My 76 f100 died on me the other day. Tracked it down to a bad coil. Had an old one in the bed swapped it out and it ran fine. So I went to auto store and bought a. Accell super coil. 12 volt universal. After installing it I noticed a power improvement but it backfires horribly through the Carb. Went back to the old one in the bed and the backfire stops but doesn't have the same power output. The manual says 8volt oil filled coil. Is the voltage the problem? Any suggestions would be great before I return the coil. It's either a 360 or 390 motor. Will dowel test the stroke when I can to be sure.

 

That is an odd problem. I have never played around with coils much so I don't know what the deal is with the 8 volts, that just puzzles me since all cars I have ever heard of are either 12 volt or 6 volt systems. Not to say 8 volts is wrong, I just don't know much about coils. As far as backfire with one and not the other, sounds to me like the supermarket coil is either putting out a hotter spark or its getting to the plugs faster. Try playing with the distributor a little to adjust ignition timing and I would imagine that will fix that problem. Hopefully someone smarter than me will help us both learn a little about coils and answer your electrical questions.

 

Ya the Guy at Oreilly told me to retard my timing a little also. So I think I'll mess with that this weekend. Unless someone else has another suggestion. I think my Haynes manual says 8 volt oil filled coil is the specs page. Which seemed odd to me also. I just checked the replacement coils at Oreilly and they all say 12 volt. So I don't. Think that was the issue

 

Thought of another thing. Should I use the external resistor that was on my old coil with the accel coil? I tried both ways. Seemed worse without the resistor

 

i agree with the guy at O'Reilly's- try retarding the timing a bit.

as for 6v/8v/12v coils....the old-school stock coils can't handle 12v all the time- they'll burn out. to prevent this, Ford used a resistor wire (pink) between the key switch and the coil to knock the voltage down from 12v to 7 or 8.

aftermarket coils can generally handle 12v all the time. (double-check yours to make sure.) if so, then to get the most out of it, you now need to bypass that resistor wire. follow the instructions that came with the coil, it'll probably have all this in good detail, including what to do with your external (ballast) resistor.

 

Ok, that makes sense. The old one he had was an 8 volt that requires the resistor wire and the new accell super coil is a 12 volt capable so it pumps out more juice to the plugs resulting in a quicker and more complete fuel burn which is starting while the intake valves are still closing and shooting fire up the intake. Bypassing the resister wire will result in even better burn which is good for power but creates more back fire without adjustment. Retarding the ignition timing by turning distributor counter clockwise will delay the spark a little and thus let the intake valves close completely before the cylinder fires. Makes sense to me I love learning new stuff.

 

almost forgot- you may also be able to gap your plugs a little wider to take advantage of the hotter spark.

 

Thanks for the info. The ccoil has hardly any instructions. I'll just make sure I get 12 v to the coil. Eliminate the resistor and dial in the timing and se how it goes from there

 

Did you get the Accel 140001 to replace the Duraspark coil?? If so, the Accel coil has a lower primary resistance than the Duraspark coil... so you should also use the Accel ballast resistor (.83 ohm) in place of the Fords 1.2 ohm resister.

With ignition on & engine not running, you should have 6~8 volts at the +coil connection. You probably have less than 5 volts using the original resister. If you run straight 12v to the coil, you risk burning up the duraspark module.

Also, don't just GUESS at your timing... check it using a timing light! If you still have trouble with backfiring after all of this, I'd replace the duraspark module (they're fairly cheap). What ever killed the coil could have damaged the the module too.

Let us know what you find out..

 

%^@%@@%@!!!
i completely missed that he's running a 76, which would have the Duraspark setup. all my stuff is older, pre-Duraspark.

forget what i said- just get a OEM-style coil and don't worry about it.

jmf66- thanks for catching that.

 

Its the accel super stock universal coil. P# 8140C

 

And I believe I had about 8 volts when I was checking it out when I determined the coil was bad

 

Ok got home and started looking again. Put the coil in. My vacuum advance on the distributor has 2 ports. They were just jumped to each other. I need to get them tied in. Where do they need to connect? All I can see in my manual only shows one port. I need to get all my vacuum lines set up and go from there. Any help would be great

 

I have never dealt with a distributor with 2 vacuum advance units, but I know the distributors with one vacuum advance, the hose runs to manifold vacuum port on the bottom of the carb. On my autolite 4100 the port was on the back and was tapped. A piece of flared steel tubing with a brass fitting on it ran around to the front where a rubber vacuum line connected and ran to the distributor. On the holley 4160 I have now the port is on the passenger side of the primary fuel block and the rubber vacuum line just plugs onto the barbed fitting on the carb. I don't recall where it goesbon the edelbrocks or the motorcraft 4200, and I have never had a 2 barrel.

 

Okay I think I figured out my vacuum tubing and advance hookup. Got a coil and external resistor. Mine was missing. Where does the resistor hook up? The way the auto parts Guy told me didn't work. It wouldn't even start that way