Timing issues

I recently replaced a failed distributor pickup coil and found my timing was some 20 degrees late. Turning the housing to bring it back to 8 btdc resulted in severe backfiring when I tried to drive it. I discovered the fire was going out around 25 degrees of total advance which let the fuel flow into the exhaust until it slowed down enough for the ignition to fire and boom, pow, pop, you get the picture. Turns out the centrifugal advance was moving the rotor far enough ahead of the spark plug terminal in the cap that spark could no longer reach the plug terminal. The breaker plate or I suppose pickup plate is positioned by the vacuum advance and I could find no difference between the new and old pickup so I drilled a hole in the vaccume advance arm to move the plate, and thereby the point at which it fires the coil closer to the spark plug terminal. Now I realize this is a pretty redneck solution but I'm at a loss to explain why there is such a difference. Mid 70s ford distributor, MSD 6al box that replaced a Mallory unit. Has a Mallory square ignition coil so it's kinda a hodgepodge of components but I'm not sure any of them are smart enough to know what the trigger is, or whose coil or distributor cap delivers fire to the plugs. When I set the crank on 8 degrees btdc and check the reluctor position in relation to the pickup coil it is further past the iron core than is the next tang coming to the pickup. Would a ballast resistor in one of the wires going to the pickup coil reduce the strength of the magnetic field and cause it to trigger the spark earlier? The car runs fine as is but my fix seems kinda hokey even tho it works.

Having a really hard time following you, if i have this right, your timing was at 25* and now youre trying to set it to 8*? Seems like a drastic change, and the first number seems more realistic. What duration and lsa on the cam? When in doubt, its usually best to reset your timing from scratch. Disconnect vacuum, make sure mechanical advance isnt moving at idle. Advance timing to achieve peak idle vacuum, adjusting idle as you go, subtract your vacuum can from that, generally around 10* on a performance can, could be 15* or more on a stock can. That is your base timing number, remember it, doesnt have to be dead on but what were shooting for. Next you need to change the guts of your distributor to achieve the total timing you need while still coming close to your base timing number. For instance. My 351 im running 15* initial and 34* total, vacuum adds another 9* at idle.

The first sentence says it. I replaced the pickup and the timing was 20 degrees retarded. I moved the housing to set it back to 8 initial. I understand how to do all that and cam specs have no bearing. It ran well prior and does now after my hokey fix. But why did it change? I know it's long, but I think it is clear. It took me a minute to figure out what was happening, but the timing light clued me in when around 2500 rpm the light went out. No fire to the plugs.

lvhdude wrote:The first sentence says it. I replaced the pickup and the timing was 20 degrees retarded. I moved the housing to set it back to 8 initial. I understand how to do all that and cam specs have no bearing. It ran well prior and does now after my hokey fix. But why did it change? I know it's long, but I think it is clear. It took me a minute to figure out what was happening, but the timing light clued me in when around 2500 rpm the light went out. No fire to the plugs.

Double check to make sure pickup is wired correctly.. IF the wires were switched in the connector, it could cause a difference in timing..
Also check resistance of new pickup...just because it is new, doesn't mean it's good..

I did check the resistance, 550 ohms. Within spec. I think is 400 - 800 ohms. The old pickup had a purple and an orange wires to the actual coil. The new is red and black. It came to me with a connector for a Mallory system that I made sure to match polarity when I replaced the Mallory with a 6AL MSD box that was a year ago. I'm not sure the field created by voltage flowing through the winding would change the timing event no matter the polarity. Have you seen that to be true?

lvhdude wrote:I did check the resistance, 550 ohms. Within spec. I think is 400 - 800 ohms. The old pickup had a purple and an orange wires to the actual coil. The new is red and black. It came to me with a connector for a Mallory system that I made sure to match polarity when I replaced the Mallory with a 6AL MSD box that was a year ago. I'm not sure the field created by voltage flowing through the winding would change the timing event no matter the polarity. Have you seen that to be true?

