I've built a few over the years after having done my research . All bar two produced what was expected of them.
One was nowhere near the power levels it should have been. After a lot of checking and double checking ( also had a mate who knew his way around the engine check that I wasn't making an obvious mistake over and over) . It turned out a brand new cam had the wrong number stamped on it and was totally unsuitable for my engine.
The other one was a bit wilder but never ran in my possesion. Two owners later I got involved with getting it running. It ran like ****e again. This time because the owner hadn't run the fuel lines to the multiple carbs correctly. He wouln't even let me put it back to I had planned to be set up I belive because he didm't want to lose face.
A mate asked me to set up his engine using same carb set up. I agreed on one condition that I did it my way . He agreed, it started first , and idled and reved exactly as it should.
Earlier someone else had asked me to set up a similar carb set up on their all singing all dancing painted and plated to death engine.
It wouldn't run worth a damn. Upon further questioing it still had original plugs, points , leads etc and he hadn't even checked preload on his new cam and lifters.