Simpl question for the right person------maybe

H

harryc

Senior Member
I run a regular model A distributor with modern points and condenser and 12 volts. I decided I would try a high performance coil out of curiosity. I know little of automotive electronics. When I connected the new coil my car stumbled and would hardly run. I put the old coil back on and it ran fine. I tried another time making absolutely sure everything was connected properly and had the same result. So now I am back to the older coil with my car running fine. I don't get it . Switching the coil should be simple! Could the condenser have anything to do with it? Any suggestions?
 
Maybe a little more info... which "High Performance" coil? What's the ohm rating?

I'm running a 40611 Pertronix Flame-Thrower 3 ohm coil with no problems.
 
harryc - if you added a higher output voltage coil, you may want to check and be sure the spark is not arcing to ground or to another cylinder.
 
I would say that 9 out of 10 new 12v coils will be needing an external ballast resistor for use with points.

This should look similar to this one;

 

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the opposite could also be the case. Maybe he has a resistor with his old coil and the new coil doesn't require one. Then you wouldn't have enough voltage to run the new coil.
 
A new 'high performance' coil is not going improve anything as long as everything is as it should be.

The fellas covered it, points should only have 6-8 volts feeding them requiring a resistor somewhere, either outside of the coil or internal. Ohm reading will tell or the coil should have it printed on it maybe.

Also the new coil could oil filled. They do not like to be tipped upside down. You could try pointing the connections skyward and see if that helps.
 
my old coil was a standard coil for a 1968 mustang. It used an external resistor. My new coil was a petronix 1.5 ohm which does not require an external resistor. Everything was connected correctly--honest. The reason for wanting to switch was to see if I could get my plugs to burn a little cleaner. My problem may be because I require a coil with 3.0 ohm rating-not really sure
 
are you sure your battery is fully charged older stuff can sometimes run on lower voltage where something high performance may take more juice to operate properly.
 
Put a resistor on your coil. 1.5 ohms is not enough resistance for the primary side of your ignition system. The primary current will go up and You will burn the points.

As Al in NY stated, you may now have way too much voltage to the plugs that something may be arcing to ground.

Even modified Model A Fords do not require extremely high voltage to the plugs.

My opinion,

Chris W.
 
I'll bet you're right. When I bought the coil I was told no resistor was needed so that was how I connected it. I just looked over the info that came with the coil and it says a resistor is needed for a 4cyl application. I'll find out tomorrow.
 
Being a 4 cylinder won't matter for the coil and resistor. Using 12 volts on a 1 1/2 ohm coil instead of 6 volts is what does matter, and makes the resistor necessary.
 
today I put the new 1.5 ohm petronix on the A using a resistor as suggested ( even though instructions that came with it said no resistor needed). It ran great and idles smoother than with the old coil
 
harryc said:
today I put the new 1.5 ohm petronix on the A using a resistor as suggested ( even though instructions that came with it said no resistor needed). It ran great and idles smoother than with the old coil
Click to expand...

Harry, 1.5 ohms isn't enough for 12v. The 1.5 is for 6v. You need the Pertronix coil that I mentioned way back in in post #2... :p:p
 
You are right . The petronix webpage indicates that but the info included with the 1.5 ohm coil doesn't. The 1.5 does work great with a resistor however. Actually I already have a 3.0 on order so I won't need a resistor---thanks
 
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