I just did a head swap with a bunch of other stuff, starter, clutch, tranny, and all upper gaskets. Back together now and I have a hesitation at about 40 miles per hour or so, like low midrange rpms at roll-on. Gas mileage has dropped more than 5 mpg, and there is noticeably less power. I changed the head due to bad valve guides, the engine ran great before but used oil. At least that got fixed.

Took it to a guy who diagnosed it as funk in the distributor cap, and I've seen much worse so I said no thanks, especially since it ran like a raped ape before with the same distributor. I un-advanced the timing a little and that seemed to help, but not much, should I try more? I cannot find anything like a vacuum leak, but it seems like it runs a little lean, but I could be wrong. The new head came with a cam, but it didn't look any different from the old one. I've adjusted the valves twice now, they are doing fine, but there is considerably more engine noise than before (like tapping but not pinging.)

Have any ideas?
Thanks
WiredForStereo