Stored the car for the winter( 26th year)For the first time it would not start,good cranking power ,no fire, I changed the points and it fired right up.Set the dwell to 30 degrees and the timing went to previous setting.i have a miss and back fire ,rough idle,My dwell meter is 38 years old,so i checked it with a newer one 25 years old and the reading is the same,The newer one has a points resistance gauge marked good / bad it pegged the needle to the bad side. what does this mean ?
Is this the answer to my missfire?

1970 coupe 350 auto

 

I'd change the points and plugs just because. Then I'd "freshen" the fuel in the tank. If it's a consistent misfire you might have a plug wire come loose or simply bad.

How "fresh" is the carb?

Thinking out loud,..good luck!

 

Plugs are fine,points have about 15 min run time max,wires are 1 year old,cap and rotor 2 years.The car was running the best it had in 25 years when i put it away.The fuel should be ok ,i added stable,4 gallons of race fuel,1 bottle of octane 107 and filled the tank with premium,same as the previous years, The point resistance showing bad has me stumped

 

When you have two pieces of nice shiny clean metal touching each other, there is no resistance and current flows from one side to the other with nothing to stop it. You get maximum current flow when there is no resistance. If the two pieces of metal are "dirty" with a surface layer - an oxide formed by water/rust/etc ... then it turnes out that rust does not conduct electricity as well as metal -steel/copper/etc. I'ts like putting your hand on a teapot compared to wearing a glove and grabbing the teapot. Heat flows through copper just like an electrical current flows through copper - same kinda thing. Each metal has its own current carrying capacity. Copper and aluminum are best. The equation is V = IR. If you have 12V and no resistance (0), then the current is 12/0 = infinity. If the resistance increases from let's say from 0 to 12 ohms, then the circuit can carry only 1 amp. This is the relocating the battery to the trunk problem. With the points scenario, lets say you have some starter circuit resistance, when you crank the starter, current is being sucked out of the battery, the voltage is being pulled down from 12 volts to maybe 9 volts ... and then you are also trying to put current through the points at the same time. But, you may not have 12 volts to start with.
What happens if you have only 9 becuase of the cranking, and you also have some kind of corrosion in the points circuit? Same equation for the points circuit V=IR; resistance increases, voltage is lower to begin with but is considered the same - and current therefore decreases. Right? Resistance increases, voltage stays the same and the current decreasses. Ooops, current decreases! What does that do to you. Well, the current from the points runs into the low voltage circuit in the coil. The coil is made up of 2 coils - low voltage and high voltage. the two coils of wires are next to each other so that the current that runs around the low voltage circuit coil and creates a magnetic flux. the magnetic flux induces a voltage in the high voltage circuit ... see where this is going according to the ratio of high voltage turns to low voltage turns (ACCEL uses more turns, the ratio is higher and the induced voltage is higher ... than a stock coil), then the high voltage is set out to your spark plug. High resistance, low current, low induced voltage all equal WEAK SPARK. Note that the ballast resistor is used to knock down the current level so that you have 5amps running around the wispy thin wire in your coil. If you remove the ballast resistor, the current will increase and you'll get a great but short lived spark.

Your meter indicates corrosion in the points circuit but keep in mind that if your battery connections are bad and your starter is pulling the battery down and the battery is weak to begin with, your ignition circuit won't be working optimally. Current does not flow through oxides as well as it does through copper. Clean all connections - especially the grounds.

 

Your problem most likely is the small black wire going from the rotating points base, moved by the vacuum advance, to the dist frame....main body....i'ts down there about 1/2 hidden, take a flashlight to see it....
rotor button has to be off, two screws, one on each end....
that wire gets tired, it's s special kind of super flexible wire, and I suspect NAPA would still have it...about 2 bux or so should cover it...

 

This points resistance test is being done with the points CLOSED-correct? I have never seen one thats done while the engine is running.Just a thought.

 

Huh???

 

The idea I think Tim_Ko is headed toward is that the resistance test is only as good as the combined total of components you are connecting through. Every connection and electrical part in the test 'circuit' is being measured using whatever power source the meter has as a reference voltage.

 

 

So far have done the following,new,points,condenser,cap ,rotor,fuel,filter,drained fuel tank ,added new,cleaned carb,At idle runs fairly smooth.Under load ,in gear very little throttle vibrates,shakes 10mph its not too bad,
With car at idle i started to remove wires from the cap ,found 3 cylinders not fireing ,that is when i replaced the cap and rotor.The dwell is at 30 and is steady the voltage at the coil with key on is 6.5 volts,I am going to replace the coil on sat morn and the flex wire from dist to coil. the 3 cylinders are in in a row on the cap.All parts purchased so far are Delco parts ,not that they are the best money can buy,they are better than nippen gingo or what ever the discount stores sell.

Thanks for the help so far

 

Did you visually inspect the points, cap and rotor? You can see corrosion on the points, rotor and cap. Cracks in the cap can be a problem - flex it with your hands and see if you hear a crack. You can test the condensor using a multimeter. But, I'd bet those parts are still good ... and its a bad connector on the spark plug wires. I say that because, it seems that the only thing you didn't replace was the wires.

 

The distributor bushings are worn causing the rotor to woble just a small bit ,which caused 3 cylinders not to fire.I changed the distributor(borrowed one)from a friend and it fired right up. I have found out this is a common problem.I am going to have it rebuilt and converted to electronic.
Thanks to all that replied

 

Just something that nobody else has covered here. It is also good to use an OHM meter to check the resistance in the spark plug wires. They may look good but could break down inside.

 

For anyone.....

lars just rebuilt my dizzy. Beautiful. But, it had HEI from before and he took it back to points.

Now I only have one wire coming from the dizzy. Does that go to the NEGATIVE side of the coil????

(I am assuming that is where it should go).

WAYWRONG - any luck getting you started up?

 

Yes, the wire from the distributor goes to the Neg. side of the coil.