Ignition problem on 70 Corvette 350/350

**Edward J.** · June 24, 2020, 06:14 AM

Re: Ignition problem on 70 Corvette 350/350

Steve the condenser wire almost appears like it’s hitting the base plate. I think you need to straighten those wires out anyway they should br on top of each other also the points spring is not slide all the way in.

**Stephen B.** · June 24, 2020, 06:20 AM

Re: Ignition problem on 70 Corvette 350/350

Steve,

I will check the condensor wire; however, I don't believe that it's actually touching. Also, the capacitor measures .376 mF.

**Gary B.** · June 24, 2020, 07:33 AM

Re: Ignition problem on 70 Corvette 350/350

Take 400-grit wet/dry sand paper, run it through the points a few times. The contacts develop a film, scum, corrosion over them from sitting on the shelf at the parts store. These are not a real high moving items for parts stores any more.
Gary B

**Duke W.** · June 24, 2020, 07:57 AM

Re: Ignition problem on 70 Corvette 350/350

NEVER use any kind of "sandpaper" on electrical contacts. The grit is non conductive. If necessary to dress contacts use a small file like a nail file.

Duke

**Stephen B.** · June 24, 2020, 08:42 AM

Re: Ignition problem on 70 Corvette 350/350

Thanks for all input. The question I have is dressing the points the logical next step?

**Larry M.** · June 24, 2020, 11:13 AM

Re: Ignition problem on 70 Corvette 350/350

With your multimeter, check that there is continuity between the distributor base plate and the distributor housing, and also between the distributor housing and the engine intake manifold. Record the resistance numbers you get. There is a black grounding wire between the condenser base and the vacuum advance can screw that can flex and break. If it does, distributor will not function.

The condenser lead wire is mounted upside down. Should have the opening in the wire terminal "U" pointing down and not up. And make certain that the condenser lead and the lead to/from the coil are arranged so that the "flat" side of each terminal is together, with the wire crimp side of each terminal facing away from each other. Minor points (issues),but just good practice.

You can also use electrical contact cleaner on the point surfaces, but a light pass with a points file and a wipe of lacquer thinner after should be fine.

Larry

**Mark E.** · June 24, 2020, 11:28 AM

Re: Ignition problem on 70 Corvette 350/350

What symptoms are you seeing? Won't start? Misses?

Would you clarify:

- "The points are not making a ground connection for the coil to receive voltage..." With the negative wire disconnected from the coil and the points closed, there should be continuity between the end of the wire and ground.

- "The coil has 12 volts at its positive terminal when I check the voltage between the positive terminal and ground." With the ignition ON, the coil should have about 9.5 volts because of the ballast resistor wire. With the ignition in START, the coil should have full battery voltage.

- "One issue I noticed is that when I set the breaker point gap initially to the .016" to .019" range, the points did not make electrical contact..." When points are open, they break the circuit. Is that what you mean by "did not make electrical contact"?

- "I adjusted the points to be slightly closer until I obtained continuity." Do you mean there was no continuity when the points were closed until you adjusted them with a smaller gap (i.e. they were not closing)? The circuit should be open when the points are open.

- "The points are new, Echlin CS7860 points as recommended by Duke Williams; therefore, I assume that the contacts don't need to be cleaned." New points don't need to be cleaned unless somehow contaminated by poor handling.

**Stephen B.** · June 26, 2020, 06:20 AM

Re: Ignition problem on 70 Corvette 350/350

The key in the "ON" position, my multitester is set for DC volts, the positive lead is connected to the positive side of the coil and the negative lead is connected to a convenient ground, the multitester reads a little over 12 volts.

I checked ground from the breaker plate to the negative side of the distributor. The meter reads between 0.0 to 0.1 ohms; therefore, I concluded that the distributor is adequately grounded.

I cleaned the points and set at .017"; however, the multitester read 0.0 ohms between the distributor coil lead and ground. I adjusted the points to be closer until I began to have a reading the ohmmeter (0.0 to 0.1 ohms).

I set my multitester to DC volts, the positive lead was connected to the positive terminal of the coil and the negative lead was connected to the negative terminal of the coil (the distributor wire was also connected to the coil). When the distributor points made contact, the multitester read only 6.5 volts. Why doesn't it read 12 volts since I have a good ground from the distributor lead to ground?

The ignition timing appeared to be close when checked again; however, the engine did not even try to start.

Thanks again for everyone's help.

**Mark E.** · June 26, 2020, 08:34 AM

Re: Ignition problem on 70 Corvette 350/350

What symptoms? Does it start and run? Crank but not start?

Check the wiring to the coil's + terminal. With the ignition ON it should have 8 - 9.5 V (assuming a fully charged battery and a stock, non-TI ignition) because this circuit goes through a ballast resistance wire. This resistance wire has textured white insulation with blue and red speckles. Is this what your coil is connected to?

I'm not clear what "negative side of the distributor" means. There should be continuity between the breaker plate and distributor housing. If not, the ground wire (hidden under the breaker plate) may be broken or loose.

When checking continuity between the coil's - lead and ground, first disconnect the lead from the coil. It should be open with the points open and grounded with the points closed.

Assuming the car does not start (does it?), I would a) ensure the proper resistance wire is attached to the coil + terminal; b) install new points and condenser (the current ones may be fried because of the the excessive voltage). If the engine ran a long time with full battery voltage to the coil, it's possible the coil is also fried.

Be sure to properly attach the two leads to the points. The open end of each terminal should point down so the wires are up and away from the breaker plate (the condenser's lead in your photo is upside down and dangerously close to the breaker plate).

