Ignition system voltages...

My engine has been breaking up above 4200 rpm with both a pertronix and standard points under the cap on the prestolite dual point distributor.

Looking at the electrical system and here are the voltages:

Alt 13.47
Pos @ ballast resistor 11.82
neg @ ballast resistor 8.26
pos @ coil 8.26

I am using an Accel 8140 coil. Does the setup with the pertronix Ignitor still require the ballast resistor?

How do the voltage readings look?

Thanks

I'm assuming the plugs/plug wires are good. I would check rotor phasing. If it misses at the same RPM AND the same load (in hg vacuum) in all gears as opposed to just 3rd gear then yes that would point to ign rather than fuel starvation

Firecore 50s on there and it will misfire in neutral revving it in the driveway and on the road.

Voltages look ok?

I believe with Pertronix you toss the ballast. But I think that depends on what coil you have. The Pertronix itself wants full 12V but if using a regular (non Pertronix) coil I think you would need to keep the ballast to reduce the voltage to the coil but not reducing it to the Pertronix. Not sure on that so I would check further (never ran Pertronix). If the Pertronix does not have full 12V I would jump 12V directly from the alt to it & see if it straightens out then 12V directly to the coil & see if it straightens out for a quick driveway test to see if that was the culprit. As you know you wouldn't want to keep full 12V on a regular coil for an extended period of time. You do have an excessive voltage drop from the alt to the ballast, over 1.5 volts. I would clean connections to deal with that. Holler back how it goes.

The Accel 8140 coil is a relatively high resistance coil (1.4 Ohms). Means that it doesn't have very high energy to the spark plugs...
It also means that with a ballast resistor you have even less available for the spark...

As far as I know the Pertronix 2 & 3 are internally limiting the current to avoid burning the coils, and you are not supposed to use any ballast resistor with these. I use the Pertronix 3 without a ballast resistor with the FlameThrower 3 coil, which is a high energy/high current coil (current draw is almost 4.5 times the Accel 8140 coil...). Never a problem.

I have the Ignitor. Coil specs were very close on the pertronix flamethrower v the 8140.

Would you suggest bypassing the resistor?

Quote:

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I have the Ignitor. Coil specs were very close on the pertronix flamethrower v the 8140.

Would you suggest bypassing the resistor?

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If you mean you have the 1st generation Pertronix Ignitor then I believe you need to use a ballast resistor. This generation Pertronix doesn't have built-in current limiting from what I have read.
- If this is the case it might be a good idea to upgrade to Ignitor 2 or 3 with the corresponding suitable Pertronix coil.

- If you don't want to upgrade you could try with a lower resistance ballast resistor. This will load the Ignitor more (bigger current) so there is a certain risk you fry the Ignitor output transistor. Your coil seems not to be fully loaded so probably less risk that you fry the coil.

The FlameThrower III (generation 3) coil is far more powerful than the Accel 8140 coil. The old Pertronix coils may be more similar to the Accel 8140, that's something I haven't checked.