Poor Performance - Suspect resistance wire
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Intermediate
Joined: Apr 2007
Posts: 43
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From: Granada Hills CA
Poor Performance - Suspect resistance wire
My '67 with a 327/300 was running poorly. Long story short, the timing was messed up and could not be retarded enough. I pulled the dizzy and found the dimple was not lined up with the rotor electrode tip. Fixed that, installed dizzy, changed points and fired it up. Everything seemed fine until the test drive...
At about 2800 RPM the engine stumbles / misfires. Verfied the power valve in the carb was not blown out by turning down the idle screws and stalling the engine. This really feels like an electrical problem, not carb.
I checked all the spark plugs and wires...All good. I noticed the coil terminal and wire had some minor corrosion. I started doing checks on the coil per the service manual and found 12v at the positive side of the coil with the ignition in the "on" position. The service manual states, "If battery voltage of 12v is obtained, the starter solenoid is by-passing the high resistance wire connected between ignition switch and positive terminal of coil, thus the starter solenoid is not functioning properly to bypass the ignition resistance wire or the ignition circuit is incorrectly wired".
Has anyone ran into this and how is it fixed? Do I just put on a new solenoid? The car did not have this problem prior to pulling and re-installing the dizzy. I did incorrectly wire a remote starter on the solenoid for a few seconds but no sparks or obvious damage was observed. Any input would be greatly appreciated.
At about 2800 RPM the engine stumbles / misfires. Verfied the power valve in the carb was not blown out by turning down the idle screws and stalling the engine. This really feels like an electrical problem, not carb.
I checked all the spark plugs and wires...All good. I noticed the coil terminal and wire had some minor corrosion. I started doing checks on the coil per the service manual and found 12v at the positive side of the coil with the ignition in the "on" position. The service manual states, "If battery voltage of 12v is obtained, the starter solenoid is by-passing the high resistance wire connected between ignition switch and positive terminal of coil, thus the starter solenoid is not functioning properly to bypass the ignition resistance wire or the ignition circuit is incorrectly wired".
Has anyone ran into this and how is it fixed? Do I just put on a new solenoid? The car did not have this problem prior to pulling and re-installing the dizzy. I did incorrectly wire a remote starter on the solenoid for a few seconds but no sparks or obvious damage was observed. Any input would be greatly appreciated.
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Joined: Jun 2006
Posts: 90
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From: SF Peninsula CA
Power from your ignition switch is routed through a ballast resister, to reduce voltage and current to your coil and points. While starting, the solenoid provides the coil with a full 12 volts, bypassing the ballast resister. If your solenoid was defective or was wired wrong, you would not be able to turn the engine off with the ignition switch. 12v at the coil may not be good for the longevity of your points and coil, but probably would not cause the stumbles and misfires.
Race Director
Joined: Nov 2000
Posts: 10,340
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From: Beverly Hills (Pine Ridge) Florida
Seeing 12 volts at the coil depends on if the points (when the engined stopped) has the points open or closed!!!!!!!!!!
If the points are open, then I would expect to see 12 volts at the coil, since there is "no load" on the coil circuit. Short (or close) the points, and see if the voltage drops to 6-9 volts before jumping to conclusions. If you still see 12 volts (with the points closed), then you do have an "issue" of effectively running all the time with 12 volts to the coil.
BUT, this provides more ignition secondary voltage and is rarely a cause for misfire. It will burn up the coil in due time (more voltage equals more heat, and therefore less life), and the points would not last as long.
Plasticman
If the points are open, then I would expect to see 12 volts at the coil, since there is "no load" on the coil circuit. Short (or close) the points, and see if the voltage drops to 6-9 volts before jumping to conclusions. If you still see 12 volts (with the points closed), then you do have an "issue" of effectively running all the time with 12 volts to the coil.
BUT, this provides more ignition secondary voltage and is rarely a cause for misfire. It will burn up the coil in due time (more voltage equals more heat, and therefore less life), and the points would not last as long.
Plasticman
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
The Serivce Manual also tells you to disconnect the coil primary wire before you hook up a remote starter to prevent damaging the resistor circuit. I don't know if that's why you have 12 volts at the coil or not. If it's the solenoid, it would have to be broken or damaged to cause this.
You have two wires going to the primary side of the coil. One comes from the switch and one from the solenoid. Check each individually for voltage and find the source of 12 volts is where I'd start.
I'd look in the distributor for your engine miss.
[QUOTE=dyadon;
The service manual states, [B]"[/B]If battery voltage of 12v is obtained, the starter solenoid is by-passing the high resistance wire connected between ignition switch and positive terminal of coil, thus the starter solenoid is not functioning properly to bypass the ignition resistance wire or the ignition circuit is incorrectly wired".
You have two wires going to the primary side of the coil. One comes from the switch and one from the solenoid. Check each individually for voltage and find the source of 12 volts is where I'd start.
I'd look in the distributor for your engine miss.
[QUOTE=dyadon;
The service manual states, [B]"[/B]If battery voltage of 12v is obtained, the starter solenoid is by-passing the high resistance wire connected between ignition switch and positive terminal of coil, thus the starter solenoid is not functioning properly to bypass the ignition resistance wire or the ignition circuit is incorrectly wired".
Last edited by MikeM; Jun 4, 2008 at 07:07 AM.
