Let me get this straight,
235 engine, 261 camshaft,
dual carbs, dual exhaust,
engine ran before cam change with same set up as now
14 inches of vacuum at idle,
Is that about right?
If the intake and exhaust system was working with 235 camshaft but not with the 261 camshaft, you have to suspect something is wrong with the cam profile or grind, or that the lift and duration is just to much for the 235 engine with a marginal intake system. A bigger camshaft moves the power band up the rpm scale, it also lowers the vacuum, you should have 18-19 inches of vacuum, not 14.
Are you 100% sure the camshaft is timed to the crank correctly? Dots are lined up?
Don't worry to much about the timings actual number, turn it till it starts and runs and keep messing with it to see how it acts. If you find it's way off its mark, yet runs better, suspect the camshaft again.
As a test, block off one carburetor, doesn't matter which one, then get the truck where it will run the full rpm range without any trouble. Swap the block off plate to the other carb and get it running correctly. I have used a simple aluminum gasket cut from a Coke can to block carbs with, then I don't have to mess with the fuel systems. Once happy with the way it runs, go back to both carbs and see how it acts.
You stated, " the truck easily accelerated up to 4000 rpm, but wouldn't idle under 1800 rpm " How did you fix this? Was this acceleration full throttle or normal driving? Sure sounds like a lean condition, not enough air flow through the carburetor to pull the required fuel out.
Joe
