I have just taken off my intake plenum and have found my lower intake looks exactly like yours AA. only the one on the far drivers side is a little wet looking. i'm assuming that the intake valve is not sealing right and leaking fuel into lower intake. anyway a little off track. thanks for the info on the cleaning i'm going to try that. thanks SC and AA

 

I've done the same thing curti420 did with the GM top engine cleaner. It works great in dislodging buildup on the valves and combustion chamber. Its a lot easier to do on a carburated car, just slowly pour it in without killing the engine. At the end of the pouring the can in, you pour just fast enough to kill the engine. The water method is also good. I've done that too. I had a '85 Monte Carlo with a 305 that would desiel on after the ignition was turned off. This is from excess carbon in the cylinders, carbon stays hot enough to ignite the fuel without a spark. After the GM top engine cleaner and a can of water, it would shut right down. I finally sold that car after the odometer hit 175,000 miles(yes, the original engine). And that engine never even had a valve cover removed, and had the original timing chain.

The instructions for the GM top engine cleaner are on the can and just as curti420 said. It works, give it a try, a can is not that expensive.

But, I think your problem is not just the carbon in the intake or combustion chamber. Does the idle seem higher after you removed and replaced the intake? My guess is that there is a vacuum leak somewhere in addition to any ignition problem. See if the new distributer cap and rotor helps, if not, check for vacuum leaks, or put a vacuum gauge on and see if its low. I think the intake manifold gasket may be suspect. I can't imagine it would be ok to reuse an old intake gasket. You could spray some WD-40 around the intake manifold where it bolts up and see if the RPMs jump up. If they do, you have a vacuum leak. Just don't start a fire.