So I had a broken distibutor and I got a new one from Autozone. Installed it with the new points it came with and it ran great. I decided to upgrade to a Petronix Ignitor III ignition and now it idles like crap but runs great otherwise. throttle response is fantastic. There is clearly something wrong as I can see the tachometer needle drop almost to zero intermittently. I ran a jumper wire from the battery to the coil + and it made no difference. Ground cable from block to firewall is new also added a ground cable from alternator to battery. I need advice please!!

Chet

 

Have you checked the ignition timing after installing the PerTronix?

 

Yes sir, I set the timing to about 10 degrees and runs real smooth but this intermittent rpm drop is troubling. I also noticed now that my timing light is not flashing like it should. Hardly at all.

 

My guess is the gap between the pickup & stator (or whatever the pertronics is using)

check the vacuum advance plate to see if it is loose. I have seen many rebuilt distributors that had very sloppy advance plates. You could check this by disconnecting the vacuum hose, since the plate would not move when throttle is raised. It would now run bad at all throttle speeds.

 

I was under the impression that the gap is not adjustable as it comes with a flat head machine screw but that only locks one side of the plate. I'll check if its concentric tomorrow. I checked the vacuum advance with my mity vac and it was working nice, but I wasn't looking for loose a loose advance plate. Thanks

 

Also...I was just reading up on the pertronics.... an older timing light may not work with it since its a multi-spark. That wont affect what you are doing... just a thought.

 

Not sure about later versions or for your particular distributor, but the gap is .030 on earlier versions simply because the pickup needs some nominal extra clearance to allow for slop or wobble in the dizzy shaft. In other words the gap should not really matter so long as it is close enough to reliably fire. If you can move it closer any (without hitting anything) try that, maybe.

Weird symptom. - if idle is poor it usually means trouble everywhere else.

 

Another thought.... Did you replace the coil?

 

My one and only Craftsman light was brand new...... in 1985 Thank you for the info!!

 

Thanks I'll keep that in mind!

 

Sure you're not arcing across the coil (er, cap) towers? That will screw the idle up good. When I upgraded the coil to Flamethrower, deleted resistor wire I had to stuff the boots with silicone to prevent that. Nary a problem now.

 

Yes, I got a new Flamethrower 3 the suggested coil. One thing I have neglected to do was simply measure the voltage input to the coil (no ballast). My alternator is putting out 14 volts though.

You guys have gone way above the call of duty!! I've very grateful.

 

No dielectric grease used....yet. But I love it and generally use it on everything. Are you saying it's arcing across the + - terminals or the high tension side of coil at the distributor cap?

 

Here's something to sleep on.

 

Yep. If you look at the newer higher output distributors the cap is bigger in diameter, partly for this reason - increased voltage with modern ignitions. When I upgraded the coil from stock point coil to a Flamethrower w/ full battery voltage (40k volts) that was when there was some intermittent arcing between plug wires - across the boots at the cap itself. And of course missing and stumbling at idle.

So risking nothing, stuffed each boot and receptacle well with dialectric from Permatex and the problem went away. Depending on how the coil is situated that can have problems too, a big dab in the boot there will do ya.

Checking under the hood at night is good practice to check for this kind of thing, any weakness in insulation or faulty wires, parallel wires can cause problems when going to a high output system. Not saying this is your problem, but it's definitely something to check.