As to putting a 4bbl on a stock slanty;
in a quest for a smooth idle, is um ,IMO, borderline insane.I have to agree with Dan.And to put one on for any other reason is still insane.
But if you have heavily modded your slanty,well that's another matter.
So as Dan said,if the engine idles rough,and the carb is known to be good, with a correct T-port sync,and fresh enough gas, and the ignition is also known to be good, then it's time to check the mechanicals. Starting with a compression test and a vacuum test.Then setting the valves and a new compression test.And finally if nothing has yet turned up, a leakdown test. One of these will point to the problem;Unless a mistake was made upstream;as in the carb and ignition.
Of course the condition of the PCV is a wildcard. If that baby is flowing too much air at idle, well you just caint tune that out. Or if one of the vacuum devices has a ruptured diaphragm, it might give you a little trouble.Or if your engine is one of those that just plane wants the airfilter house installed to run right, and yours is on the workbench, well you caint tune that out either.Or if the springs in your dizzy..... Well you get the idea;the devil is in the details.
