I've got an '83 that seems to run great when cold, but once it warms up it seems to drop a cyl.until you hit about 2500, then runs good, it seems to idle fine too. I've replaced the plugs and diaphragms. years ago I had a similar problem [i think] and it had a bad diaphragm. stumped now,think it might be valve adj? or electrical? If I just rev it up it sounds good, but on the road it doesn't matter how much I wash it, it looks like dung under 2500