I have not flown the O-240 version, but have quite a few hours in C150s and C152s. For me the O-235 was the better of the two engines, mostly because it was easier to start in cold weather. With the priming setup of the O-200 engine it was quite easy to get a carb fire if you didn't follow the steps to the letter. And as we used them to train ab-initio pilots at a medium sized FTO... I have encountered a few of them.