Timing "could" be it all, but I doubt it's all of it. For sure a major suspect in a contributing factor.
- Is your throttle going all the way open when you floor it?? That has got many people, smart people too.
- Timing, get it right. READ THE PLUGS !!!! Plugs will tell you the initial AND total, and if it's right.
- Compression test. Some have "thought" the engine was up to snuff, only to find a cylinder or two around 80 psi (not good!)
- Take your time, and pay attention to detail. Don't let 7 of your friends each have a half hour alone under your hood to solve it :D :D