I don't know which Fox engine you tried. Many of the older ones had a carb that was difficult to tune, especially if you tuned the high speed needler before. Some were made for power and others made real light and intentially had low power. Some for high nitro and som for no nitro. If you bought one without the instruction manual and did not know its druthers, you could have a problem with an otherwise good engine. And yes they had a few lemons as well.

I think if you bought a new one today and used the fuel it is made for, you would find it a very good engine.