As I understand it, the Load-A-Magic Distributor uses only the Venturi vacuum from the carburetor to advance the spark. It doesn't use centrifugal weights. Is this correct? I don't have any Venturi vacuum at the carb regardless of RPM. It didn't occur to me until this evening that I may have a centrifugal weight distributor, so I haven't checked to see whether the spark advances with RPM.
I have never seen a distributor that is only vacuum advance. I don't see that as working too well. In a typical vacuum advance distributed with a base timing of 10 degrees. A centrifical advance of 18 degrees and a vacuum advance of 10 degrees for a total of 38 degrees. At full throttle(low vacuum) it would drop Back to 28 degrees.If you had a base timing of 10 degrees and a vacuum advance of 28 degrees to get a total of 38 degrees at high vacuum. At full throttle (low vacuum) it would drop back to 10 degrees. I expect if you put a timing light on it you will find it has at least some centrifical advance.
Which engine and carb do you have? You should not have a Load-a-Magic unit. Check this site thread out: http://www.fordbarn.com/forum/showthread.php?t=85865&showall=1
Early Falcons, and Rancheros I assume had Load a Matic distributors. Biggest problem with them was the advance diaphragm would go bad. You wouldn't even have to put a timing light on one to diagnose a bad one. They wouldn't pull the hat off your head when they went bad.
The FordSix.com page https://fordsix.com/ci/Loadomatic.html says it was used on "The Falcon Six" engine. It is a LOM distributor and the carb has the Spark Control Valve. I'm only getting .1" Hg of vacuum at the carb, and it doesn't change at all with RPMs. Also, it appears that the advance diaphragm is leaking because I can only move the distributor plate a tiny bit with a vacuum pump. The spark does not advance at all with any increase in RPMs. I can understand replacing the vac advance, but I'm stumped on the low vac at the carb.
And that .1" was at what port? See, vacuum is at various points depending on where the ports are positioned relative to the throttle plate or plates, as the case may be. If you measured the vacuum on a venturi port with the engine at 2500 RPM (the point where you check timing advance), and you have no vacuum reading, let alone .1", then that port is blocked for some reason. It could be carbon buildup or the wrong carb gasket, etc. Remember, full vac is in the intake below the carb base, transitional vac is just above the closed throttle plates, and venturi, of course, is where the discharge outlet is located, where the carb body meets the throttle body., or just a smidge above.
It was measured at the Venturi port - in the middle of the Venturi- well above the throttle plate. At idle manifold vacuum is 18". I ran a paper clip size wire thru the Venturi port and could see it emerge inside the carb. I don't see any other vacuum ports on the carb (like a ported-transitional vacuum). I'm thinking the problem might be the Spark Control Valve, which should allow manifold vacuum into the distributor vacuum line. But I can check the carb gasket, as it might be blocking the SCV passageways...
At least look at the carb body to throttle body gasket, unless you decide you want to go ahead and remove it, and the carb-to-intake gasket. But if you get no vacuum at the venturi port and it's not blocked, perhaps it's the wrong carb? The page I posted mentioned that a carb change would screw up the Load-a-Magic system. Is there a tag on the carb's airhorn?
There is no carb tag but I'm sure it's correct, I've compared it to numerous photos/diagrams. There should be no vacuum at idle, and the spark control valve is suppose to channel manifold vacuum to the distributor nipple on the carb as RPMs increase, so I've ordered a new SCV. If that doesn't help then I'll tear into the carb; there are a number of check balls, etc. in there, as well as the gaskets, as you say.
The Load a Matic system works on a very low vacuum signal. It starts to work at about a 1/2in of vacuum up to about 2in. It doesnt take much vacuum to make the system work. The carb takes 2 vacuum signals, one above and one below the throttle plate to control the advance. One function of the spark valve is to control the system so spark advance doesn't retard the timing, the other is to advance the timing using the "mix" of the vacuum signals. I would replace the distributor advance diaphragm before I would condemn the carb.
I can understand if you want to keep the car as original as you can, but if not, perhaps swapping to any electronic ignition would be a better use of the money you're now spending. All you'd need for Duraspark II is an '80s 200CID dizzy, spark box, coil and wiring between them. Or, if you went with Pertronix, a mid-Sixties inline six dizzy and the Pertronix unit with a Blaster coil.
True, and I may end up doing that, but the SCV was only $8, and vacuum advance $19; a small price to see if I can get it running right.
OK. But with what I read about Load-a-Magic, it's a load, alright, and zip point nil about it that's magic.
Measuring venturi vacuum is nearly impossible. The vacuum is created in a tube inserted into the venturi, the venturi does not create vacuum, it creates an increased air speed that translates into increased vacuum in the tube inserted in the venturi. A carburetor uses this process to meter fuel to the engine. The change in vacuum is subtle except when the engine is under load conditions that cannot be replicated when stationary unless on a dyno. I am not familiar with the Load-a-matic, but I do understand carburetors. The described system uses the same system that vacuum secondaries utilize, but rather than opening the secondaries, they alter the timing. So, just as you cannot set up secondaries in your driveway, (they will never open) you have the same dilemma with your system. I would T the vacuum line and use a long enough hose to get the gauge into the car. Then use a pipe cleaner or bread tie wrap affixed inside the distributor in such a way that it bends when the vacuum actuates and you can also tell how far it moved. (we do the same thing with secondaries, but the tie goes on the rod so that it slides when they open) Hope this is of help.
That makes a lot of sense to me. Last night I was just discussing with my son how the vacuum readings weren't correct because the engine wasn't under load, just high RPMs.
