I ran a 250 with epoxy in the ports for a couple of years with no problems (with the epoxy). I made the mistake of going with bigger exhaust valves and keeping the stock intake valves. Using our flow bench I was able to gain quite a bit of exhaust flow and some intake (about 10%). The intake was mostly low lift flow which should provide good of idle and midrange torque. It ran really good under full throttle and off idle, the problem came in at mid range, like pulling a long hill where the throttle is open quite a bit. The exhaust pulses would pull so hard, the intake charge was being pulled right on through, causing extreme lean out. Simply letting off some or going full throttle would bring it out of the lean condition. I tried for two years to cure the problem, I finally replaced the head with a stock rebuild and the problem went away.
Some day I will install bigger valves in the intake and try again. The lumps direct the air up and over the flat floors so it enters the valve opening at a better angle. My epoxy does the same thing. I left the bolt boss in place, so that wasn't helping either. You loose so much port volume with the lumps, it takes removing the boss to gain back what you loose. That was probably hurting my head as well, but I just couldn't get myself talked into cutting them out. Dad and I have seen heads ruined by opening them up to much, and I just didn't what that to happen.
Joe
