Worn Distributor Bearing causing slow return to idle?
 

I just installed a Pertronix on my '74 fitted with Webers. Set the timing to 35 degree advance at 6000rpm (but it actually stabilizes around 4500).

Had some problems with the engine dying on acceleration prior to the Pertronix install, which went away after. Figure I had bad points.

Now with the Pertronix the engine doesn't die but it is very slow to return to a normal idle. It will drop to about 1500rpm and very slowly drop from there.

I balanced the carbs and set the mixture. Replaced one of the throttle links to make sure everything there is ok. Left the idle setting a little high (~900rpm) while fiddling with it.

Checked the vacuum line to the distributor and at the carbs and all seems ok.

A mechanic friend of mine suggested that my distributor bearings may be worn, causing the gap between the magnet and pickup on the Pertronix to vary. He thinks this could cause the idle problem.

Does this make sense? Any other thoughts? How would I check for this (or maybe I should just go back to points?)

Thanks in advance!

sure on the fuel mixture/progression circuit? are you using a wideband? vac leaks at manifolds? I have no experience with webers on a flat six engine, but have dealt with some similar problems with DCOE's. usually found a vac leak. even a small nick or damage to a gasket can cause problems with causing the engine to come down slowly. I even had to have a manifold decked back to true. awful. .....or that the idle jetting/tuning was incorrect.

The engine did not exhibit this behavior before the change in the ignition system? what other changes besides the ignition occurred? always hard to chase and diagnose when so many variables changed.

I'm just an amateur, but thats some of the stuff I've dealt with. good luck...

Thank you. Only change was replacing the points with a Pertronix. The engine cut-out problem stopped but the return to idle problem started. All the fiddling with the carbs was my attempt to fix the idle issue.

Think I may buy a new set of points and put those in to see if its the Pertronix module or related to the install.

Your vacuum leak comments are well taken, I will check again.

good luck man. I've beat my head on the wall a few times w/ carbs. The juice is always worth the squeeze in the end!

Sticky advance weights in the distributor can also cause the idle to return slowly. Since you just changed something in the distributor, and re-timed it, that's where I would look first.

The new Petronix is showing up the old state of your dizzy. Is this a cleaned unit first and foremost? Many threads on this, and I was AMAZED at the crap inside the dist. body ('78 SC). An easy and very worthwhile task is to strip and clean this item.

worn distributor bushings will cause the rotor to hog out the distributor cap, causing the car to lose spark.

binding distributor internals or the old, tired distributor advance weight springs can't pull the weights back all the way, keeping the idle timing advanced a bit.

Thanks, that is definitely not happening. Good to be able to eliminate the bearings as a root cause!

I will take the distributor apart and check the weights are moving freely. Looking at some other threads as suggested, it does seem to be pointing in that direction.