Well, I fixed the rich problem, but still curious as to what's up. Here's the story...
I've got a '68 w/ a 327... headers, moderate perf cam (but plenty of vacuum).
Always smelled a little gas, and ran rich... some rare plug fouling problems... occasional backfire through the exhaust. Had a qjet, R43 plugs, points, 8 degrees init (ported) advance.
This winter, car was apart for some unrelated restorations and I decided to replace a few engine parts too. Went to a Road Demon, Performer intake, and Accel Billetproof distributor.
Guess what? Same problem... only worse. So, installed R45s, upped the timing to 15, took the jets down by 2, lowered the floats (to the bottom line). Things got better, no longer smelled gas, but, still eventually fouled plugs! Note: secondaries are closed at idle.
So, I bought a set of Demon's idle feed restrictor (IFR) inserts, drilled them to 0.029" (stock IFR is 0.031"). Finally the problems are gone. Car runs great.
My question to you all - what would make an engine want a more leaned out condition like this? Even now, the best vacuum (about 17") is found with the idle screws 3/4 out. Demon recommends no less than one turn, so I have them at 7/8. Tempted to take the IFRs even smaller.