**Duke W.** · June 26, 2020, 08:35 AM

Re: Ignition problem on 70 Corvette 350/350

The ignition circuit consists of two resistances - the coil primary winding and ballast. Both are similar value, so once the points close and current flows the voltage drop across each will be about the same, equal to about half the applied voltage.

V1 = V applied R1/(R1 + R2), V2 V applied = R2(R1 + R2)

Point gap can be difficult to set because the rubbing block has to be right on the tip of the cam lobe. Bump the engine enough that you can manually rotate the main shaft to get the rubbing block up on the cam and over the top. Then adjust the points with the rubbing block on the tip of the cam. Once the engine starts use a dwell meter to set dwell to spec then set timing.

Wiggle the black wire from the coil to distributor while checking continuity. Also, the breaker plate ground wire will eventually break, but you can't see the damage until you disassemble the dist. Most distributors are in dire need of a blueprint/overhaul, which is easy to do if the shaft bushings are okay, and any competent machine shop should be able to install new ones and hone to size. The distributor is the most overlooked component on the engine, but the engine will not achieve peak output and fuel economy unless the distributor is properly set up including a proper spark advance map for the engine configuration and most were way less than optimum when they left the plant.

I documented the procedure in threads started by me both here and on the CF back in Dec. 2012

Duke

**Larry M.** · June 26, 2020, 09:08 AM

Re: Ignition problem on 70 Corvette 350/350

When you put your multimeter on the coil (-) negative post with the key ON, you should read 12 volts if the points are OPEN. If the points are CLOSED, you will read about 9 volts.

I think your problem is you may have a constant ground from the points to the breaker plate ground. When you set the points at 0.017 inch gap (on high point of distributor cam), and the points are open, you should have very high/infinite resistance between between the coil (-) and distributor or engine ground............not zero (0) ohms. But to eliminate any interference from backfeeding thru the coil, I would temporarily remove the coil to distributor black wire from the coil, and measure my OHMS reading from this lead to distributor ground.

Do you have a dwell meter?? If so, you can connect it to the coil (-) terminal and a ground, and crank the engine over. It will read dwell. You should try and adjust points to 29 degrees dwell.

If you do not have a dwell meter, connect a 12 volt test light from the coil (-) terminal to the distributor or engine ground, and turn the car over with the starter. Black wire from coil to distributor hooked up as normal. Test light should blink on and off. If it does not, the distributor will never fire the coil........and the points are either not working properly or you have a constant ground from the points.

I assume that you DID NOT readjust the points and condenser wires as I mentioned earlier?? If not, why?? This may well be your issue.

Larry

**Stephen B.** · July 24, 2020, 06:48 AM

Re: Ignition problem on 70 Corvette 350/350

I thought I'd give everyone an update on my progress.

1. Larry, I checked the resistance from negative distributor wire to the points, then to the distributor plate and onto the intake manifold. In summary, the total resistance was .1 ohms. I also reversed the distributor condenser wiring for proper installation. Still, the engine would not start.

2. I checked the engine wiring relating to the wire from the starter and the resistance wiring from the key. The resistance wire was not hooked up to the distributor and has 0 volts when the key is in the ON position. The positive side of the coil has one wire that read approximately 12 volts when the key was ON and dropped to 6.5 volts when cranking. I measured the resistance of this wire to the alternator ground with the key OFF (4.0 ohms) and with the KEY on (2.3 ohms). I found a wire splice in the harness that I'm not sure if its factory of a later upgrade. The wires were frayed (see picture). I repaired the splice, and the resistance decreased (I don't remember as to how much is decreased).

My plan is to investigate the current configuration of the wiring and return to stock; however, I have not been able to find where to purchase a resistance wire. For example, Lectric Limited will not sell separate from a harness.

3. I was able to coax the engine to start with a little ether, and it ran smoother than ever. I fine tuned the dwell and timing. When running, the positive side of the coil has a voltage drop of 11.50 volts at idle and over 12 volt with additional RPM's.

4. Future plans are as follow: 1. investigate non-stock ignition wiring configuration as discussed supra; 2. upgrade the spark plug ends on the replacement, dated spark plug wires (I found an article on some NCRS chapter site regarding this to rectify the wires' shortcomings); 3. check the rocker arm adjustment per Duke Williams' article, and; 4. convert the vacuum advance to full time as recommended by Duke.

Comments, discussion and suggestions are welcome.

Stephen H. "Bunky" Byrd

IMG_20200628_081022 (1).jpg

**Jeffrey S.** · July 24, 2020, 10:27 AM

Re: Ignition problem on 70 Corvette 350/350

Stephan,
That "splice" looks like the fusible link that is factory original (the rubber insulators are not aftermarket). Replacements are commonly purchased at NAPA, etc. I think a bit of Google searching should locate resistance wire.
Jeff

**Mark E.** · July 24, 2020, 11:29 AM

Re: Ignition problem on 70 Corvette 350/350

The melted wire is the fusible link for the battery gauge (aka "ammeter", although it's not a true ammeter). You may have had a short in the circuit between the horn relay, gauge and starter solenoid (that's where the red and black wires go). This circuit also has fusible links near the horn relay and near the "B" solenoid terminal. Check to see if they are fried too.

Voltage is too high at the coil + terminal with the ignition on. I wonder if the resistance wire is faulty or has been bypassed. I'd avoid running the car for any length of time with this much voltage to the coil. It may damage the primary side of the ignition and the coil.