I’ve faced a recurring issue with the ignition system on my 1949 Olds 88. Car starts and runs great, idles at the factory spec (between 500-550 RPM) when up to temp. But as a day of driving goes on, things begin to go bad. The car doesn’t have the pep it did, it begins to backfire, and eventually it’s barely running at all. When I get it back to my garage, I find that the timing is once again off mark.
before I knew what was going on (timing issue) I replaced the distributor, the cap, the rotor, switched from points to pertronix, new carbon trace wires, new plugs.
i know what you may be thinking, “buddy, those aren’t the problem! The problem is the distributor is coming loose and causing your timing to change”. You’d be RIGHT! But it’s not budging. I’ve tightened down the main bolt holding the distributor plate at “zero”, and I’ve tightened up the two small screws that attach the distributor to the plate. Things can’t get any tighter! Still, over time, the timing changes. I don’t think the distributor is moving. What am I missing? I’ve tried to adjust the timing when the engine is cold AND when it’s plenty hot.
My theory? It has to do with the carburetor. Everyone knows timing is affected by RPM (throttle). But what’s odd is that my RPMs return to apx 500, but the timing changes almost every time AFTER I stab the throttle. As I accelerate, but gently return the throttle to no pressure, the timing stays put when the car returns to idle. But If I accelerate and then simply take my foot off the throttle, letting is “spring” back to idle speed, the timing is permanently affected until I accelerate again.
It’s like I have some accelerator pump issue

 

My first thought was varnish in the distributor shaft, causing the mechanical advance to stick, but you replaced the distributor. New, rebuilt, used?

 

I had the original (early 1949) rebuilt by North Star Auro Electric in New York. Then, when it didn’t fix the problem, I bought a rebuilt (late 1949-50) distributor from Fusic. I can’t imagine it’s a distributor problem since I’ve used two separate units. Again, it runs perfect for a while, but eventually, using the throttle ends up moving the timing marks out of spec, even when idle returns to apx 500rpm

 

Distributor weights are sticking, the distributor drive or driven gear is wearing or the point gap is changing...can't think of anything else that would change timing.

​​​​​​Is the balancer outer ring mounted in rubber? Wondering if the balancer is slipping making it look as though the timing is changing and something else e.g., carburetion is the problem.

Is the distributor cap secure? Is the rotor possibly slipping around the shaft?

Good luck!!!

 

Second thought, taking all you've described, is it possible the balancer is shifting on the rubber insert? I don't know when they started using two piece harmonic balancers with a rubber insert, but I have seen the outer hub shift relative to the inner.

 

Mark your vibration dampener with a couple of white lined and see if it is drifting (moving inside the rubber lamination) If you haven't rebuilt the damper it's about time for it to go bad...... Just a thought...Tedd

 

I had the harmonic balancer off a couple months ago. I can confirm it’s in excellent condition. It’s definitely a timing issue. Spot on, then suddenly sluggish, backfire under rapid acceleration, then back to normal.
ive been playing with throttle linkage today. Making it tighter to ensure the throttle is closing properly. I also took apart the carb again today. I rebuilt it completely this winter. All looked good.
im currently running a pertronix electronic ignition. I can confirm it’s the correct unit for my 6v. It was bench tested at North Star many times. I’ve been told the distributor has a very smooth curve with no issues. I trust their work. It’s a head scratcher for sure. I’m going to put the points back in and see if the issue is the electronic ignition. I don’t see how it can be since the change in RPM causes the issue, then it returns to normal when I mess with rpm. But who knows

 

I wonder if I’m having an issue with the vacuum advance. I trust it’s in good condition, after all, it’s a remanufactured part that was examined and tested by North Star electric. Again, I trust their work. But I wonder if I’m misunderstanding how it works on my car. Here’s a quote from the service manual:


Sounds like it’s only supposed to have an affect at higher rpm. I wonder about plugging the vacuum advance when I set initial timing… shouldn’t work, but who knows. Perhaps I should

 

You should always disconnect & plug the vacuum advance when establishing initial timing. If not, you’ll introduce advanced timing at idle which is not what you want to do. Since you previously had stated you set the timing (in an earlier post), I assumed you knew this. Initial timing is set with vacuum advance disconnected and plugged.

 

To check the vacuum advance unplug the the vacuum hose and by mouth suck on the hose and see if it will hold a vacuum( your tongue as a valve).If the diaphragm is bad it won't hold a vacuum....Tedd

 

Thanks for the encouragement and help everyone. Norm, you hit the nail on the head! It's interesting to note that the factory service manual didn't mention the need to disconnect the vacuum advance on the distributor. Maybe that's just "common sense", but I didn't know about it. It made all the difference. Here's what I did that WORKED:
1- begin with new points/condenser inside distributor or ensure they are adjusted to specification.
2-disconnect the distributor vacuum advance from the base of the carb/engine.
3- plug the now open vacuum port on the carb/engine. Failing to do so will affect engine RPM.
4- start engine and allow it to warm up to normal operating temperature.
5- with automatic transmission in neutral, adjust engine RPM to 500 (factory manual states 500 RPM is the ideal idle speed).
6- loosen distributor hold down clamp and align distributor timing mark to zero. Tighten bolt into place.
7- loosen adjustment screws that secure distributor to distributor hold down clamp. These screws allow the distributor to be rotated to advance or retard the timing.
8- using a strobe/timing light tester on cylinder 1, adjust timing by rotating the distributor until the engine timing mark points between the two reference ***** on the harmonic balancer. Once aligned, tighten adjustment screws securing distributor to base plate.
9- remove carburator/engine vacuum plug and re-attach vacuum line to the distributor vacuum advance.
10- check engine RPM and adjust to 500 RPM.
Timing procedure should now be complete. At idle, the engine timing mark should point between the two reference ***** on the harmonic balancer. As RPM's increase, the timing will not appear to remain the same using the timing light, but rest assured, the engine is timed properly.

After adjusting the timing this way, it runs strong, accelerates without hesitation or backfire. Let's hope it holds! I'll come back with an update in a couple days. If I missed anything or if anyone more experienced sees a problem with my procedure, please let me know. I love to learn!

 

You got it spot-on. Nice job.

 

It’s been a couple days and a couple hundred miles, and I’m pleased to announce the Olds is running fantastic! I’m averaging 13mpg mixed town and +55mph Highway. I can’t thank all of you enough for the help you’ve given me over the past 6months or so. Pure joy!!!

Fueled up at the only Sinclair I know of in New England. It’s a hike to get to, but you can’t beat the drive!!