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Hope someone can diag my issue, here are the facts. 72 350 4 bbl, unsure of internals Edelbrock manifold, 73 rebuilt Q-jet, headers. Set timing to 12-14 btdc, set carb to vacuum gauge (18# steady) new wires. HEI dist, manifold vacuum. Set fast idle and choke.
Runs rough and will not shut off with key.
Anything stand out? You won't hurt my feelings. Thanks.
Recorded a video to go with this,
You are getting power to the HEI Batt terminal with the key in the off position. Where is it hooked up? There are also posts regarding some alternators that back feed power through the system with the key in the off position in which there is a diode mod you can use to block it.
I read about the alternator and the diode, but it did not refer to the one wire alternator. Quite possible on the other, I'll check tomorrow. Should have mentioned that I used a Painless wiring kit designed for the key in the column, but wired into a dash mounted generic key switch. So, yeah, that's possible. However, if power were still to the dist, B+, why then when key shut off does it act like dieseling, not continue running with no change?
It acted like it suffered a voltage drop and then managed to continue to run with it. Measure the voltage at your Batt terminal when the key is turned off, willing to bet you have some.
My first guess would've been the alternator - it's happened to me. But a one wire alt setup doesn't have that problem.
In a normal 3 wire setup, the Field/Energize line is powered by the ignition circuit to energize and kick-start the alternator. Once it's running, the alternator can generate its own current and back-feed on that line into the ignition circuit. It's not a lot of current, but can be enough to run the ignition.
Since you don't run the plug harness on the alternator, there must be something else that's feeding current into the ignition circuit when the key is "off". Unfortunately we've exhausted the common cause, so you'll have to trace your install to see if there's a bridge somewhere. Maybe used some of the pins on the key switch incorrectly? I recently re-wired a 65 C10 and had to be a bit creative because the dash key switch didn't have all the terminals the wiring kit wanted. It can be tough to tell what the terminals are as well.
Thanks. I ran it with the alternator disconnected and the problem persists. Also checked that no current was running to the dist. after shut-off. Still runs on. Checked the ign switch wiring, all looks good. Hmmm.
Also checked that no current was running to the dist. after shut-off.
Obviously that is not true.
Temporarily run a piece of wire out of the BATT connector to the HEI. Use a voltmeter to check for voltage there. When the engine continues to run with the key off, what does the voltmeter show?
Doubt the tach would have anything to do with it as its on the ground side of the coil. Most often with a tach problem, the engine won't run at all. As Joe stated, obviously you have voltage to the Batt terminal or it would turn off.
Try colder plugs. It is dieseling. Usually from a hot spot in the chamber. Plug, carbon, valve. May be sucking some fuel from the carb also. Try plugs first. Easiest.
Try colder plugs. It is dieseling. Usually from a hot spot in the chamber. Plug, carbon, valve. May be sucking some fuel from the carb also. Try plugs first. Easiest.
What would you recommend as a colder plug? Go into a parts store, I'll get the stare!
To answer Joe's question, no voltage when run-on occurs.
More when engine hot than when cold.
Have taken the wires off the key switch and cross wires to start. No difference.
Heavy fumey gas smell.
Still would know # for a colder plug.
Thanks again.
Take one out and take it to a parts store. Ask the counter person what they have. I think some plug mfg may have as many as 10 or more different heat ranges.
Thanks. Some other things that concern me is the carb. With a SBC, one would only run a 600-650cfm, but on the 350 Olds, a 800-850 is recommended. The carb I have is stock for a 73 350. Could it be too much carb?
Also, I'm wondering about carbon build up. As I said, I've not had this engine apart. I remember years ago, I had a 79 Cadillac that had very low miles for the year and it started to knock so bad I thought the engine had gone. Took it to a mechanic friend who at 2000-2500 rpm, trickled ATF into the carb. After a few minutes, there was a tall pile of carbon under the tailpipe and the knocking was gone. Also have heard you can do this with Seafoam.
Last edited by Roger60; November 24th, 2019 at 09:45 AM.
The carb I have is stock for a 73 350. Could it be too much carb?
