Hmmm. I believe you right!
Wilcox's diagram has a mistake.
Points ground the coil.

GM sourced Diagram?

 

Thanks anyway! I’m still getting too high of voltage at the coil when running. Maybe the wire from the starter is wired incorrect?

 

Could be. Post a pic.

The yellow wire to the coil +, from the starter should give 12V. It comes from the "R" terminal. But it should shut-off to zero V when the starter releases / is not turning.
Maybe something in the solenoid is sticking?
Should be an easy test.

At the solenoid the yellow and purple wires should be on opposite small studs, not the big center red battery one. Correct solenoid has 3 studs, two small, one big center. Later HEI cars have a solenoid with no R stud, it's not needed. Purple wire is only hot, 12V, when key is in Start position. Does not even have to hooked up to starter. Juice comes from ignition switch on steering.

If you apply 12V to the "S" stud, the solenoid should click, and then the "R" stud should also have 12V now. Release power to S and R also releases. You could disconnect the main batt, and use a small test batt. Not as intimidating. Starter will only try to crank engine if big batt is connected to big stud.

Careful of that big center wire, it is hot all the time, direct to big battery, no fuse, no fusible link no relay!! Short it out while testing and you can weld stuff, like screwdrivers! BTDT. LOL. I do some testing now with the main battery or cable unhooked, or even replaced with a small 9 Volt, or motorcycle batt, cordless batt pack, etc in batt box, or on floor, if needed. Much safer. At least until I know the start circuit works as intended.

The other + coil wire (white resistor one) should give less volts than 12 (7V?) anytime the ignition is in Run or Start position. Only zero when ignition is off, or accessory. Should also be an easy test, with a voltmeter. Juice should come from dash and the ignition switch.

I have heard that points will burn quickly if run with 12V all the time. (Too much sparking I guess).

If not that, I guess the ignition switch on the column could be hooked up wrong too. Tracking the 12V flow should find your issue.

 

Thanks, Leigh. This makes sense, I knew the voltage dropped at some point on the wire from the starter but just didnt know the mechanism. This sounds very “traceable”.
If the points weren’t burnt out from the over voltage could this cause a miss or only at the point that the distributor points are damaged?
The reason I ask is that I replaced the points were replaced and I still have the miss.
KC

 

The points are just a ground to trigger the coil. If they are burnt, resistance is high, and may not get a good ground, coil may not trigger right. This all happens in milli seconds. ~2800 rpm is usually one of the leanest points in the engine's afr range, and where the ignition requirements increase the most. If the ignition system is not 100%, missing there is common.

The condensor helps protect the points too, did you change that as well?

There is a tool (cheap) that will help you test the length of spark aka: ignition or coil output. 2" sparks are very entertaining! It's a good tool to stress the coil and ignition system output. If the spark just suddenly stops, or jumps somewhere else, you can usually see or hear it. LOL If the coil is breaking down, it'll just quit, too soon, and only make little sparks.

 

I’ll get one of those tools. It’s very interesting you mention the 2800 rpm range as that one of the worst ranges for my current miss!
I really appreciate your help as I’m a non pro mechanic and we don’t have quality vintage car mechanics in our rural area. It’s up to me so i have no choice but to learn. Most of these mechanical concepts are simple but can get complicated at the same time.
KC

 

Well, I'll be! Never saw that tool before so did some digging. Lisle sells one ~$30 but less expensive import brands are available too. Lisle also sells another more simple version. Here are the instructions from an Amazon review:

 

Is it possible for an issue with the alternator to be causing an over voltage at the coil with the engine running. I’m reading about 13.4 at the positive side of the coil with the engine running. If not I’m going to take a look at the solenoid.
KC

 

Just took a photo out of my manual and want to point out that the RED feed to positive on coil from ignition should be through a ballast wire. This would be the supply with engine running. The blue feed is from the starter for starting only and should disconnect once the starter stops cranking.

I wonder if you’re seeing full volts at coil AFTER start either the feed from starter is still engaged OR the ballast wire has been replaced or bypassed to full battery voltage?

 

I know you want to keep it all original and I fully understand that, I was the same, but you can put a Pertronix III in that distributor and add matching coil and it seriously transforms these cars. Best thing I ever did to my 1971. Easy install.

 

Did you change the timing along with adding the Pertronix? I'm curious how this transformed the car in any way.

