After being garaged over the winter I brought out my 78 Bronco with a 351M engine to take it around the block. The engine was missing badly.
All eight spark plugs where full of carbon. I got a tip that the enrinchment valve on the bottom of the motorcraft 2150 carb might be the problem so I pulled the carb, uncrewed the cover to the envrichment valve and made sure it was clean and that there was no tears in the diaphram. I also sprayed carb cleaner to clean out the passages leading from the enrinchment valve.
I put a set of new plugs in, a couple of laps around the block these set of plugs where carboned up. The last thing I was going to try before rebuilding the carb was to replace the choke. I noticed that when the engine was completly warm the choke plate is not completely open. It is a 23 degrees short of being fully open.
Oh, I made sure that the EGR valve opened and closed properly when vacuum was applied to it.
Thanks!