I have a similar problem. Bought a new 661 in May, probly put a dozen or so tanks through it, with no problems at all. Then about 6 weeks ago I noodled a few bits then stopped the saw. Attempted to restart it while warm a few mins later and it turned over, coughed then flooded. Took the spark plug out and let it dry, cleared the cylinder, put all back together again. Tried to start, same result. Did this several times. Tried swearing at it, that didn't work either. Let it sit for half an hour and tried again, it started, turned over a few times, coughed and flooded again. Let it sit for another half hour then managed to get it to run. Once running, it was ok. I haven't used it since but got a mate to have a look at it (he's a small motor mechanic, I know next to nothing). He said the spark is inconsistent, maybe sparking properly one time in three otherwise with a weak spark or no spark. The various bits individually test ok but all put together don't work properly. He says he has seen it once before in a stihl, and replacement of the EDI unit resolved the problem. It's still under warranty so I'll take it back and they can sort it out.
