My buddy's the original owner on his essentially mint '74 MGB with 103k miles on it. He didn't drive it much the last few years and it sat in his garage, but he maintained it. He thought he needed new carbs, so he had it flatbedded to Frank Monise in Pasadena, CA, to change fluids, put new carbs on and get it ready to drive around again. He went by when Frank said the car was ready. Mitch picks it up and gets about 1/2 mile away and he gets his recurring problem that he thought the carbs would heal. When the MGB gets warm he looses power and eventually will only idle. Now Frank just told him that a valve job will cure it (why didn't he mention that in the beginning as Mitch told him the problem). Mitch spent 900 on the carbs and a total of 2400 with all the little things he had the guy do.

His problem doesn't sound like valves to me, as Frank didn't even do a compression check, and I'd do one cold and warm to see if there is a difference. Mitch describes the problem as similar to vapor lock. Something's screwy, but it ain't the valves in my opinion. No smoking of any sort, no missing, and it runs normally to a certain point when warm. No rough idle either. Any ideas? I was wondering if maybe the intake manifold might be warped and leaks when warm. Maybe the gas tank or venting, although Frank supposedly cleaned and sealed the tank.