Most confusing lawnmower problem

[wits-end]

This is more of a question to pick the experts brains here, because I'm stumped, so I'll give a small history.

I have a Craftsman 6.75 hp lawnmower, model 944.368300, and although it's 12 yrs old, it has run flawlessly til last fall, when it started to run as though it was a governor problem, speeding up and slowing down, but it wasn't a governor problem.

I replaced the plug, the gas, float bowl and cleaned the carb but still it made no difference. Then I bought a new carb and installed it. Problem is, I also noticed the gas line was cracked while replacing the carb, so I replaced it too. So, since I replaced two things, I'm not sure if the problem was the gas line or the carb.

My question: Is it possible for a gas line to be cracked, but not leak gas, yet allow air to leak in when the mower is running? I know this may sound silly, but when you think about it a bit, it seems to fit the symptoms and could mimic a governor problem. My mower now runs like new. I'm just curious which was the more likely culprit, the gas line hose or the carb.

I'll be happy to read any feedback or thoughts anyone may have.