I have...

QtrWarrior wrote:

lvhdude wrote:I did check the resistance, 550 ohms. Within spec. I think is 400 - 800 ohms. The old pickup had a purple and an orange wires to the actual coil. The new is red and black. It came to me with a connector for a Mallory system that I made sure to match polarity when I replaced the Mallory with a 6AL MSD box that was a year ago. I'm not sure the field created by voltage flowing through the winding would change the timing event no matter the polarity. Have you seen that to be true?

I have...

If I remember correctly MSD even mentions the wires being crossed in their trouble shooting instructions.

lvhdude wrote:I recently replaced a failed distributor pickup coil and found my timing was some 20 degrees late. Turning the housing to bring it back to 8 btdc resulted in severe backfiring when I tried to drive it. I discovered the fire was going out around 25 degrees of total advance which let the fuel flow into the exhaust until it slowed down enough for the ignition to fire and boom, pow, pop, you get the picture. Turns out the centrifugal advance was moving the rotor far enough ahead of the spark plug terminal in the cap that spark could no longer reach the plug terminal. The breaker plate or I suppose pickup plate is positioned by the vacuum advance and I could find no difference between the new and old pickup so I drilled a hole in the vaccume advance arm to move the plate, and thereby the point at which it fires the coil closer to the spark plug terminal. Now I realize this is a pretty redneck solution but I'm at a loss to explain why there is such a difference. Mid 70s ford distributor, MSD 6al box that replaced a Mallory unit. Has a Mallory square ignition coil so it's kinda a hodgepodge of components but I'm not sure any of them are smart enough to know what the trigger is, or whose coil or distributor cap delivers fire to the plugs. When I set the crank on 8 degrees btdc and check the reluctor position in relation to the pickup coil it is further past the iron core than is the next tang coming to the pickup. Would a ballast resistor in one of the wires going to the pickup coil reduce the strength of the magnetic field and cause it to trigger the spark earlier? The car runs fine as is but my fix seems kinda hokey even tho it works.

When the timing is correct ... the rotor phasing is way off.
This sometimes happens when a pick-up in the distributor is replaced, the magnet under it is installed up-side down giving the wrong polarity. The later pickups are usually riveted to the magnet though to keep this from happening.
The wires could be reversed as has been said, which is most likely.

The issue IS rotor phasing, though.

QtrWarrior wrote:

lvhdude wrote:I did check the resistance, 550 ohms. Within spec. I think is 400 - 800 ohms. The old pickup had a purple and an orange wires to the actual coil. The new is red and black. It came to me with a connector for a Mallory system that I made sure to match polarity when I replaced the Mallory with a 6AL MSD box that was a year ago. I'm not sure the field created by voltage flowing through the winding would change the timing event no matter the polarity. Have you seen that to be true?

I have...

With a 6AL and a Ford pick-up the wiring is not obvious as the purple wire connects to orange and the violet wire connects to green.
The two purple/violet wires do not connect together.
You said your wire leads are red and black so, you will need to figure out which is positive and which is negative.

The wires would usually be the correct polarity when the ignition timing is the most retarded.

DING DING DING DING! We have a winner! QtrWarrior called it. I would have bet hard cash the polarity wouldn't make a significant difference. It's been a couple days til I had time to swap the outside pins in the Mallory connector that I spliced onto the new pickup coil and even after i retarded the distributor twice to get it started it was at 35* advanced. Turned the distributor back some more, moved the vacuume advance arm back to the regular mounting hole, set timing at 6*, and then brought the crank to 6* on #1 and found the MSD box is now firing right when the reluctor tang is in line with the iron core of the pickup coil, and the rotor now is very close to center of the#1 terminal on the cap. Rmcomprandy thanks for your input, what I found was the reversed polarity retarded the ignition event so severely that the rotor became so far out of phase it would virtually not run. My hokey fix compensated enough to be driveable but it does run smoother after correcting the polarity. Thanks everybody.