Thanks all for expertise.
Timing: running a Pertronix 6 volt module with a new advance diaphragm. Haven't measured exact advance at RPM with my old advance timing light but before pulling the head yesterday it started at 5deg. BTDC and moved smoothly forward at throttle. I don't think timing was a problem.
Carbon fouling: the valves I pulled out were showing obviously over-rich. So if anything the engine should have run cooler, as I am aware fuel evaporation cools, too lean heats!
So the overheating (new radiator, thermo and all hoses) may have been an old brittle head whose time had come? When I had Wayne's Engine bore the block they failed to resurface the deck, and there was a gray area in communication there when I picked it up. I assumed they had checked it and decided it was OK. May be warped. But I ran this Offy setup for a couple thousand miles before the overheating began.
Offy's Instructions: to quote directly "Use two same make and style carburestors. Standard jets and metering rods are most universally used. Float level as per specification for type carburetor normally used. Set accelerator pump on shortest stroke that driving conditions will permit. Ideal Mixture--set both carburetors exactly the same."
Now how's THAT for an instruction manual?! Not a word about reducing or enlarging any jets, just shortening the mechanical power pump stroke.
Vacuum power piston/metering rod and related check valve/power jet: if I understand CarbKing correctly, maybe this small jet under the check ball in the Main Well Support will need be reduced, as the port will open sooner, due to dual carb reduced vacuum signal off throttle?
If there is a way to increase the reduced signal to the brass (?) power piston to hold it up, and thereby the check ball closed longer, as it does normally with the single carb vacuum signal I am totally in the dark as to how to accomplish that.
CarbKing's suggestion of going with mechanical power circuit carbs sounds a helluva lot easier.
So, after I've rebuilt the entire damned engine again (it's the journey, not the destination, right?) what carbs are a good replacement for an Offy designed to mount Rochester B's? I'd have to obtain some kind of adaptor...
Any suggestions on carb replacements and observations on brittle fifty-year-old cast iron are welcomed. Thanks again.
