I have a 71 cutlass conv. mildly rebuilt 350.
This year it started to stumble or miss under 2k rpm.
over that it runs great, It does not do it in park just when driving and worse
under a load. I have three differnt carbs and tried them all.. Same problem.
Changed the cap and rotor, and mecanical weights. It has a pertronics
kit for the distibutor. new wires , new plugs. also does it with or with out the vacumm hooked up.
Im lost now. any ideas would be great.

 

Grab a voltmeter and test to see how much voltage you have at the coil with the ignition on (motor not running).

- Leave wires connect to coil
- Use jumper wire and connect the negative side of coil to a good ground in the engine compartment
- Connect voltmeter red wire to + side of coil and the voltmeter black wire to engine ground




You should be pulling around 11 volts with the ignition on. In my case I was only pulling 5 volts and because I did not have the ignition source wire hooked to the coil correctly. The Pertronix installation instructions are not very clear and I wound up installing only the wire to the coil that allows the car to start and not a power source after the car was already running.

I had the same symptoms you talk of at low speed/rpm. It always felt like a carb adjustment issue so I rebuilt the carb and adjusted it at least 10 times. Turns out I was barking up the wrong tree.

Anyway, try this and see if the Pertronix module is getting enough juice to allow it to work correctly.

d1

 

Thanks for the info. I tried it and had 12 volts. The ground wire was a little loose, so i tightend it up. but i still has the miss. might try the coil next even though it only has about 500 miles on it