting observations

OK, so this discussion has raised my curiosity and I went out and grabbed a couple of non-Ford carb/intakes off the shelf. First one was the stock intake from a '62 Cad with the steel vacuum line still attached; traced the circuit in the 4GC base and it comes out below the throttle blades, manifold vacuum.

Then grabbed the set-up off of a '54 Cad, traced the vacuum passage and it comes out above the throttle blades, ported vacuum. So some variation here...

I'm not debating the merits of ported vs. manifold vacuum advance here, every engine is different and you'll have to experiment with it. Just the idea that ported vacuum didn't appear until smog controls...
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Old 01-19-2021, 07:05 PM   #30
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Default Re: Manifold vacuum at idle... vs without...interesting observations

Just as a matter of interest since we're talking vacuum. Someone may correct me if Ive got this wrong I was told our Falcon GTHO's in Aust had both ported and manifold, no doubt to do with starting a high comp engine.

Also the effect of vacuum, today here is very humid and sticky noticed I was barely getting over 20Hg on a cool crisp clear morning I will get close to 22 Hg.
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Old 01-19-2021, 09:24 PM   #31
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Default Re: Manifold vacuum at idle... vs without...interesting observations

Kilo,
That exhaust is a scream......you may have started a whole new performance
arena.....installation of hi-po vacuum fans to help pull the exhaust out of the motor....
super evac vs super charging.
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Old 01-25-2021, 11:36 AM   #32
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Default Runs better now...but why

So my Dad came over to hear the flathead again after I got her tuned up, and I was mucking about with the timing light trying to figure out the advance curve on the mechanical springs with the vacuum can disconnected and his first comment is..."it sounds like it is retarded". One thing I have noticed is it has a hard time accelerating without stumbling and you kind of have to ease into the throttle to get it up to 2,000RPM, I figured I needed to adjust the accelerator pump. He said no, lets check the timing, but I assured him I had it set to the mark on the crank pulley and he said forget that, lets time it by ear. I loosened the clamp and we spun it around until the idle smoothed right out and when accelerating it jumped right up like it was a new engine! Ran great! So for grins I put the timing light on it and it was at about 10-12* advance at idle, and made it to 21* at 2500 RPM, this was still with the vacuum can disconnected. Well what the heck? My Dad used to hot rod these engines back in the 50's and knows them very well, way to go Dad, thanks!

Now this crank pulley looks like it has been changed, it is new, with a little bit of surface rust on it....is it possible it's marked wrong, or is the wrong pulley? Anyone else find this? I am not sure if I can accurately determine TDC without pulling a head off, and even then, there is a fair amount of crank* movement while the piston is at TDC.

For now I'm leaving it as it as it runs so well, but ultimately would like to know what is going on with the marks on the pulley and why it runs so good at this advance setting.

Cheers
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Old 01-25-2021, 12:11 PM   #33
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Default Re: Manifold vacuum at idle... vs without...interesting observations

Kilo,
This happens all the time.........had '51 Merc in the shop with lag complaints,
timing was on the money mark wise, reset the dwell, changed the accel pump all for
nothing. I bumped the timing up a bit, took the Merc out it was better ,4th trip out it was real happy....same thing ,the pointer and mark were way off, but the Merc ran like it should....I remarked the pulley.
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Old 01-25-2021, 04:15 PM   #34
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Default Re: Runs better now...but why

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Now this crank pulley looks like it has been changed, it is new, with a little bit of surface rust on it....is it possible it's marked wrong, or is the wrong pulley? Anyone else find this? I am not sure if I can accurately determine TDC without pulling a head off, and even then, there is a fair amount of crank* movement while the piston is at TDC.

Cheers
Fairly easy to check/establish TDC with the heads on. There have been several threads on the process and I think Mart did a video. Basically you insert something through the spark plug hole that the piston can bump up against (something soft enough to not damage anything). The head of a zip-tie works. Then establish a pointer near the crank pully, turn the engine over until it stops against the object in the cylinder. Mark the position on the pully. Turn the engine in the opposite direction until it again hits the stop, mark the pully. TDC is halfway in between the two marks. Several repeats is good to verify your marks. Attempting to establish TDC at actual TDC is difficult because there can be a lot of crank movement with little noticeable piston movement.
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Old 01-25-2021, 10:49 PM   #35
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Default Re: Manifold vacuum at idle... vs without...interesting observations

Thanks boys for the replies. Interesting Charlie, QC? what QC? Oh boy, thankfully things have improved over the years.

Jseery, cool idea for finding TDC. I will try it tomorrow when I get a moment. It will be interesting to see how far off the pulley mark is.

Happy the engine is running so well. Oh, and the compression seems normal again at ~100psi. Seems one of my gauges was out of calibration and the other had a faulty Schrader valve.

Cheers
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