I agree clutching has a huge part, but if you can tell it drops to one cylinder something else is going on. Does it act way too rich all the time? Check the HAC needle position. Sometimes the seal will go bad and throw things way out of wack. There is a screw on the back side of the unit covered with epoxy or something that has a o-ring on it, this holds an air tight seal against the diaphram or whatever inside. Mine was f'ed up and resetting it fixed it. Should'nt have to but hey they are getting old. Take the srew out and blow on it, the needle will come out the front side of the brass tube on the front. Hold your finger on the hole, it should stay there. If it doesn't you have a bad HAC. Look for a used one, new ones are way too expense for what they are. If it does hold try to reset it, low elev. moderate temp (not super *** cold or warm) should be 5-7 mm below tube (so i've read). When I did mine I was at 4500 el. at room temp and put it at flush. Use sealant on threads and o-ring. Go to dootalk.com and search for h.a.c. issuses, there is some good info there.
