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How many effective spark positions?

Posted: Wed Nov 20, 2024 10:23 am
by Steve Jelf
I believe Murray Fahnestock's chart of spark and throttle settings applies only to driving on BAT. On MAG the number of effective spark settings is limited. Are there three, or four?

SPARK-THROTTLE DIAGRAM.jpg

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 10:38 am
by TXGOAT2
On mag, you will have 2 or 3 "null spots" within the spark lever's range where magneto output is near or at zero. They are very narrow, with mag output increasing to either side as the lever is moved. Likewise, you'll have 2 or 3 spots where mag output is at the maximum, with decreasing output either side of them. For starting, it's best to put the spark lever close to a maximum mag output point consistent with suitable timing for starting. Experimentation could reveal the maximum output points, or running the engine a little above idle and connecting an AC voltmeter to one of the coil primary wires, then moving the spark lever through its range, ought to give a good idea of where the maximum mag output "hot spots" are located on the spark lever. Every car will be different. On battery, the current supply is constant, so coil output will be very nearly constant throughout the spark lever's range.

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 10:40 am
by TXGOAT2
Ford suggested that, for starting on magneto, advancing the lever a few notches might give better results when starting. Obviously, caution would be needed, especially if hand-cranking. Again, every car will be different.

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 10:44 am
by TXGOAT2
Retarding the spark for mud or hill climbing is rarely necessary today, since even cheap gasoline is usually 87 octane or higher. That was not true back in the day, and "spark knock" had to be guarded against on heavy pulls. Only at very low engine speeds with the throttle open well above idle would retarding the spark be necessary today.

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 11:05 am
by Norman Kling
I have found the best positions for the maximum spark. Then took a little white paint and put a mark on the quadrant so I can find it without having to experiment every time I drive.
Norm

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 11:38 am
by TXGOAT2
Good idea!!

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 12:28 pm
by Dan Haynes
If your timer is set to start on battery, the full retard position of the lever is all but useless for magneto operation. As you advance the spark, the first useful current spike happens about 5/8" down from the top. The second (useful) one, about half way through the sweep of the lever, is good for slow speeds in high pedal and for pulling hills if the engine begins to struggle. When the lever is at about 7 o'clock is full advance where it spends most of its time. On my car, you can pull the lever farther, straight down to 6 o'clock, but that is not a useful setting. It's too far advanced and the engine vibrates.

So by my count:

1. Full retard, useless for magneto use.
2. Good for easy starting on mag.
3. Slow driving or heavy going.
4. General driving at road speed.
5. Good for nothing

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 12:40 pm
by jab35
This is the best article I have found on this topic, courtesy of Ron Patterson. jb

https://www.fordmodelt.net/downloads/Mo ... nition.pdf

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 3:36 pm
by NealW
Steve,

You unfortunately missed last January's Model T clinic, but there was an excellent ignition presentation by Larry Azevedo. Among other things, he talked about the spark setting when running on MAGNETO and that there is essentially one setting that works the best from idle to cruise speed. I seem to remember him showing data backing that up. I had never really thought about it before, but it made sense because once I adjust the spark setting, I rarely touch it while driving.

I almost always start our 11 set to magneto and hand crank (no starter) and may back off the spark advance a bit for starting, but never to fully retarded. I only retard it if using the battery to tickle the coils.

Neal

Here's a link to a video of his presentation:

https://www.youtube.com/watch?v=oB6LhiUBbMo

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 4:37 pm
by TXGOAT2
The timing will advance somewhat on magneto as engine speed increases due to higher mag output. I use the timing lever as needed when driving to get the best results.

Re: How many effective spark positions?

Posted: Wed Nov 20, 2024 7:27 pm
by Norman Kling
Actually, every car is not different! The difference is the type timer and initial setting of the timing rod.
We live in the mountains so almost everywhere we drive is either uphill or downhill. There are a few relatively flat places. So this is what I have found. I start on battery with the lever all the way up. As soon as it starts, I immediately switch to magneto. The best place for idle on mag is a few notches down. For 25 to 30 mph about half way down and for high speeds up to about 45 mph about 3/4 way down. When I come to a hill I try to go as fast as I can as I approach the hill and then it will usually go up in high gear with the spark about half way down. If I get behind another car going slower, I have to shift down or it will lug the engine. In low or Ruckstell I can advance the spark a bit. When I go down hill, I push the gas all the way up but leave the spark at least half way down otherwise it will pop and possibly blow off the muffler. There is one place I need to drive from time to time which is a divided highway with high speed limits. I approach at the closest ramp to the bridge and take the right lane and go as fast as the car will go for about 400' across a bridge and then take the closest ramp off. Fortunately there are ramps at both ends of the bridge so don't have to go that fast for long! Only other route would be a long way around through the mountains.
Norm

Re: How many effective spark positions?

Posted: Thu Nov 21, 2024 9:21 am
by TXGOAT2
Different timers, different coil settings, varying linkage adjustments, varying degrees of wear, and even how the car is sitting can affect the position of the lever to some degree. Other factors can make a difference, including elevation, engine condition, temperature, and even humidity. Another variable is the fact that many cars today lack notches on the lever quadrants.

Re: How many effective spark positions?

Posted: Thu Nov 21, 2024 9:39 am
by TXGOAT2
My car never pops back in the exhaust. I'm not sure why. I don't have mountains around here, but there is a 12% grade that I have to go down often, and of course it has a stop sign at the bottom. I go down it with the throttle closed. The car will gain a lot of speed unless I use some brake. The position of the spark lever doesn't have much effect. I have a New Day timer on the car. There is one other location that is about as steep, and it has no stop sign or cross traffic, but it has a 30 MPH curve, so there's a good distance that has to be covered with the throttle off.

Re: How many effective spark positions?

Posted: Thu Nov 21, 2024 10:39 am
by Norman Kling
If you have a steep grade like that with a stop sign at the bottom, shifting to low gear or if you have it Ruckstell or other auxiliary transmission low range just before you start down the hill. when shifting down advance the throttle to speed up the engine then raise the throttle after shifting for extra braking from compression of the engine. In fact Ruckstell will actually amplify the power of the transmission brake.
Norm