A couple of things I use when diagnosing engine related issues. If you think there may be a vacuum leak take an unlit propane torch, acetylene would also work. With gas on for the torch hold it close to areas where you suspect a vacuum leak. Pay particular attention around the carb, carb base gasket, around the intake where it bolts to the heads and any vacuum lines. If the idle increases or smooths out you found a problem; fix that problem and continue testing to make sure there isn't more than one cause.
As a check on the timing you can use a vacuum gauge in conjunction with your timing light. If the vacuum is out of wack, i.e., low, it may be that your timing chain needs to be replaced. Before you rush to replace the timing chain and gears you should check for vacuum leaks and that the issue isn't carb related. If all else checks out then I would physically check the timing chain and consider replacement.
To help diagnosis and setup the carb use a tach and vacuum gauge, you may have an air screw that needs tweaking. If your car is stock, especially the cam, you should be able to adjust the air screws and get 20" of vacuum.
A vacuum gauge is a very useful tool, can also indicate if you have a sticky value etc. I use one with every tuneup.
As SD 396 stated, you never had anything major apart.
It ran 100% fine before the body job. So don't focus on anything internal.
You changed the wires and plugs I assume, added a pertronix and rebuilt the carb.
It's ignition related I bet. It's not intermittent, you report it as a timed miss. Can't see the carb or a external vacuum line leak causing this.
Start with a new quality set of plugs and a Cap. After that, if no change, find another long ignition wire and start pulling wires one at a time and putting the temporary one in.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
As mentioned full 12V is important for the Pertronix to work properly. Any slop in the distributor shaft? Is your float level set correctly in the carb?
I called Barry at Performance Unlimited in London where I bought the Pertronix system.
I know he wasn't there the day I bought the system.
He always recommends a cap with copper connections.
Of course I have an cheap aluminum style cap.
He said that oxidization can cause problems.
Picked up an MSD cap off him.
He also insisted that I call him, when I have the cap on, to let him know what happens.
Love these small shops !
I'll pick up some Seafoam, couldn't hurt !
i bought the Pertronic distributor for the 66 but only have the stock coil. I looked at the flame thrower coil and there is a number of them with different ohm rating what one do I need? help would be great thanx
Buy the Pertronics coil to match the ignition you bought, their site says which matches.
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic