strokersix: just out of curiosity what would cause that, and what is required to fix it? keep in mind this head was completely re-worked by a machine shop about 20,000 miles ago.
Somehow strokersix's remark reminded me of an old tired 250 where I had this happen, it would just lose cylinders at idle.
The engine ran pretty good (in fact, it is the same 250 I used for the carb/intake shootout) but was very touchy at idle. I later pulled it and pulled the head, looked pretty decent so doubt that was the problem. What I did to get it to idle:
Find the dropping cylinders. Back off those 2 valves until they just clatter - at that point if its like mine, it will pick up that cylinder again. The lifters were acting like solids - they would only idle at zero lash or while clattering. IIRC I swapped a couple lifters for new ones and that fixed it.
A little messy but it solved the problem. Probably wanted a new cam&lifters but the engine got swapped for a 292 so it is now on the wait list.
Also, try swapping 2 plug wires. If the dropping cylinder moves with it, you know you have a bad wire.
Also, don't rule out the intake gasket. Especially if it runs good at speed - could be a leaky gasket. I've even had em where they would idle good cold, but then when they warmed up, the exhaust would get hot and push the intake away from the block, causing leaks and rough idle. This came from me being cheap and trying to re-use intake gaskets too many times, but at least I knew what was going on.
