Flickering Generator Idiot Light

[Classics Fan]

I have 1972 LeMans with the T41 GTO appearance package with 52,000 original miles. A couple of days ago I was setting the ignition timing and adjusting the carb idle mixture. Simple enough but strange things started happening. First the starter seemed to have gone bad from several hot start-ups while adjusting timing. When the key was turned to ignition, the starter would engage for a brief second then all battery power was lost. No interior or instrument panel lights, no horn, etc. The only way to restore power was to disconnect then reconnect the cables at the battery. I jumped to the conclusion the starter was hanging up and voltage was interrupted. Long story short, replacing the starter didn’t fix the issue. What I found that DID resolve the problem was replacing a bad battery cable end on the negative terminal. Well, I guess at least I have a new starter to replace the 48 year old OEM part.

While replacing cable cable ends fixed the starting issue, another problem popped up (all stemming from simple timing adjustment!). While idling in Park at 730 RPM, the GEN light in the dash cluster flickers. If I bump the throttle to approximately 900-1000 RPM (by ear) the flickering fades away and stops but it returns when engine speeds returns to normal idle. I have 14.8 volts at the battery with the engine turning at at any RPM so the alternator seems to be functioning as intended without a problem with the voltage regulator. The battery itself measures 12.6 volts. I am not very electrically inclined. Anyone have any ideas where to go from here?

 

[melsg5]

You probably have the original alternator and 730 in park is pretty low causing the alternator to not generate sufficient output.
Are you using a dwell meter before setting the timing?
Are you using a tachometer to adjust the idle speed screw and the idle mixture screws?
Are you disconnecting the vacuum advance to adjust the initial timing?
.

 

[Classics Fan]

Thanks for your response. Yes, original alternator. Converted to HEI so no points. Yes on the other questions. 13* initial (slightly high), 19* mechanical advance and 20* vaccinator advance. Pulls 21” of vacuum at manifold. Definitely think I need to bump up the idle speed. I just wanted to check for thoughts and opinions in case I’m missing something.

 

[Classics Fan]

Vacuum, not vaccinator

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[melsg5]

You are aiming for a total of initial plus mechanical advance of 36 at about 3K rpm. Sounds like you are only at 32.
Did you put lighter advance springs in the distributor and are using a brass advance stop or made sure the nylon factory stop is in good condition?

 

[Classics Fan]

I haven’t touched the distributor. The car was running reasonably well, I just was dialing it in. Now I’m having a hard start problem if I miss “catching” it at the first fire. It took me almost 45 minutes of repeated attempts in a parking lot this AM before it gave a cough through the manifold and carb and blew blue smoke out the PCV valve (interestingly mounted in the manifold not the valve cover like I’m used to). It finally fired the next immediate attempt.

Incidentally the flickering idiot light has been dark all day. Go figure.

There’s always been a cold misfire that persists until the engine is fully warmed up. I don’t know when the plugs and wires were last changed. My plan is to get new ones in and then turn my attention back to timing. I haven’t messed with weights and springs before but understand the basic physics. Time for some YouTube University!

 

[melsg5]

So exactly what HEI distributor did you install? The typical stock initial timing would be 9 BTDC.
Unless this is an aftermarket performance distributor with a performance curve that 13 is high.

 

[melsg5]

When you installed this distributor did you connect a 12 volt source to it. The stock wiring harness has a resistance wire that drops it to 9 volts.

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[Classics Fan]

As I admitted, electric is not my forte. The PO swapped the HEI distributor in. He seemed competent and did clean work. I don’t know but strongly suspect it’s GM since he was a strong ACDelco kinda guy.

9*, huh? I thought it was 10 but believe you. I know 13 is high and a probable contributor to the hard start problem. That, and things like how I’ve now pulled 5 plugs and found them all gapped WAY over the .035 spec for them. Like at least .050.

Really appreciate your input!

 

[melsg5]

You have an HEI so I would set them for .045.
I have a Mallory HiFire in my GTO for a couple of decades and gap my plugs at .045.

