[NYBRIAN]

Ok it has been a while since I diagnosed a points based set up so be gentle.

Resistance wire is approx 1.8 ohms res

I have Accell coil 8140?

Had Petronix but 17 volt surge from bad ext regulator fried unit.


I am trying to set up points to use car. All orig wiring is still there just bypassed for Petronix.

My question is res wire cuts volts to approx 6.8 volts with Accell coil and I think 9 volts with stock? I have coil laying around but not sure it is stock 69 GM??

I am thinking Accell coil does not need external resistance wire as cut will protect both coil and points? Enough resistance?

2nd question the yellow wire coming from starter to the coil is supposed to jump 12volts to coil while cranking to help staring. This is where I get lost. Voltage available won't be 12v as at cranking there is 9.5v-10.5 or around there so why did GM bother with this set up??

If it is from 6volts I can understand the jump to say 10.5 volts but if the 9.0 volts at the coil is correct what is the reasoning for the jump from the starter?

Also why not take it from a solenoid of even the start wire itself going to the starter? Wouldn't this avoid voltage drop through starter solenoid?

Sorry for long twisted question just trying to remember and get better operating points set up. Petronix was good but with no way to diagnose their unit I will pass on a new one.

[dale68z]

Don't know what you are trying to diag. but.
You need + volts at + side of coil. The lower the volts the longer the points will last.
The higher the voltage at + side of coil the more energy the coil will have.
There needs to be a happy medium. If you just want to hear the engine run, run batt+ volts at the coil. The points will burn, and need to be cleaned/ adjusted or replaced more often. You could easily drive a car 1000 miles with 12+ volts at the coil (my experience). Dom't sweat the voltage, I would say the coil should have more than 6 volts while running

The points are a ground, which switches on the coil, then opens up, collapsing the field in the coil inducing voltage into the secondary side of the ignition system.

[Everett#2390]

Adding to Dale's explanation, since GM has a resistance wire, the Accel coil can be used as is. Other brands had battery voltage at coil and they used a ballast resistor from Accel. Be prepeared to replace the point set more often with the Accel coil than a stock coil.

Having resistance lowers the available voltage for point contact protection preventing them from burning up sooner than 10K miles when preventative maintenance was followed by the Owner's Manual.

The yellow wire from the solenoid provides battery voltage, typically around 11 volts if battery is good and proper cable gauge is used, and is connected to the R terminal of the solenoid. This terminal is closed when solenioid is engaged during the start. If the yellow wire was connected to the S terminal, along with the purple wire from the START postion of the ign switch, then the yellow wire would provide ign voltage to the solenoid all the time, starter engaged all the time.

[NYBRIAN]

You guys are kind of just restating what I have said?

The idea of lowering the voltage to the coil is not in question. The GM res wire is approx 1.8 . I have no idea the res of a factory coil? With the ACCELL coil with a solid 12.65 volts equates to approx 9.5something volts which should be fine. Other coils only have .32 of res and need the addtl resistance. Each coil has to have the resistance added based on what it's internal resistance already is otherwise you are right juist run the 12v straight and deal with the wear and possible coil damages.

The questions I have are what is the res of a stock GM coil to determine if the Accell needs further res in way of a external resistor? If GM cuts it down to 6v then the addition of the starter circuit of 9.5-10.5 volts make sense and the Accell needs an external res.

The wire coming from the starter terminal can only deliver cranking voltage which is usually 9-10.5 with a good battery. Are you saying you get 11volts at crank?? Also this is with modern batteries. Problem is you read everywhere that this circuit is delivering 12.5 volts and it isn't. Just trying to get some good discussion as to what GM was thinking.

This is a 11.5 compression BBC so I am sure there is addtl strain but again nothing more then cars of that era. I am trying to understand why GM would add the addtl circuit for such little gain.

I understand amps are the way to measure draw and starting set up. Just trying to understand GM's thinking. I couldn't imagine with a tar top battery they had cranking voltage any higher then 9.5 volts???

[Steptoe]

Historically the lower ballist Voltage is a left over from 6V systems andvery cold mornings where batteries did not function well...hence the starter draw sucked to much from a 12 v pionts system turned the engine and not enough juice left to fire the plugs.
I work on old vintage cars with 6 V systems , convert to 12v etc etc
A balast system requires a ballast type coil, which is usually stamped on the bottom with a 6 in the part number ...a 12v coil is usually stamped with a 12
If a 12v coil is used on a ballast sytem, after about 20 mins the engine dies, leavig the driver trying stuff..the suddenly it fires up and runs for another 10 mins and repeats
Also running a 6v coil on a 12 v system will do the same thing
This is a common occurance with ppl putting a ballast based engine in a boat then forgetting to use the ceramic ballast resistor (Aus NZ GM.Ford used ceramic ballist resistors not as in the states a resistance wire.

Now running a balast points system on 12v ....ideally one should change the condessor rating to suit....if burns on the anval side if the pionts lower (from memory the condesor rating) and visa versa if the hammer burns
Also the size and length of the wire from the coil to the pionts can effect how the pionts burn or last.
Using ballast pionts on a 12v system with a 12v hi output coil..yes gives the pionts a shorter life, but not as short in real life as we are lead to believe...instead of say 20K out of a set of pionts expect 10 or 12K .....and adjust the dwell or at lease check every 6 months , not 12 months.

So if u drop 12 v on a pionts dizzy with a 12v coil, u may find on that morning u are snowed in , and the battery because its cold is not efficient, u may have an issue starting
Other than that and a slightly shorter life of pionts that is not significant....u have a good 36 K or even 48K Volt spark and good to go...and thats not even changing the condesor
Personal experiance over 40yrs on my own vintage and boy racer cars back in the day and boats.

[alanrw]

I think the question he is asking is why 12V at crank? Simply put, during crank, GM wanted to increase voltage to the coil temporarily to insure spark plug fire. Once the starter is disengaged, voltage reverts to the lower value which is more than enough to fire the coil off the points.

As to what the correct ohm value is, certainly, 1.3 ohms is pretty insignificant as far as resistance goes in any wire but to answer your question, not sure what the ohm value is of a correct length of coil resistance wire is. But as mentioned above, running a system on 12V all the time will result in a faster burning of the points over time compared to running stock points at the lower voltage as designed by GM engineers.

alan

[Steptoe]

Simply put, during crank, GM wanted to increase voltage to the coil temporarily to insure spark plug fire.

And the historical reason was because of snow and orgibnal 6V systems...

running a system on 12V all the time will result in a faster burning of the points over time compared to running stock points at the lower voltage as designed by GM engineers.

Yes..but it is not signifivcant, as I mention change the consener value and and there is no difference....outside GM outside the US cars built all over the world ran 12v coils and pionts....factory...it could be said US manufactors where well below the ape ball in this area...