68 ignition trouble
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68 ignition trouble - 6/22/2007 7:52:43 PM
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ax
Posts: 52
Joined: 6/22/2007
Status: offline
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Hi All,
I have a 68 327 with a strange ignition issue. I have replaced all the main parts..Ie.. points, cap, rotor, plugs and wires, coil, and still have stalling at low RPM. I have tried 2 rebuilt carbs...1 Q-Jet 1 Holley with the same result. Some of the cyl's seem to be misfiring. If I remove the plug wire from the cap and let the spark arc from the cap to the plug wire the cyl. will fire. When the wire is pushed all the way into the cap it will stop firing. I tightened the gap from .35 to about .30...same problem. The plugs I'm using are ac delco r45s. and standard silicone 7.5mm wires. My thought is that the old points type ignition is just not putting out enough juice to fire the modern plugs and wires reliably at low RPM. The fact that I can get them to fire leads me to think it's not a valve/head problem.
I was thinking of trying the pertronix ignition conversion to up the volts to the plugs.
Has anyone had this problem, and if so, what was the solution?
Any help or suggestions would be GREATLY appriciated.
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RE: 68 ignition trouble - 6/23/2007 3:08:35 AM
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78buckshot
Posts: 654
Joined: 1/28/2007
From: Michigan
Status: offline
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Hi ax, welcome to the forum. Your point style ignition should have no trouble firing the new age plugs IF the distributor is in decent shape. Did you use high quality parts? Plug wires are not actualy wire but a carbon core to reduce radio interference, make sure to use a wire designed for the lower voltage system. Pull the cap and rotor back off and check the distributor shaft for worn bushings, you should not be able to wiggle the shaft sideways, any movement in this area will change the dwell as the engine changes speed. If the shaft and advance weights check out OK then double check the dwell, also I would not use the UNI-POINT kit, I don't know if that is still available but they were not as high quality as the seperate Delco points and condenser. Again I stress use good parts and the proper dwell and timing and it should not have an ignition missfire at low RPM, let us know what you find.
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RE: 68 ignition trouble - 6/23/2007 5:54:08 AM
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ax
Posts: 52
Joined: 6/22/2007
Status: offline
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Thanks Buckshot,
The points I was originally given at the parts store were the uni-point type, and I also have tried the 2 peice set. I was going to try a different set of wires, and will get a low voltage set,(actually didn't know they had specific low volt wires) as that is my last resort before giving the pertronix conversion a try. The distributor seems in good shape. I removed and cleaned all the parts, and everything seems to be working properly. I might just get a dist. rebuild kit as well, just to be sure. The conversion kit uses the stock dist. anyway, so it can't hurt. Thanks for the tips!!
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RE: 68 ignition trouble - 6/23/2007 12:15:41 PM
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78buckshot
Posts: 654
Joined: 1/28/2007
From: Michigan
Status: offline
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Hey ax, one other thing I thought of, check the primary voltage at the coil, that's the small wires on the threaded teminals, should have full battery voltage, you might see only 9-11 volts while cranking but with the engine running it should jump up to 12.5-14.5 roughly. Low or intemittent primary could cause weak spark.
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RE: 68 ignition trouble - 6/23/2007 12:40:16 PM
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73shark
Posts: 1097
Joined: 4/18/2006
Status: offline
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quote:
ORIGINAL: 78buckshot
Hey ax, one other thing I thought of, check the primary voltage at the coil, that's the small wires on the threaded teminals, should have full battery voltage, you might see only 9-11 volts while cranking but with the engine running it should jump up to 12.5-14.5 roughly. Low or intemittent primary could cause weak spark.
I think you have this backwards. You get full battery voltage during cranking, then it drops due to the ballast resistor or resistor wire to prolong the life of the points by limiting the current during normal running. Also full voltage during cranking helps make up for the voltage drop caused by the starter motor and/or poor condition of electrical system in general.
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So many toys, so little time
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RE: 68 ignition trouble - 6/23/2007 1:21:50 PM
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ax
Posts: 52
Joined: 6/22/2007
Status: offline
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Got 12 volts with Ign. on, points open.....6v when points are closed. 12 v when cranking or running.
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RE: 68 ignition trouble - 6/23/2007 2:10:58 PM
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73shark
Posts: 1097
Joined: 4/18/2006
Status: offline
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Sounds like the ballast resistor/resistor wire has been removed. Running 12 volts all the time will make short life of your points. 
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So many toys, so little time
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