Only 5 inches of full manifold idle vacuum when warmed up is a sure as hell sign of a stretched timing chain and or retarded timing . here is a typical GM high compression 4 bbl advance curve from a wedge chamber type head like yours from the 1960s. With today’s fuel you might want to run the same 10 degrees of initial, but limit the total mechanical advance to 28 just off idle depending on your cars rear gearing and the pump fuel you can buy in your area. This is just a suggestion of what to start with. note that at 100 mph and full throttle there is 1” of vacuum being pulled, this is a sure sign that the Carb could be a tad bigger.
I think it is more likely that he was measuring a ported nipple, and the throttle was open far too much because of the retarded ignition timing. Hopefully, the OP updates us soon.
I turned the distributor counter clockwise and the mark on the damper moved towards 6 o'clock before killing. Restarted car and turned distributor clockwise until the vacuum advance hit the firewall. Damper mark moved towards 9 o'clock. Pulled distributor added pertronix points conversion and retimed correctly. Car runs much better, still have some hesitation but much better and no popping noises in the intake. I will need to pull the distributor again to put the advance limit bushing in. I am in the process of locating one. The original was no where to be found. Advanced initial timing a bit and pull 21 inches vacuum steady.
on the driver fenderwell is a battery relay. there 2 wires that go to it. pull off the connection and see if it is corroded. my 65 would idle, but would get funky above that. happened to touch it with my arm and everything went fine. damn corrison
Before I did anything else, I would establish that #1 cylinder is at TDC. Use a pencil, a long Q-tip or whatever you can find that will touch the top of the piston. When you wrench the crank pulley bolt until the #1 piston is exactly at TDC then look at the timing marks; The line on the crankshaft harmonic balancer should align with 0 degrees on the timing index, if it doesn't, the harmonic balancer outer ring has slipped on the inner core. You need a new or different harmonic balancer. If the marks do align, the timing marks are correct and I would look for another problem.
Going back to the OP, if you pulled the vacuum advance hose "with no apparent change", (assuming that there is vacuum at the hose) I would be suspicious of the vacuum advance itself. Check to see if it holds vacuum. I do it the easy way - I just put a hose on the advance unit and suck gently on it (I know that I'm opening myself up for some comments, but every car person that I know checks advance diaphragms this way). If it's bad, replace the unit. I doubt that this is your entire problem, but it will never run really well with a bad vacuum advance. I agree with trunk monkey on the harmonic balancer. You will have to find a good used one or contact Russ Martin at Centerville Auto Repair. He advertises new (not rebuilt) units, but I don't know whether he has any in stock, and they are pricey. He's in California, give him a call. (530) 272-1564. I know this post was early May, but if you have had difficulty finding parts...
Thank you for the continued responses. 66 california carb only has ported vacuum nipple. I have confirmed that vacuum advance works by using suction and also changing to manifold vacuum. I pulled the distributor and reset timing correctly, the balancer is correct for tdc on #1. I picked up a recurve kit with the limit bushing and installed that and lighter springs. 1 light 1 medium. Car runs very well now and is responsive. Thanks, Josh
Keep a eye on that light silver springs that come in those advanced curve kits!!! They go south Kind of fast and then you will find that at high rev's your timing is bouncing around due to lack of weight control. I lost the rod bearings in a race motor long ago due to this condition so I know what I speak of, but anyway I would bet that if you put in two of the same medium springs you would really not feel a difference in responce.
