What should the voltage at the coil read on a stock 71 250 - 360.

Thanks

Robert P.

 

The coil primary resistance is spec'd at 1.4 - 1.54 ohms and the resistance wire at 1.3 - 1.4 ohms. Using the mean of the spec's and the voltage divider rule, here's what I figure:

system voltage / coil voltage

12V / 6.26V

13V / 6.78V

14V / 7.30V

15V / 7.82V

16V / 8.34V

 

I just checked my last week. It had 12v at the coil positive wire.

I assumed it had a drop resistor in it, hooked up a Blaster coil and burnt it up in a few short times of driving it. Bummer, guess I SHOULD have checked it. Another $30 down the drain.

(maybe THIS time I will add the ballast resistor that is SUPPLIED with the kit )

 

I went to change out my points. Put it all back together and now I don't have any fire out of my coil.
I installed a brand new coil. Checked voltage with key on - 11.89 volts. Turned key to start and had - 10.87 volts while motor was spinning. While doing this I had the coil wire disc. from the cap and layed over a bracket with about an 1/8" gap from the metal bracket to test spark; and nothing, no spark at all.
All wires are connected in the dist. The lead wire from the key is at the "+" and the "-" is going to the points. The points are grounded with it's wire. I am wondering if the condenser might have something to do with it? If so what?

Thanks for your thoughts,

Robert P.

 

As long as the points are opening and closing like they should be, close to the right gap of .017,or .021 It sounds like you found the problem. Just make sure your wire from coil to dist. points is good and not broken.
orich

 

A bad condensor will make it not run. Been there.....on the side of the road to boot.

If the condensor happens to be faulty, it will ground itself out, in turn bypassing your points. NO fire!

Try unhooking the condensor and trying it. It may not run great, but it will let you know if that's the problem.

 

Tried it. Still didn't get any thing. I had 12 volts at the points contact, but was not getting it to jump. Mind you this was the "spare" set I had for that emergency. Needless to say they where bad. Put a brand new set on and wahlah.
Thanks for the quick responses.

Robert P.

 

Great! Glad you got it worked out.

So it sounds like the other set of points were not grounding when closed. 12 volts at the point contact when they're open sounds right, there are no voltage drops across the resistor wire and coil when the ground is open.

 

Just for future reference, a quick way to check coil and points in a jiffy is to use a good old fasioned test light. Just put your clip to ground as you normally would, and probe the negative (-or points) side of the coil. Good idea to yank the dis. cap first. With the key on, you should be able to rotate the rotor slightly by hand against the mechanical advance to open and close the points. If you can't turn the rotor enough to actuate the points, you can rotate the engine slightly by hand to put everything in a position where the points are closed. Basically what should happen is that when the points are open, the light should light, indicating that voltage is making it all the way through the coil. When the points are closed, the become the point of least resistance and basically short the light out(light goes off). If your light stays on no matter whether points are open are closed, your coil is good and points aren't making contact. Either clean or replace points. If light never comes on, yet it comes on when probing the positive side of the coil, you have one of a few problems.. Either bad coil, preventing voltage from getting all the way through, or the negative lead is shorted to ground somewhere in between the coil and the points. To test for bad coil, disconnect negative lead at coil, and again probe the negative coil terminal with nothing connected. If coil is good, light will come on. In which case there's a short to ground.. This could be as the lead passes through the side of the distributer, a shorted condenser a was mentioned by freightrain, or even a faulty set of "grounded" points. Also, a condenser can go bad without shorting. The reason for the condenser is to absorb the excess voltage created in the primary by the collapsing magnetic field in the coil when the points opened. If not for the condenser, this voltage spike would jump the point gap as they opened and not only drastically shorten the life of your points, but drastically reduce the available power on the secondary side of the coil. I wished I still had the old book that explained it so well, but there's actually a good way to tell the condition or even the proper sizing of your condenser, just by observing the contacts on a used set of points.. A can't remember which way it goes, but the rule was that if contact metal was being transferred from one contact to the other, and which contact was giving up the metal would tell you if your condenser was too large or too small. Ideally you want both contacts to wear the same. Anyway.. I'll stop rambling for now, except to say that I found it to be pretty easy to convert a factory points dis. to a factory electronic.. I used to love my points.. cuz they were so easy to service on the side of the road... Then I tried a points triggered mallory Hi-fire.. Works great except because the points never arc, so the contacts never really need cleaning and they don't wear.. Unfortunately, the little plastic rub block that actuates the points off the cam DOES wear.. And makes for some extremely funny problems.. How it happens is that you manage to start your ride one day and drive it to the local car show running fine (cuz the cam is smacking the rub block hard enough to knock the points open) Then you go to fire up your fine ride only to find it won't start cuz the engine won't turn fast enough to knock the points open with just the starter. Then you have all these people under your hood with you to help you discover that your points won't open, and then they tell you how to adjust a set, all the time not knowing that real culprit was the worn rub block cuz you haven't looked at the points in 2 years.. This thing actually happens..... OK.. Hope a gave somebody a laugh and maybe a little information to keep in the back of their minds

 

psonnier , thanks for the tip. And as for "and maybe a little information to keep in the back of their minds". I'm going to copy it to my troubleshooting book for the future.

Thanks again, knowledge is always welcome.

Robert P.

 

psonnier, thanks for the informative post.

That saying for the condensor went something like "minus metal on the minus point (stationary point) means minus capacity (you need more capacitance)"