There are 2 things that made me realize that the timing had jumped suddenly. The first was that the timing was all of a sudden waaay retarded and therefore running very roughly. This is what caused me to tear into it initially after all the other ignition components checked out okay. The second thing, and this is what verified it for me, was that when I lined the new chain up, it would not match up with the marks on the sprockets-- it was exactly one tooth off. So, I had to slightly rotate the crank to get everything to line up-- and then made sure that the driver's side part of the chain was in tension, and the passenger side had slack. Anyhow, I'm pretty sure it's not that, because when I fired it up the first time after replacing the chain, it was only about 1 or 2 degrees off on the timing light (I had marked the distributor and put it back in in the same spot).

I've never adjusted the TPS-- I'll look into that to see how it affects things. Thanks for the advice. <img src="/forums/images/graemlins/kewl.gif" alt="" />