 

Hi Bikespace, it was an evolution process, so I was staunch keep it all original. Loved the reliability of points and bought a dwell meter, had it all tuned in. I then obtained Lars papers and followed them accurately including importing from the US one of his recommended vacuum canisters and modifying it to limit it’s advance. I connected it to manifold vacuum. I then lightened the dizzie springs so 36 all in by 3000. This made the car drive great! I still had a slightly rough idle and put it down to slightly stretch timing chain and worn vertical bushes in the dizzie, so pulled it, and Re shimmed it. While out, thought I’d try an electronic solution. Designed a little circuit that run 12v from horn relay to coil triggered from a relay powered from the spare ignition spade on the fuse box. Overkill yes! Findings were better idle, and cleaner burning engine, less fumes when idling at the lights. Excellent acceleration and better fuel economy which obviously is a result of extra performance. Placebo maybe but I’m very happy with the overall result of Lars amazing knowledge (he is a true hero!) including his help with my Qjet and the addition of a maintenance free apparently multi spark unit. Edit, also followed Lars advise of lightening the Qjet accelerator springs/s

 

Thanks for that! So following @lars' tuning instructions made your car run like a champ!

That was my experience, too, with two HEI C3s. I'd say the Pertronix had nothing to do with it, but it gave you an excuse to use a Lars-style tune, which many on this Forum can confirm, really wakes up these cars!

 

The wiring is original. Im out of town but now thinking I may have connected the start and run wires incorrectly at the starter solenoid.
KC

 

I hope it's something simple like that!

Please post some photos of the before and after if you change anything. Especially if it fixes it!

 

I would think 13V constantly , to the points, would burn the point contacts after some period of time. Then you get high resistance, and the coil may not get a clean signal or fire as well. Low coil spark energy would show up first, when it is stressed the most, at the carb's leanest cruise point ~2800 rpm.

It's one possible theory, anyway.

Let's see, the coil actually charges with current flow thru the points, it fires when that flow is cut.
So if the point resistance is high, the current flow is too low, and the coil does not get fully charged, and a weak spark is the result.

The logic explains your situation. And the coil output tester (Lisle?) should prove a weak spark.
I suppose an ohm meter across the point contacts would prove high resistance as well.

I do remember back in the day, we would run a file thru the points contacts, and the car would instantly run better.

The real question is why is it getting 13V all the time?
Starter mis-wiring? maybe... Or resistance wire replaced with regular wire? maybe more likely...or damaged coil? also likely

 

The resistance wire looks stock so I’m thinking it is wired incorrect at the starter, I hope to check that tomorrow. I have tried two other new coils and no improvement.
KC

 

With engine running, get a volt meter and measure that wire on the solenoid ‘output’ to ground on your chassis. If it’s reading anything, something is wrong. As others have said, the points will have a short life expectancy seeing full voltage all the time.

I hope you get it sorted. I feel you’re pain as I had a fuel pump failure (1 1/2 year old Carter) that presented as an electrical fault only when the car was real hot. It would start and run normal but when hot, misfire and die on acceleration. It was the one way valve on the ‘pump to carb’ side of the circuit. It had fallen off inside the pump. My guess is when the fuel was cold and the Qjet secondary lockout engaged, the car had enough (in float chamber) dense fuel for normal driving. Once hot, vapour lock started to play and secondaries helped drain the float chamber dry. Try starting the car again and all good till next WOT. Best of luck!

 

Update:
I got the starter removed to inspect the wiring at the solenoid, it appears that I had it wired correct. I did notice one crimped and one bare place in the “run” resistance wire. Would it be ok to cover this section in a piece of heat shrink tubing? The start wire looks to be in good condition.it would be great if someone could look at the pictures and double check the connections.
KC

 

Gday Grumman41, here’s a photo of mine which should be the same setup as yours. Mine is a base 350 but concept is the same.

yours looks setup correctly but you mentioned ‘resistance wire’. It should be a normal wire with no resistance ie no ballast.

the ballast wire should come out your firewall from your fuse box.

sequence of event at starting.
- when you turn key, starter solenoid triggers that ‘R’ wire (not resistance &#128522 and sends full voltage for helping the start.

- when car starts, you release the key and starter disengages, starter solenoid switches OFF that ‘R’ feed to coil and the ballast wire with its reduced voltage 7volts??? sustains voltage to coil and is low enough to reduce points burn out.

someone please correct me if I’m wrong.

I think you still need to test ‘R’ wire with engine running to see its switched OFF. Set volt meter to 20v DC, probe the ‘R’ wire and probe case of starter or chassis. Should read zero.

As you can see, mine doesn’t have heat shrink either.