Get new plugs. Sometimes they can look clean and good but are actually no good. Particularly because they will have burnt the oil away the first couple of times they fired. A good spark out of the engine isn't always a good spark with compression.

There is a $3.50 NGK plug that works that I have always used. You can commit to $25 a pop iridiums but you may not need them so you may as well just the cheapies to rule another thing out.

Do a search around the place. I know I've listed their part number somewhere before.