Toyota Repair: 88 Tercel Carb, intake manifold gasket, vacuum hoses

Question
I have an 88 Toyota Tercel hatchback, made in Dec. 87,217000 km, 4 speed manual tran, 1.5,3E.  It began to idle very rough, diesel, and have trouble starting (it took many turns over to start). I brought it in to get looked at and I was told the carb should be replaced.  I replaced it myself, and the problems remained and I was told the carb was faulty and that Toys of this type had problems with gettin a carb that works. I just replaced it myself again, but the rough idle remains and it still diesels.  I checked the PCV valve and it was fine, replaced any vacuum hoses that looked evenly remotely worn.  I made sure the carb was securely fastened to the manifold to prevent a vacuum leak, with a gasket, as well as had the timing adjusted, and I had the idle adjusted.   What tightness should the nuts on the manifold be tightened to (ft-lbs)?  Can you suggest anything else that could remedy this problem?  I am a working college student and any help I could use myself would be greatly appreciated.

Answer
There may be an intake leak at the intake manifold gasket betwwen the manifold and the cylinder head. With the engine running spray some carburetor cleaner or brake cleaner around the bottom of the carburetor and also along the intake manifold gasket area, if the engine speeds up that is where the leak is, since two carburetors have already been put on I doubt if the carb is the problem.
If there are no intake leaks I suggest you have the engine compression checked to make sure there is no internal leakage, also have the headgasket checked, there may be a blown headgasket.