California cars did not have a road draft tube? Do you have any diagrams of the system they used? My intake had a freeze plug in the back of the intake and this aroused my curiosity. The plug looked original. I removed it to install a modified PCV setup.
You bettcha. In California Circa 1962 the only permitted system applicable to new cars was the PVC valve. It went onto a closed tight system. Which means no road draft tube. The PCV was connected in on all autos (trucks like the Jeep note in the above link) were exempted. This also was not a retro fit installlation either. It did not initially apply to 1959, 1960, and 1961 autos, but after discussion in Sacramento that got changed. It only applied to brand new autos sold within the state, unless they were of flathead design (like your B&S lawnmower engine), or had multi carburetors, or F.I. like the Corvette. Later in 1962 they modified the regulations to apply to older (pre-1962) vehicles still on the road, but not trucks.
The principle was simple. The California Air Board thought SMOG was caused by BLOWBY of oil or what ever got past the piston rings. Thus they figured out a reburn system, similar to the air pumps of a few years later on. The crankcase was put under negative pressure, awaiting the blowby, and the negative pressure then made the bad elements go through the one way valve, and then get sucked into the carburetor, and burned once again. The valve is one way. This because of possible backfires. They did not want the crankcase to explode. So the one way check valve was used. They also did not want fresh air entering the crankcase via a third way (an unplugged road draft tube), and lousing up the operation of the PVC system.
There were no holes permitted in the valve covers, no road draft tubes permitted, or any other thing to let outside air into the closed system. They also had a special non-vented oil filelr cap for the cars. They used to test the the 1962 engines via a gauge on the valve cover and it had to pull about one PSI in order to pass. If it was higher, like your engine had blowby, then it had to be torn down and fixed.
For 1963 all rules got altered, again, the PCV had to be used but in conjunction with a few other items too. Nothing was altered in 1964, but when 1965 came along then.....
I think that later on, the auto manufacturers (with new rule changes) said da Hell with putting in a hole in manifold back for a road draft tube, if the laws are going to say no. To go along with the change in legislature, when you bought a conversion kit for a 1961 or earlier auto, they gave you a tapered rubber plug to shove up the road draft tube.
I still got all my required (Retro) equipment on the 1961 Thunderbird, and am 100% legal to drive it.
That plugged off manifold was for a reason, not a freak.