Bob F wrote:
I have an old Craftsman 6HP vertical shaft chipper/shredder that is
giving me trouble. The engine idles great, but at any higher speed,
runs really rich, making black smoke, and even spitting gas out the
carb if I take the air cleaner off. It does not rev properly in the
process, except when it first starts or as it runs out of gas.

The diaphram in the carb looks excellent. It looks new. I might have
replaced it a couple years ago when I acquired this unit used. The
gas valve it operates seems to operate also. If I blow into the fuel
inlet, no air passes until I push up on the needle that opens the
fuel flow. I even tried installing a layer of plastic from a bag
"outside" of the diaphram (between it and the cover) to eliminate the
possibility of any leaks through the diaphram, with no effect.
Would a bad diaphram allow the idle to work great, while higher
speeds are all super rich?

The idle needle adjustment works properly. The high speed needle
adjustment seems to have no effect, other than if I remove it
completely, at which point the engine will quickly speed up like it
should work for a few seconds before it then dies.

Any ideas? Is there something I haven't thought of that could be
repaired on this carb/engine?

Thanks for all the suggestions folks. As one of the early responders said, it
turned out to be a problem with the high speed jet. An internal "cap" was
missing, which allowed gas to bypass the high speed adjustment needle. I had to
pay $11 for a carb kit that had the 3/8" aluminum dome shaped cap in it.
Replaced the cap, and it works perfectly now.