More timing advance for points to electronic conversion?

[tgrayretaf]

There's a long story behind this, but to keep it short for now ... I have a 78 that originally had a dual-points ignition set up that I converted to Pertronix many years ago, and it ran fine with "by ear" timing. It took a while to dial it in, but it ran great. I never knew what the timing advance actually was because I never put a light on it. Fast forward ... I had to replace cams (in the process I managed to smoke my Pertronix module) and decided to install a stock-style electronic distributor set up. Timing it with a light, I found that it wouldn't run worth a crap at 0 - 10 BTDC. Right now it runs beautifully at what looks to be around 15-18 degrees advance. Has anyone else experienced a need to advance timing after an electronic conversion? I've seen some vague mentions about needing to add advance to the timing, but no details. For reference, this car has stock-grind cams, the original 32ADFA carb, smog equipment deleted, and a 4-2-1 non catalytic exhaust. Any input would be appreciated.

[18Fiatsandcounting]

The static ignition timing (at idle speeds) should be the same whether the car has electronic ignition or points. The only difference between the two is how the power to the coil is interrupted to provide the spark. Electronic ignition switches a transistor on and off (triggered by the pickup coil in the distributor) whereas mechanical points open and close based on a lever that rides on the distributor shaft lobes.

A couple things could be going on:
1. The timing marks on the timing belt cover are notoriously imprecise, and you have to look at them (and the mark on the crankshaft pulley) at exactly the right angle to determine the timing. Sometimes the timing belt cover is shifted out of place leading to inaccurate timing.

2. Your centrifugal advance mechanism could be sticking. Once you start revving the engine off of idle, the timing should advance all the way up to maximum of around 36 degrees BTDC at 3500 to 4000 rpm or so. If your centrifugal advance mechanism is sticking, the timing might not be advancing as much as it should, and this would make the engine drive like crap. This is easy to test: just rev the engine with the timing light connected, and you should see the crankshaft pulley timing mark smoothly advance above the 10 degree mark on the timing cover. Just estimate how far it advances based on how far the distance is from 0 to 10 degrees and do a mental extrapolation.

If the car runs well at 15 to 18 degrees static timing, then that's where I would leave it. As long as you're not experiencing engine knock at any combination of rpms or load.

-Bryan

[tgrayretaf]

Bryan, thanks for the input. I can't really know what the advance weights are doing when the car is running, but when testing them with the cap off they seem to move freely. With that said, this aftermarket distributor is not the best quality. I had to make some tweaks just to get it to be usable, so who knows what the weight springs are calibrated to. It's hard to judge very accurately how much advance I'm getting as it revs to 3K RPM. And you are absolutely right about the timing marks ... I've worked on classic cars for 40 years and trying to use the timing marks on this Fiat is "getting it close" at best. I enjoyed driving it for over 10 years in blessed ignorance of how it was timed, so I guess that as long as it's running as well as it is, I'm going to keep enjoying driving it without getting bogged down by the numbers.

[tgrayretaf]

Quick update to this. I found an OEM electronic-ignition distributor from a 1979 model on eBay. After replacing the vacuum advance canister and oil seal, I installed it and was able to get the ignition timing down to ~ 0 - 5 degrees BTDC at idle (based on the timing marks on the plastic cover), and get the car to run great. So, If you experience something similar, I recommend start troubleshooting with the aftermarket distributor.