On the newer 289 carb's the pilot jet bore is generally too small and/or can have swarf in the hole........The jet block needs to be carefully removed and the tiny pilot hole at the front drilled out with not more than a 0.020" drill........any larger and the engine will run too rich. Sometimes the new pilot adjusting screw is not fully seated in the carb body and this gives a false reading. The fit of the carb spiggot on the manifold is important too, as a loose fit here will draw in fresh air that will also cause a lean mixture........The standard number 4 slides can make the carb spit and cough back until the engine is up to opperating temperature......Often I simply trim off 20 odd thou off the base of the slide and clean up the sharp edges with a dremel or similar.........this will simply allow the slide to sit slightly lower in the carb body thus lowering the cut away area and helping give a slightly richer mixture for better running and easier starting. The removal of the material off the slide is done in a lathe.......an internal mandrel is not necessary if the slide is gripped carefully in the chuck.........excess force is not needed, it is only brass, and it machines easily.........you can effectively modify these slides several times without destroying them........new ones are expensive and not needed.........For interest sake, a number 3 slide will be way too rich, and a number 3 1/2 can also be on the rich side as well.......So a 4 with 20 to 30 thou max removed off the base is plenty. The new 276 carbs do not seem to suffer these issues.......the body of the smaller carbs is actually a lot smaller than their bigger brothers........the air flow characteristics obviously plays a big part in it.........Cheers.
