11-05-2021, 04:32 PM | #1 |
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Vacuum guage
I got a vacuum guage and plugged it into the 51 Merc in my ‘39 Ford. I had the carbs set pretty close by ear. Set the timing by the gauge and ooo did that change the sound of the old beast. Most importantly it pulls a nice healthy 20 inches and very steady. Happy
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11-05-2021, 05:00 PM | #2 |
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Re: Vacuum guage
Have you driven it yet? I've no idea what a '51 Merc wants, but typically more modern engines need to have the internal advance mechanism tailored for that on the far end or it will be Ping City. Flatheads don't want or tolerate near as much ignition advance as OHV engines either so I'm curious.
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11-05-2021, 06:52 PM | #3 |
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Re: Vacuum guage
Well I’ll keep an ear out. And I’ll get out the timing light. What’s the dwell? I got one of those dwell tach thingies that I’ve had for next to ever.
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11-05-2021, 07:20 PM | #4 |
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Re: Vacuum guage
Dwell is a more accurate way to set breaker points. Theoretically when the points are set with a feeler gauge to spec the dwell is also at the correct spec. Ford cautioned this only applies when installing new points, once they start to wear after run-in, using a feeler gauge alone would be inaccurate as the point faces are no longer flat.
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11-05-2021, 11:07 PM | #5 |
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Re: Vacuum guage
qTalking vacuum gauges. All combustion engines are just air pumps. How much air you move effects fuel. probably heard this saying before, there is no replacement for displacement. Spark and timing is independent somewhat to vacuum, if it's not controlled by vacuum. Internal engine pressure is not always effected by compression, pretty much the internal vacuum is around 18-20 from 32-53 and beyond. Your highest vacuum reading will be at idle.
air-fuel-spark. If you are not optimizing best vacuum, you may have a leak or bad rings/valves/etc. No amount of spark will help that. Certainly all has to be in concert. No one thing makes the other not matter. Last edited by Tinker; 11-06-2021 at 03:12 AM. |
11-06-2021, 07:49 AM | #6 |
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Re: Vacuum guage
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11-06-2021, 08:19 PM | #7 |
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Re: Vacuum guage
I just went through the same thing today! Dropped in a Mallory duel point and used a vacuum gauge to dial it in, sounded great at idle but test drive it pinged as soon as I put my foot to it. Took 3 adjustments to get rid of pinging, now it dies when I put it in gear? still playing with it?
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11-06-2021, 09:37 PM | #8 |
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Re: Vacuum guage
setting ignition with vacum gauge will give you a starting piont often it will be advanced from stock you still have to workout your total advance and at what rpm remember todays fuel has almost nothing in common with the fuel of 60 years ago other than its name
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11-06-2021, 09:49 PM | #9 | |
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Re: Vacuum guage
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11-06-2021, 10:12 PM | #10 |
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Re: Vacuum guage
I’ll check tomorrow
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11-06-2021, 10:20 PM | #11 |
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Re: Vacuum guage
One other thing. I put a dual point Mallory in one of my engines a while back. It didn't run very well, so I checked the point gap, which agreed with the instruction sheet. On a hunch, I dug out my old dwell meter and checked the dwell, and it was way short. After carefully setting the dwell (which can be a fussy procedure), the car ran great. I believe that I had the wrong instructions or they were incorrect; either way, I now always use the dwell meter to set the points.
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11-07-2021, 06:37 AM | #12 |
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Re: Vacuum guage
Fussy is right! Especially if the distributor is tucked back tight up against the firewall and you haven’t done this often. At least it’s easy access to later model flathead’s.
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11-07-2021, 11:32 AM | #13 |
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Re: Vacuum guage
So the dwell is between 26 and 27, I’ll call it 26 1/2, I’ll not mess that up. What I supposed was timing bump on the crank pulley that I painted yellow is not insight using the front passenger side cylinder. I moved the distributor and the timing light but still no dot.should the pointer be at about 11 looking from the front? I do see some advance from the distributor. Not sure how many degrees, the scratch that was visible moved maybe an inch and a quarter when I revved it up to about 2000 rpm.
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11-07-2021, 06:04 PM | #14 |
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Re: Vacuum guage
"26 and 27"? I am away from all of my documentation, but I thought the dwell should be around 36 degrees.
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11-08-2021, 12:03 AM | #15 |
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Re: Vacuum guage
To add to my post before. If your engine vacuum is not tuned it will have an effect on all systems like vacuum dizzy advance and wipers.
If your engine vacuum is 15. It will effect your vacuum advanced dizzy. Dwell will just fine tune it more. I would achieve good solid vacuum readings from the holes in the motor first (like adjusting carbs) then tune a bit. Last edited by Tinker; 11-08-2021 at 12:44 AM. |
11-08-2021, 06:43 AM | #16 |
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Re: Vacuum guage
I just looked up dwell with a search on this site and 27 is the right number. Next project is to find out why the pimple that I painted yellow is nowhere in sight of the timing light flash.
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11-08-2021, 09:42 AM | #17 | |
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Re: Vacuum guage
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11-08-2021, 09:47 AM | #18 |
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Re: Vacuum guage
Sorry; the 36 degrees is for a dual point Mallory. I believe 27 is correct for a stock distributor; (I lost track of who was posting what.) Seeing that the timing mark can't slip (like on a harmonic balancer), are you sure you have the timing light lead on the correct (#1) plug wire?
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11-08-2021, 10:15 AM | #19 |
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Re: Vacuum guage
Is it possible to check dwell with the distributor off of the engine; and not having any kind of distributor machine? The idea of tweaking the points adjustment on an early flathead if you have to run the engine between adjustments is quite discouraging.
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11-08-2021, 05:41 PM | #20 | |
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Re: Vacuum guage
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