 

[Classics Fan]

Yup, you’re right. The misfires are much more pronounced at .035. New wires and plugs coming up. Then move initial to 9* and go from there. I’ll let you know where it all ends up. Thanks for the help.

 

[melsg5]

You are correct on the 10 BTDC

1965-75 Pontiac & Tempest Tune-up Specifications

1965-75 Pontiac & Tempest engine tune-upspecifications including timing, dwell angle, and Spark Plug Gap, and firing order.

www.tpocr.com

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[Classics Fan]

New plugs and wires today yielded nice improvement in cold-start idle and overall smooth power but didn’t fix the hard hot-start. However, with better spark it’s now apparent by the sound that timing is too far advanced, duh. I will dial it back to 10 in the next couple of days. When I do, will mechanical and/or vacuum advance be affected? The logical answer seems to be no.

For kicks I rechecked timing after plugs/wires without retarding initial (13). Mechanical is now 22 and vacuum 23. All-in is 46 at 2350 RPM. Which brings up a question... earlier you said the goal was initial plus mechanical equalling 38 at 3000 RPM. I thought the measurement was vacuum plus mechanical (without knowing a clear cut number to achieve)? Is it coincidence that both times I’ve looked at this car recently the total all-in is equal (+/- 1) to vac plus mech? Where am I missing something? And thanks again!

 

[melsg5]

Ideally 36 at about 3,000 rpm is initial timing plus the advance created by the weights moving. An additional amount of timing from vacuum is 10 to 12 degrees for a total at cruising speeds above 3k of 46 to 48 degrees.

 

[cammerjeff]

Anouther thing to check besides upping the idle speed a bit is belt slippage, at low RPM I have had glazed belts slip enough to cause the GEN light to flicker

 

[Kraig1957]

I had a poor ground from the engine block to firewall cause the same problem at low RPM. Besides fixing the ground problem, I didn't like just having a GEN light so I added a Volt meter.

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[Classics Fan]

Dialed initial advance down to 10, both mech and vac measure 19. All-in is 35 (?) at 2550 RPM. The car runs almost literally like new. Hot start after 10 or 15 minutes of cool down from operating temp is still a little slow but I will live with the 3 or 4 seconds of crank in those conditions as long as I’m confident it will fire. I’m thinking it might be fuel related at this point. I’m going to hold off from doing a distributor recurve until I see how the car runs over time.

This has been a fun learning experience for me. Never too old to learn new things, right? I appreciate the shared knowledge, thanks!

 

[melsg5]

Not sure if this is your first carbureted car, on hot start you have to hold the pedal down about 1/4 of the way and then crank.

 

[Classics Fan]

Not sure if this is your first carbureted car, on hot start you have to hold the pedal down about 1/4 of the way and then crank.

LOL! No, not close. I’ve been driving since 1973. Currently I also have a 1974 Ford Ranchero and a 1971 GMC Jimmy. They are all in pretty superb condition mechanically, and I do all my own wrenching. Kind of a jack of all trades, master of nine but not afraid to tackle anything I feel is within my ability. The Jimmy is my around town daily driver and I’ve got it tuned to where it starts in any condition within 1 second. That was done by ear and a simple non-advance timing light. Not even a vacuum gauge. Same with the Ranchero.

 

[Classics Fan]

And just like that I’m back. The hot hard start issue persists. I went on a 10 minute highway test run and pulled over into a parking lot. The car started immediately after I shut it off. However after a 10 or 15 minute “heat soak”, it wouldn’t fire. The battery sounds like it’s being pulled on hard, like advanced timing. After a couple of tries, I popped the hood to get air circulation and let it cool down for about 15 minutes before trying again. It finally gave a cough through the manifold at the end of a crank. It started on the next attempt. This is identical to the symptoms before plugs, wires, and timing. When I got home, basically reverse course, it fired right up. It otherwise runs great! Maybe a flat spot in second gear immediately after the up shift from first, but I can live with that for now. Any ideas on the hard start issue?

BTW, in regards to timing, there is a short steep section of road nearby (maybe 100 yards of 8-10%) that I can pull in second gear at full throttle without any sign of detonation.