have ya checked for vaccuum leaks? Mine runs like crap when some of the vaccuum line plugs get old and start to crack. I keep a handle full in my ashtray just for that reason. Maybe a good old fashioned tune up would be a good start. I just put a newer motor in my 85 nissan, went from a 2.4 napz to a 2.0 without changing the jets or adjusting anything and no problems. Also, check the set screws, mine tend to back out real easy, causing mine to run rich at times! And I have to adjust mine for the seasons too! In the spring and fall I have to adjust the choke and the idle! Hope this helps out!