Your picture shows a Quadrajet carb. As long as no one has changed the setting of the secondary air valve, this carb would work on a 230 cu in six cylinder as Pontiac did in the 1960s No, you do not have too much carb.
Runs rough and will not shut off with key.
Anything stand out? You won't hurt my feelings. Thanks.
That looks and sounds like bad gas to me. My 67 would do that back in the 1980s when i put too low of an octane rating. It was a low compression 330 and it hated 87 and 89 octane. 91 octane worked but i eventually kept her satiated with a steady diet of Sunoco Ultra 94. (Boy do i miss that gas !)
Originally Posted by Roger60
Heavy fumey gas smell.
Same symptom i had, the car would eventually turn off but it rattled, chugged, wheezed, and sputtered till the end. Painful to sit through as if the engine was dying on its last breath while fighting all the way...
Two items must be present for an internal combustion engine to run: (1) A combustible material & (2) an ignition source.
If one of these items is not present the engine will not run. If both items are present the engine will run.
You obviously have a source of combustible material - whether that combustible material resides as residue (carbon buildup on the spark plugs), residual fuel in the chamber or a continual supply of fuel - you have a fuel supply.
But, that fuel supply will not ignite without a source of ignition. That is a simple fact.
Two contributors of an ignition source are: (1) Electrical current; and, (2) heat. The most likely would be an electrical source, yet heat could be suspect. I believe the temperature must exceed ~495*F to ignite petroleum fuel. I believe the temperature at the spark plug is ~1,000*F. I suppose it's possible to maintain a temperature >495*F for a period of time after the ignition source (system) is turned to the off position, but heat rapidly dissipates when the engine is turned off. Air is not a good (terrible) source of conductivity. Air is an insulator not a conductor. It is possible the fuel itself is >495*F but I highly suspect this is not the case.
Why does the engine continue to receive spark? Some item w/in the ignition system is continuing to supply spark to the combustion chamber. It most likely resides in the positive (source) pathway not the negative ground pathway.
I would examine the most likely positive source pathway(s) of the ignition system. Some electrical item is either hooked up incorrectly, or something has or is failing along this pathway - that item is continuing to supply a source of ignition.
In the video you shared, you pulled a manifold vacuum source to stop the engine. I assume that vacuum source is to the distributor vacuum advance yet, even then the engine slowly stopped, it did not stop immediately. The engine should stop immediately with absolutely no after burning. With the engine running, remove an electrical source: (1) remove the positive terminal of the battery (even though a modest electrical charge will continue to reside w/in the electrical system for milliseconds after the positive cable has been removed) - the engine should stop; or (2) remove the coil wire itself or any other electrical ignition source - the engine should stop immediately.
I've installed new plugs, so no build up there. Will pick up a set of colder plugs today. I can say that through all my tests that there is no current after the key is shut off, but, to your good point, I will try disconnecting the pos cable at that point. As far as gas, yes it is low octane. I will remove it and go with 93, which is the best we can get here. Thanks.
Thanks to all who came to my aid on this problem. I am happy to say it is fixed. I bought this 350 from a fellow hot rodder on Craigslist. Knew him from local car shows, so I felt confident. Also was a very fair price and came with a transmission and other parts as well. Anyway, the plugs in it were Autolite 82"s. When I changed them the first time, I pulled the new plugs from my extra 330, which were also Autolite 82"s so I thought I had the correct plugs. Nope. In Autolite it takes a 26. The correct plugs I installed, thanks to your responses, are AC Delco 45TS. So to use a colder plug, I went with a 44ts. Also drained the tank and refilled with 93 octane. As I installed each plug, I thought to check the compression. All 195-200. Kinda explains why it didn't run well on lawnmower gas. Any way, with those small changes, the problem is solved, no run on. Also corrected the timing as the changes tossed it off a bit and tweaked the Q-jet. Waiting for a set of remflex (I knew better, got in a hurry) exhaust gaskets to arrive, and it might sound better, too. Again, my heartfelt thanks.
November 21st, 2019, 12:17 PM
